Just what is a stroker anyway? A stroker is an engine with increased or decreased stroke. By increasing an stroke (the distance the piston travels in the cylinder bore), we gain displacement. By the same token, when we decrease an engine’s stroke, we reduce the distance the piston travels in the bore. This changes when and how the engine makes power. Short-stroke engines like high RPM, where they make the most torque. Our focus here is more about increasing stroke in order to achieve greater amounts of torque and horsepower.
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Stroking an engine does more than just increase displacement. It increases torque by giving the engine more of an internal mechanical advantage. When we increase stroke, we increase the engine’s crankshaft arm or lever, which makes the most of a combustion cycle. The longer the stroke, the greater the torque or twist.
Stroke comes from the length of the crankshaft’s rod journal arm. Then, we double that length to come up with the engine’s stroke. We double the length of the crankshaft’s arm because we get that arm in two directions- top dead center (TDC), then bottom dead center (BDC). This is a simple 2:1 ratio. Take the crankshaft arm, measured from the crankshaft centerline, and double the measurement. If the arm is 1.5-inches, you have a 3-inch stroke.
Factory stock small and middleblock (Cleveland/Midland) Fords have four basic strokes. The 221, 260, and 289ci engines have a 2.87-inch stroke. The 302 and Boss 302 have a 3.00-inch stroke. The raised deck 351W engine has a 3.50-inch stroke, as do the 351C and 351M middle-blocks. The 400M has a 4.00-inch stroke.
Stroker engines generate more power in two ways. First, the greater mechanical advantage of a longer crankshaft arm generates more torque. Secondly, we are also filling the cylinder with a greater volume of air and fuel, which gives us more power all by itself. We get torque from increased stroke and cylinder swept volume. Torque is the truest measure of an engine’s power output.
When we consider the crankshaft’s arm – the distance from the crankshaft centerline to the center of the rod journal – this is where torque is born. Torque is an engine’s grunt factor. Grunt is that physical pressure at your backside when the accelerator is pressed. So what is torque exactly? Think of the crankshaft’s arm as a lever, like you were taught in high school physics class. Torque equals the downward force of the stroke times the length of the lever or arm. If we look a 5.0L engine’s 240 ft-lbs of peak torque, this means each cylinder bore is producing 480 pounds of pressure on each power stroke. We increase torque when we increase the length of the arm, which we accomplish by increasing the stroke.
We know a stock 5.0L engine’s arm is 1.5-inches. This means the 5.0L engine has a 3.00-inch stroke. If we add 1/4- inch to the arm, this increases the arm to 1.750-inches. Double the 1.750-inches and you have 3.50-inches, which combines with the standard 4.00-inch bore to make 351ci. This gives us 40 addition al foot-pounds of torque. Overbore the cylinders .030-inch and you have 355ci. Push the bore to 4.060-inches and you’re courting 360ci. You are also making more torque.
Despite the advantages of a stroker, there are disadvantages as well, especially if you’re bent on pumping the most displacement possible into a 302 or 351ci engine. When we stroke a 302 or 351 to its limits, we lose piston skirt, which hurts stability. We also push the piston pin into the piston ring land area, which weakens piston design. It also puts the pin close to the piston dome, which exerts too much heat on the pin and boss. These are disadvantages that shorten engine life.
Another factor with stroking is rod length. When we haul that piston deep into the cylinder bore, we are also bringing it closer to the crankshaft counterweights, which creates conflict. This means we need a longer connecting rod to get the piston down there without interference with the counterweights. Sometimes, we can find off-the-shelf connecting rods to complete our stroker. And other times, we are forced to custom make connecting rods that will work. More expensive stroker kits have custom parts, like rods and pistons. More affordable kits have off-the-shelf parts that have made the kit possible without expensive tooling costs.
Whenever we have to custom make connecting rods, this drives the cost of a stroker kit up. The same is true for custom pistons. Stroker kits often mandate custom pistons to keep things friendly at the top of the bore. A 347 or 355ci stroker, for example, has custom pistons with pin bosses pushed way up into the ring lands. This also drives the cost up and shortens engine life for reasons explained earlier.
UNDERSTANDING BORE, STROKE, & COMPRESSION RATIO
Whenever we increase the stroke length, we are squeezing more volume into the same combustion chamber. This means we need to concern ourselves with an increase in compression. With that increase in stroke and compression comes an increase in cylinder volume. In that volume comes an increase in air and fuel, which gives us more power.
Compression ratio is a subject that is often misunderstood. One popular misconception is that pistons, alone, determine compression ratio. But this isn’t true. Compression ratio comes from not only piston dome features, but also from stroke, bore, and combustion chamber size. Compression comes from piston travel from bottom dead center to top dead center with both valves closed. We are simply squeezing the cylinder volume (displacement) into the combustion chamber. This is called compression ratio. Compression ratio is cylinder volume at top dead center versus cylinder volume with the piston at bottom dead center. If cylinder volume with the piston at bottom dead center is 10 times more than it is with the piston at top dead center, then we have a compression ratio of 10.0:1, or simply 10 to 1. It is the proverbial ten pounds of fertilizer in a one-pound bag, not that we would be inclined to show you an example.
Five basic facts affect compression ratio. Cylinder swept volume, piston dome shape, head gasket thickness, clearance volume, and combustion chamber size. Swept volume is how much air or volume the piston displaces during its journey to the top of the bore. If we enlarge the swept volume by boring the cylinder oversize or increasing stroke, we increase compression ratio.
We may also increase or decrease compression ratio by changing the piston dome. If we dish the top of the piston, we lose compression. This is common with stock pistons that are often dished to reduce compression. A good example is a the 289-2V and 4V engines from 1965-67. The 289-2V cast piston is dished to keep the compression around 9.0:1. The 289-4V engine has a flat-top piston to increase compression to 10.0:1. The same is true for the 289 High Performance V-8. Latemodel 5.0L High Output engines sport compression ratios of 10.0:1 with flattop pistons and valve reliefs.
To raise compression ratio, we can dome the piston, with a surface shaped like the combustion chamber. This reduces clearance volume at the top of the bore. When we reduce clearance volume, we increase compression ratio.
Compression ratio may also be increased by reducing combustion chamber size. For example, older 289/302/351W heads have smaller chambers, which means plenty of compression with a stroker kit. While this has its power benefits, it also can cause engine damage and destruction. A 347ci stroker kit with a 289’s 57cc chambers can yield too much compression, and with catastrophic results. For one thing, a 289 head wouldn’t be an intelligent choice for a 347ci stroker. Port size would greatly limit the engine’s potential. This leads us to a better aftermarket cylinder head for the 347. And don’t discount the 351W head for your 347ci stroker either. It makes for a stealthy factory cylinder head for the 347.
Whenever you step up to an aftermarket head, keep combustion chamber size in mind. Most aftermarket heads have chamber sizes around 64cc. If you desire greater compression, you can make adjustments with proper piston selection.
Cylinder volume is figured using a simple formula. Using a standard 351W or 351C bore and stroke (4.00 x 3.50 inches), work the following numbers.
Cylinder Volume = 0.7853982 x Bore x Bore x Stroke
When we apply this formula, we come up with 43.982ci per cylinder. Multiply this number by eight and you have 351ci. Truth is, you have 351.858, which is closer to 352ci. If we bore the 351 to 4.030-inches, we then have 44.644ci per cylinder, which comes out to 357ci. See the accompanying table for easy answers.
If we take a standard 4.000-inch bore and overbore it by .030-inch to 4.030- inch, compression will increase by a fraction of a compression ratio point. If we have compression ratio of 10.0:1, compression will increase by less than a point with a .030-inch overbore. We compute the compression increase (or decrease) by figuring the clearance volume, which is the area left above the piston when it reaches top dead center. It is important to understand that the piston doesn’t always reach top dead center flush with the block deck. In most applications, the piston comes within 0.005 to 0.020-inch below the deck surface. It looks more flush with the block deck than it actually is. This is called piston deck height. Piston deck height affects compression because it determines clearance volume at the top. If we have a lot of clearance volume, we have less compression. The greater the piston deck height, the lower the compression ratio.
The following is a formula for figuring clearance volume.
Clearance Volume = 0.7853982 x Bore x Bore x Deck Height
Again, let’s look at our 351ci smallblock with a 4.000-inch bore and 3.50- inch stroke. Let’s say our 351 has a piston deck height of 0.015-inch below the block deck. When we use our formula of 0.7853982 x 4.000” x 4.000” x 0.015”, we get 0.188ci, or just a fraction of the cylinder’s 43.98ci. If the deck height increased any amount, compression would drop. If deck height decreased any amount, compression would increase.
After figuring how to compute displacement in each cylinder and how to figure in the effect of piston deck height on compression, it’s time to figure in the piston’s role in all of this. Remember that if we dish the piston, we lose compression. If we dome the piston, we increase compression. Most piston manufacturers will give you the specifications on a pis ton. If it is dished, the manufacturer will tell you how much. Likewise for a domed piston. This is performed in cubic-centimeters (cc’s). How many cc’s are in the dish? How many cc’s of volume are in the dome?
If you are baffled by cubic-centimeters versus cubic inches, you’re not alone. A lot of us are confused by metric versus SAE. Follow this formula and end your confusion.
Cubic Inches = cc’s x 0.0610237
Back to our 351ci engine. Lets say our 351 has dished pistons with 4.00cc dishes. Using our formula, we multiply 4cc times 0.0610237, which equals 0.244ci. This lowers compression ratio because we have more clearance volume above the piston. If we dome the piston by the same amount, we increase compression accordingly.
The next factor in compression ratio is cylinder head gasket volume, which contributes to clearance volume above the piston. The thickness of the head gasket affects compression ratio. The thicker the head gasket, the greater the clearance volume. This lowers compression. The thinner the head gasket, the lower the clearance volume, which increases compression. To figure the head gasket volume (displacement), use the following formula.
Cylinder Head Gasket Volume/Thickness = 0.7853982 x Gasket Bore x Gasket Bore x Compressed Thickness
Again our 351ci engine with a 4.000- inch bore. We have a cylinder head gasket that is 0.040-inch thick. We take 0.7853982 x 4.000” x 4.000” x 0.040” to arrive at 0.502ci of clearance volume.
With all of these issues out of the way, it’s time to focus on combustion chamber volume. Combustion chamber volume is the actual size of the chamber in cubic-centimeters (cc’s). Think of the combustion chamber as the ultimate clearance volume. Chamber sizes for small-block Fords (289/302/351W) range from 53cc to 64cc. For the 351C/351M/400M, chamber sizes run much larger. The 351C-4V head has small wedge chambers. The 351C-2V, 351M and 400M head has larger open chambers.
Combustion chamber volume is figured with a graduate scale using fluid. We meter fluid into the chamber and figure how much fluid is used. We get this figure in cubic-centimeters. Our sample cylinder head has 64cc chambers. Here’s how we turn cubic-centimeters into cubic inches.
Combustion Chamber cc’s x 0.0610237 = Combustion Chamber ci’s
Based on our formula above at 64cc, we have 3.90ci of volume in the chamber alone. Now, we have all of the information needed to compute compression ratio in our 351ci engine. Add up all of the numbers for bore and stroke, piston deck height, head gasket thickness, and combustion chamber size. Use the following formula.
Cylinder Vol. + Clearance Vol. + Piston Vol. + Chamber Vol. + Gasket Vol. / Clearance Vol. + Piston Vol. + Head Gasket Vol. + Chamber Vol. = Compression Ratio
Our 351ci engine, with its 4.00-inch bores and 3.50-inch stroke, 0.020-inch deck height, 0.040-inch head gasket thickness, 64cc chamber heads, and 4.00cc dished pistons winds up like this.
43.982ci + 0.188ci + 0.244ci + 3.90ci + 0.502ci / 188ci + 0.244ci + 0.502ci + 3.90ci = 10.10:1
When we work this formula, we are taking cylinder volume, clearance volume, piston volume, chamber volume and gasket volume, and adding them together to arrive at 48.816ci. Then we add up clearance volume, piston volume, head gasket volume and chamber volume to get 4.834ci. Then, we take 48.816ci and divide it by 4.834ci to arrive at 10.098, which, rounded off to the nearest tenth, is 10.10:1.
HORSEPOWER & TORQUE
We’ve long been led to believe horsepower is what power is all about. But horsepower is rooted more in Madison Avenue advertising rhetoric than fact. In the power picture, horsepower doesn’t count for much. What counts most is torque, and where in the rev range our engine makes the most of it. The truth is, engines make torque when we feed fuel and air into combustion chambers and squeeze the mix. A good friend of ours, John Baechtel of Westech Performance in Ontario, California, said it best when he said, “Torque is the grunt that gets us going, and horsepower is the force that keeps us moving…” Well said, John, and oh so very true.
Engines are doing their best work when they reach peak torque, where they are making the most grunt. John tells us that when an engine is below the torque peak, it has more than enough time to completely fill the cylinder with air and fuel. He adds that when engine RPM rises above the torque peak, there isn’t enough time to completely fill the cylinders with air and fuel.
The power we feel from an engine’s spinning crankshaft is torque multiplied by engine speed (RPM) to produce a number that tells us something about the engine’s output. This theory dates back to steam engines and an inventor named James Watt. Watt invented the steam engine long ago in the 1800s. Watt’s theory was a simple one. It compared the work his steam engine could do with the same work an equal number of horses could do. Watt determined a single horse could pull a 180-pound load 181 feet in one minute’s time. This formula figured out to 32,580 lbs/ft per minute. Watt rounded it off to 33,000 lbs/ft per minute. He divided this figure by 60 seconds, which worked out to 550 lbs/ft per second. And this became the standard for one horsepower.
As a result of Watt’s calculations long ago, horsepower has become a measure of force in pounds against a distance in feet for the brief period of one minute. Then, we take this formula and apply it to an engine’s crankshaft at each journal throw to arrive at horsepower. This is based on the number 5252.
Torque and RPM are divided by 5252. And torque and horsepower always equal at 5252. If you are able to solve this equation at 5,252 rpm, RPM cancels out, ultimately leaving horsepower equal to the torque figure. In fact, if you work this out on a graph, the torque, horsepower and RPM lines should always intersect.
When we look at torque alone, it is the measure of an engine’s work. Horsepower is a measure of how quickly the engine does the work. Torque comes mostly from displacement and stroke. This means the real power we derive from an engine comes in the torque curve. The broader the torque curve, the better our power package. A broader torque curve comes from making the most of the fuel/air mixture across a broader RPM range. This is best accomplished with a longer stroke and a larger bore. And this is what strokers are all about. Strokers are about making the most torque across the broadest range. Truth is, we’re never going to get the best of everything, even with fuel-injected engines. Our engines need to be planned and built based on the way we’re going to use them. What we choose in terms of a camshaft, cylinder heads, and induction system determines how our engine will perform.
Other Power Considerations
When we’re planning for power, we rarely stop to consider how power gets wasted in an engine’s design and construction. Friction is the power pick-pocket hiding in all sorts of placed inside our engines. Most of the friction occurs at the pistons and rings. Some of it gets lost at the bearings and journals. Yet more of it gets consumed at piston wrist pins, lifters and bores, cam lobes and lifters, rocker arm fulcrums, and valvestems.
Our mission during the engine build needs to be finding a compromise between having tolerances that are too loose and too tight. Piston-to-cylinder-wall clearances are critical in order to have good cylinder sealing without too much friction and drag. The same is true for rod and main bearing clearances. Another power-tap issue is engine breathing. You want an induction system that helps your engine breathe well at the RPM range it is designed and built for. This means the appropriate intake manifold and carburetor. Go too small on carburetor sizing, and you restrict breathing. If ports don’t match in terms of size, you restrict breathing. Opt for cylinder heads where port sizing is too limited for your displacement and you restrict breathing. One example would be stock 289/302 heads on a 355ci stroker. This brings compression to mind immediately. Run too much compression and you kill power with detonation.
On the exhaust side, you want a scavenging system that makes sense. You don’t have to have long-tube headers for great breathing. Shorty headers will do the job just as well, and without the shortcomings of long-tube headers. Go too large on header tube size and you hurt torque. Go too small and you hurt power on the high end. This is where your exhaust system has to work hand-in-hand with the heads, camshaft, and induction system.
Quick Power With Nitrous Oxide
Nitrous oxide, or “squeeze,” is popular today for those looking for quick and easy power (50 to 150 horsepower) on demand. It makes boatloads of power at the touch of a button, but nitrous can be very harmful to an engine that isn’t properly prepared and tuned. Nitrous will severely damage your pistons and rings if it is not used properly. It can and does hammer rod bearings, resulting in severe wear. It is also hard on main bearings due to these severe loads. And no matter what the nitrous oxide optimist club will tell you about laughing gas, nitrous can and does shorten engine life. So don’t be drawn into believing it’s a magic horsepower pill without consequences. If you’re going to be using nitrous oxide, be prepared for its shortcomings. Accept the fact that nitrous will shorten engine life no matter how it is used. The more aggressively you use nitrous, the shorter your engine will live.
So what, exactly, is nitrous oxide, and what does it do? Nitrous is a physics lesson in how to generate greater amounts of power from the fuel/air charge we introduce to the combustion chambers. Nitrous Oxide is a very simple gas composed of two nitrogen atoms attached to one oxygen atom. Chemists call it N2O. Contrary to what you may believe about N2O, it is not a poisonous gas, nor is it harmful to the atmosphere. This doesn’t mean you should breathe it, however. Because N2O is an asphyxiant, it can suffocate you if inhaled in heavy quantities. It would have a similar affect on you as carbon dioxide (CO2), called oxygen deprivation.
Nitrous Oxide is available in three basic grades: medical, commercial, and high-purity. The medical grade is what’s commonly known as “laughing gas,” which used by dentists and surgeons. It has to be very pure for human consumption. You must be licensed as a medical professional to get it. Commercial grade nitrous oxide is what we use in our engines for performance gains. High-purity is also a medical grade nitrous oxide that is extremely pure, resulting in it being priced and controlled accordingly.
The commercial grade nitrous oxide is marketed as Nytrous+ and sold by the Puritan-Bennett Corporation. You can find it all across the country. It is a mix of 99.9% nitrous oxide and 0.01% sulfur dioxide. Puritan-Bennett adds the sulfur dioxide to give its N2O gas odor just like we experience with natural gas.
When you buy nitrous oxide, it is pumped into a storage tank that you provide the supplier. You need an appropriate tank capable of holding at least 1,800 pounds per square inch (psi). To play it safe, your tank(s) must have a visible certification date from within the past five years. Inside the tank, nitrous oxide exists in liquid form. As it leaves the tank, it becomes a gas. When it leaves the tank quickly, it leaves very cold, just like refrigerants and propane. To be a liquid, there has to be enough pressure inside the tank to turn the nitrous oxide into a liquid. Unpressurized, nitrous oxide exists as a gas. For nitrous oxide to become a liquid in an unpressurized environment, the ambient temperature has to be –127 degrees F. At 70 degrees F, nitrous oxide needs to be pressurized to 760 psi to become a liquid. Warm things up to 80 degrees F and you need 865 psi to make nitrous oxide a liquid.
The use of nitrous oxide to make power is nothing new. In World War II, it was used to help aircraft engines make more power. The principle then was much the same as it is now. Nitrous oxide was stored under pressure in tanks. Nitrous oxide stored under pressure must be anchored securely in the interest of safety. We stress safety because a carelessly handled nitrous oxide bottle with nearly 1,000 psi of pressure behaves like a bomb if the bottle fails. It can explode, maiming or killing you.
To get the nitrous we need for performance use on demand, we meter this gas from the bottle via electrical solenoids that are fired when we hit the button. Of course, it involves more than this. Nitrous oxide should be administered on demand at a time when it is safe to do so. Too much nitrous oxide and not enough fuel can destroy an engine. For one thing, nitrous oxide should never be administered to the intake ports unless the throttle is wide open. Set up properly, the throttle should close a nitrous oxide solenoid switch when in the wideopen position. Closing the switch activates the nitrous oxide solenoid, releasing the nitrous oxide into the intake manifold.
So how do we get nitrous oxide into the intake ports? We do it a number of ways, depending on how the engine is set up. Carbureted engines get their nitrous oxide diet through a fogger plate located beneath the carburetor. Pin the butterflies and the nitrous oxide fogs the intake plenum, adding to the fuel/air mixture en route to the chambers. Carbureted engines may also use nozzles at each intake port to administer the nitrous oxide. The nice part about this design is being able to tune each cylinder bore based on the needs of that cylinder. On carbureted engines, the center ports typically receive more fuel and air than the perimeter ports. The outers tend to run more lean than the centers, which is very critical when you are running nitrous oxide.
Port fuel-injected engines also use nozzles off of a common tube manifold to administer nitrous oxide at each port. Like its carbureted counterpart, the port-injected nitrous oxide arrangement can be porttuned for better performance. This is especially true when you think of your V-8 engine as eight separate engines operating on a common crankshaft.
One popular misconception is that we get power from the nitrous oxide itself. But this isn’t true. Nitrous oxide works hand-inhand with the fuel/air mix to make power in each cylinder bore. Nitrous oxide brings out the best in the fuel. Not only is the nitrous oxide mist cold (good for thermal expansion), it is also loaded with oxygen, which gives the igniting fuel/air mix a bad attitude. It makes the fuel/air mix burn faster, which creates a powerful thermal expansion experience in each combustion chamber
Where we have to be careful with nitrous oxide is how we feed it to our engines. Perhaps this isn’t the best parallel, but nitrous oxide has to be thought of the same way you would cocaine, crystal meth’, or nicotine. The more powerful the nitrous oxide experience, the more an enthusiast wants. So we keep feeding our engine more and more nitrous oxide in our quest for power, until it fails under the stress. You must recognize your engine’s limits before even getting started on a nitrous oxide diet.
WORKING WITH NITROUS OXIDE
The first thing to remember with nitrous oxide is that it makes fuel burn faster. This means you must be mindful of what it can do, both productively and counterproductively. All that instantaneous power comes for a reason. As a result, extraordinary attention to detail must be paid on the road to power.
Lets start with engine tuning. Administering nitrous oxide to the combustion chambers should not be done with reckless abandon. Use too much of it and you burn pistons. You have to think of nitrous oxide and your air/fuel mixture just like you would oxygen and acetylene. When we’re using oxygen and acetylene to weld or cut steel, we use lots of oxygen to blaze a path through the steel. The same can happen inside your engine when we use too much nitrous oxide. You can burn right through the piston like a cutting torch. And aluminum pistons aren’t as forgiving, they melt at 1300 degrees F.
When we are tuning a small-block Ford to run on nitrous oxide, we have to get fuel/air mixture and spark timing where they need to be or face certain destruction. So how do we get there? First, we have to control fuel delivery to where it jibes with the flow of nitrous oxide. If we get too much N2O and not enough fuel, we overheat the chamber and melt pistons. This means we have to control fuel and nitrous oxide flow to a finite point where we get the most power possible without doing engine damage. This takes practice.
The key to getting the most power from nitrous oxide is getting spark timing, fuel delivery, and peak cylinder pressure going at the same time. Ideally, we light the fuel/air/nitrous mixture at the time when we have peak cylinder pressure, which makes the most of the incoming charge. When everything is working well together, we get a smooth, firm light-off that nets us a lot of power. Things go wrong when the light-off resembles an explosion, exerting a shockwave on the top of the piston. This is the spark knock we hear as a multiple rapping under acceleration.
When fuel, air, and nitrous ignite violently, why don’t we net more power from the explosion? The answer is simple. When an engine is running smoothly, we get that quick-fire mentioned earlier in this chapter. A smooth light-off applies pressure to the piston dome, forcing it downward in the cylinder bore, turning the crank and completing the power stroke. Detonation is what occurs when we get a spontaneous light-off, especially from two points in the chamber. The two waves of power collide, causing spark knock or pinging under acceleration. The problem with this kind of light-off is that those violent combustion spikes don’t really yield much power.
So how do we safely make the most of nitrous oxide? We should first address the fuel system because we need to have enough fuel to meet the demands of nitrous oxide. Without enough fuel, we toast the engine. The next issue is fuel octane rating. You need to decide what octane rating you expect to use. Next is ignition timing. Where does yours need to be? And finally, too much compression with nitrous will cause destructive detonation. Getting each of these elements dialed in is crucial to productive performance.
Compression has to be thought of two ways – static and dynamic. Static compression is the compression ratio we often think of. This is the swept volume above the piston, with the piston at bottom dead center, versus the clearance volume left when the piston is at top dead center. If we have 100cc of volume with the piston at bottom dead center and 10cc left with the piston at top dead center, then we have a static compression ratio of 10.0:1 – 100cc to 10cc.
Dynamic compression is what happens with the engine operating. This is the kind of compression that happens with pistons, valves, and gasses in motion through the engine. We get dynamic compression when we are huffing lung-fulls of air through the engine during operation. With the engine running, we are pumping more volume through the cylinders and chambers than we would simply hand-cranking the engine. This actually increases the compression ratio, which means dynamic compression is higher than static compression. This means you need to consider the dynamic compression ratio as your engine’s actual compression figure when you’re planning nitrous oxide.
With the issue of compression out of the way, we will address camshaft selection when using nitrous oxide. Nitrous-burning engines need different camshafts than those that are naturally aspirated or supercharged. Dynamic compression ratio, mentioned earlier, is affected by camshaft profile. A camshaft profile with a short duration will give us greater dynamic compression. When we lengthen the duration, we tend to lose dynamic compression.
On the exhaust side, duration is a very important issue with nitrous. Because the fuel/air/nitrous charge coming in expands with fury during ignition, it needs a way to escape when the exhaust valve opens. We need a longer exhaust valve duration with nitrous for good scavenging and thorough extraction of power. While we’re thinking about exhaust valve duration, we must also remember overlap in all of this. Less overlap equals more dynamic compression. More overlap equals less dynamic compression. Overlap is that process in the power cycle where the exhaust valve is closing and the intake valve is opening. The incoming charge helps scavenge the outgoing hot gasses through the overlap process. What this means is simple. It means the exhaust valve needs to open earlier in the cycle and stay open longer for adequate scavenging.
Fuel octane plays into the power process because we need to understand when and how the fuel will ignite. The higher the fuel octane rating, the more slowly it ignites and burns, which reduces the chances of detonation and pre-ignition. With a higher octane rating, we get a smooth, more predictable light-off in the chamber. When we opt for a lower fuel octane rating, we get a more unstable fuel that will light quickly and causing pinging. When we throw nitrous oxide into the equation, we can count on a quick light that can be violent in nature. This is why a higher octane rating is so critical to a cohesive performance package.
With the issues of fuel octane and compression behind us, we’re ready to address the all-important air/fuel mixture. This is called the air/fuel ratio. We do this by adjusting jet size in the carburetor or controlling fuel injector pulse width. Jet size and pulse width both determine how much fuel we’re going to throw in the chamber. If your tuning effort involves a carburetor, you have to get jet sizing down to a science that will help your engine live on nitrous oxide. As a rule, carbureted engines live happily with an air/fuel ratio of 12.5:1 to 13.0:1. This is where we have just the right amount of air and fuel to make power. If we go any leaner, we can cause engine damage. We will also lose power. Any richer and we lose power as well.
When we’re working with fuel-injected engines, we can control fuel mixture by reprogramming the electronic control module or changing injector size. With nitrous, we typically go up on injector size and fine tune from there. Too large is better than too small. Factory fuel injection systems run a fuel manifold pressure of 30-45 psi. If you’re running nitrous oxide, you’re going to need a lot more fuel pressure to get the job done safely. Around 80 psi is considered the norm for nitrous oxide and electronic fuel injection. This is when you need to step up to high-pressure Earl’s hoses and fittings.
Ignition timing is the next big hurdle because it can kill an engine as quickly as a lean fuel mixture or too much compression when we’re running nitrous. We want the spark to occur in advance of peak cylinder pressure because it takes time for the fuel/air/nitrous mixture to ignite. Under normal circumstances, without nitrous, we want full spark advance around 36 to 41 degrees before top dead center. Exactly where the spark occurs depends on how the engine is equipped and how it performs at full spark advance at 3,500 rpm. Because each and every engine is different, full advance is going to vary from engine to engine.
When we throw nitrous oxide into the equation, we have an air/fuel/nitrous mixture that is going to ignite more rapidly than the conventional fuel/air mix. The pros suggest retarding the ignition timing to approximately 12 degrees BTDC because the air/fuel/nitrous mixture ignites much more quickly. With the full spark advance at 36- 41 degrees BTDC, we would waste the engine in short order. Retard timing to 12 degrees BTDC and go from there. Twelve degrees BTDC at 3,500 rpm needs to be your baseline, then slowly advance ignition timing from there. Test it out at wide-open throttle under a load, beginning at 12 degrees BTDC, then advance from there one degree at a time.
With the basics out of the way, there are other points to consider when running nitrous. To be effective, fuel has to atomize (vaporize) properly. This means the fuel has to mist as it enters the intake manifold and, ultimately, the combustion chamber. Problem here is, nitrous comes out of the fogger or nozzle ice cold. This makes it very difficult to atomize the fuel effectively. When nitrous comes out of the fogger or nozzle at a frigid –100 degrees F, fuel tends to exist as large droplets, rather than the mist we need for good ignition and combustion.
Nitrous oxide system manufacturers have dealt effectively with the issue of fuel atomization by designing systems that allow the gasoline to atomize with the nitrous oxide fog or mist. The finer we can get the mist, the more power we’re going to pull from the mixture. So, the objective is to keep the fuel in suspension as long as possible.
HOW MUCH FUEL?
There is a formula that will make it easier to prepare your fuel system for nitrous operation. The air to fuel ratio in a naturally aspirated engine should be between 12.5:1 and 13.0:1. This is a range where engines are happiest and make the most power. Things change dramatically when we introduce nitrous oxide to the air/fuel mixture. We need way more fuel to both make power and prevent engine damage.
Most nitrous experts we have consulted suggest a nitrous to fuel ratio of 5.0:1 as a starting point for engine tuning. Starting here means going decidedly rich, but it’s the safest approach going. Begin at 5.0:1 and steer your tuning toward 6.0:1 for optimum results. If your power goal is, for example, 500 horsepower on nitrous oxide, you’re going to need 37.94 gallons an hour or 0.63 gallons a minute to run happily on nitrous oxide. Obviously, we’re not going to stay on nitrous oxide for one hour, but it gives you a good idea about how much fuel you’re going to need.
CarTech Books publishes an excellent nitrous oxide book (SA-50), authored by respected and well-known automotive writer, Joe Pettitt. For more detailed information on nitrous oxide, pick up this book at your favorite bookstore.
MAKING REAL STROKER POWER
There are plenty of myths about making power, especially in the Ford camp. Folklore tells us it’s easier to make power with a Chevrolet than a Ford. But this is pure nonsense. You can make just as much power with a Ford for the same amount of money you can a Chevrolet. What gives the Chevrolet an advantage is numbers. Chevys are simply more commonplace than Ford. But even this is changing because Ford’s popularity has grown dramatically in recent years. When it comes to seat-ofthe-pants performance, there’s no black magic here, just the simple physics of taking thermal expansion and turning it into rotary motion.
To learn how to make power, we have to understand how power is made inside an engine to begin with. How much power an engine makes depends on how much air and fuel we can pump through the engine, plus what we do with that fuel and air mixture during that split-second it lives and dies in the combustion chambers.
We have to think of an internal combustion engine as an air pump. The more air and fuel we can pump through the cylinders, the more power we’re going to make. This is why racers use big carburetors, manifolds, heads, superchargers, turbochargers, and nitrous oxide. Racers understand this air pump theory and practice it with reckless abandon, – sometimes with catastrophic results. But good racers also understand the too much of a good thing theory. Sometimes it can cost you a race – sometimes an engine.
Getting power from our air pump takes getting liberal amounts of air and fuel into the chambers, then squeezing the mixture as hard as we can without damaging the engine. When we raise compression, we increase the power our mixture yields. It is the intense heat of compression coupled with the ignition system spark that launch the yield of energy from our mixture. The more compression we have, the greater the heat we have to ignite the mixture.
Problem is, when there’s too much compression and the resulting heat, the air/fuel mixture can ignite prematurely resulting in pre-ignition and detonation. So we have to achieve the right compression ratio to get the most from the fuel we have. Today’s street fuels won’t tolerate much over 10.0:1 compression. This means we have to look elsewhere for answers in the power equation, like more aggressive camshaft profiles, better heads, port work, hotter ignition systems, exhaust headers that breathe better, stateof-the-art intake manifolds and carburetors, even electronic fuel injection where we never thought of using it before. The thing to remember about gasoline engines is this: The fuel/air mixture does not explode in the combustion chambers, it lights off just like your gas furnace or water heater. Because the mixture is compressed and ignited, it lights-off more rapidly. Combustion in a piston engine is just that, a quick fire that sends a flame front across the top of the piston. Under ideal circumstances, the flame front will travel smoothly across the piston dome, yielding heat and pressure that act on the piston and rod uniformly to create rotary motion at the crankshaft.
A bad light-off that originates at two opposing points in the chamber is pre-ignition or detonation, which we were talking about earlier. The opposing light-offs collide creating a shock that hammers the piston dome, which is the pinging or spark knock we hear under acceleration. The objective is to get a smooth, quick fire, with the flame front traveling in one direction for maximum power. Call this power management. Power management is having the right balance of ignition timing, fuel mixture, compression ratio, valve timing events, and even external forces like blower boost or nitrous input. All of these elements have to work together if we’re going to make productive power. Let’s talk about some of the elements we need to make power.
For one thing, the science of making power must tie in with your intended vehicle usage. And that’s where most of us get it wrong all too often. In our quest for stroker torque, we sometimes forget how the vehicle is going to be driven and used. If you are building a stroker to go drag racing, the way you build your engine is going to be different than the guy who builds one for trailer towing. By the same token, road racing engines should be constructed differently than drag racing powerplants.
So how do we approach each engine’s mission? Street engines for the daily commute need to be designed for good low and mid-range torque. Drag racing engines need to make power at mid to high-RPM ranges. Road racing engines need to be able to do it all – down low, in the middle, and at high RPM – because they’re going to be in all of these ranges while racing. Engines scheduled for trailer towing need plenty of low-end torque. They also need to be able to live comfortably at mid-range, when we’re going to be pulling up a grade.
One More Thing …
Anytime you’re going to raise your engine’s stress level by using nitrous oxide, supercharging, or turbocharging, you should remember the importance of cylinder sealing. Opt for only the best competition head gaskets you can find. Be prepared to spend more than $100.00 for a set. If you’re going to blow a ton of squeeze or boost into the chambers, think seriously about Oringing the block for adequate cylinder sealing.
CAMSHAFT & VALVETRAIN BASICS
The camshaft and valvetrain directly determine not only an engine’s personality, but how reliably an engine will perform throughout its service life. When it comes to camshafts, there are probably more misconceptions then there are facts. We’re here to dissolve most of the myths and get you headed in the right direction on your stroker project. To understand how to pick a camshaft and valvetrain, you must first understand how it all works. Choosing a camshaft profile is rooted in how we want an engine to perform. Are we building a streetable stroker where low and mid-range torque are important, or are we building a high-revving racing engine that makes peak torque in the high revs?
A camshaft manufacturer’s catalog lists dozens of camshaft types for the same type of engine. This is where it gets mighty confusing for the novice. We see words like lift, duration, lobe separation, base circle, lobe centerline angle, and valve overlap. It is important to know what this information means and how will it affect your engine’s performance.
Camshaft Shop Talk
What separates one camshaft from another is called profile. Profile is lobe design, dimension and positioning, when it opens the valve, when it closes the valve, how long it keeps the valve open, and how much it opens the valve. All of these factors play into how the engine will perform.
Lift is the maximum distance that a camshaft lobe will open a valve. Duration is how long the lobe will keep the valve open. Lobe Separation or centerline is the time or duration between intake and exhaust valve action. Overlap plays into lobe separation because it is the period when the exhaust valve is closing and the intake valve is opening. The Ramp is the ascending or descending side of the cam lobe coming off the base circle when lift begins to occur. Flank is the ascending or descending portion of the lobe past the base circle nearest maximum lift. The camshaft’s Base Circle is the portion of the lobe that doesn’t generate lift. The bottom-most portion of the lobe is called the Heel.
Flat tappet camshafts work differently than roller tappet camshafts, which means we have to think differently with each type. Flat tappet camshafts limit what we can do with lobe profile if we want streetability. If we want an aggressive profile with flat tappets, we can only go so far with a street engine, or suffer with poor drivability (rough idle and low manifold vacuum). If you want an aggressive profile in a street engine, we suggest stepping up to a roller camshaft, which can handle the aggressive profile better using roller tappets.
Supercharging, like nitrous oxide injection, was conceived of a long time ago to extract as much power as possible from a given displacement. Unlike nitrous oxide, supercharging is more involved, yet easier to tune and manage. It is easier to tune because you know you’re getting into trouble before getting there. Knowing you’re in trouble comes from the sound of detonation. Superchargers and turbochargers don’t come on as strong as quickly as nitrous. For the most part, they cannot damage the engine as quickly as nitrous, because you can come off the power in time to prevent engine damage. There is also a safety device, called a wastegate, designed to prevent excessive boost with superchargers and turbochargers. With nitrous oxide, damage and certain engine death are instantaneous if you deliver too much of it without enough fuel, or with too much ignition timing.
Supercharging and turbocharging both accomplish the same objective. They each force air into the cylinders to make the most of a combustion power cycle. They mechanically increase cylinder pressure , which, given enough fuel, makes more power. Superchargers are driven by the engine’s crankshaft. Turbochargers are driven by exhaust gas pressure. A supercharger’s compressor, driven by the crankshaft, moves the air we’re feeding into the intake manifold. A turbocharger’s compressor, driven by exhaust gas pressure, does the same thing.
Superchargers give engine nearly immediate power. The power comes on stronger with RPMs. With the increase in RPMs, the compressor turns faster, forcing more air pressure into the intake manifold, which gives us the power. We prevent overpressure by fitting the supercharger with a wastegate, which vents excessive pressure. Turbochargers take a certain amount of time to give us induction pressure when we step on the gas. This is called turbo lag. Since it takes the turbocharger time to spool up during acceleration, there is a certain amount of lag before we get the boost or pressure, and the resulting power. Turbochargers have a wastegate, which also bleeds excessive boost pressure and prevents engine damage.
There are six basic different types of superchargers: centrifugal, rotary, axial flow, Roots two and three-lobe, vane type, and Lysholm screw. Probably the most common type we see out there on small and middle-block Fords are centrifugal and Roots blowers. Centrifugal types are typically hung on the front of the engine, driven by the crankshaft pulley. Roots blowers, also driven by the crankshaft pulley, are normally an integral part of the intake manifold, with the carburetor mounted immediately upwind of the blower. With fuel injection, the throttle body is mounted in any number of locations before the Roots blower’s intake. Fuel injectors are positioned in each of the intake ports, downwind of the Roots blower.
Which type of supercharger should you choose and why? This is hard to answer because everyone has different expectations and needs. Which supercharger you choose is going to depend on your needs. Roots and centrifugal superchargers both have significant purposes. We choose the Roots blower for different purposes than we choose a centrifugal huffer. Lets talk about the Roots blower first.
The Roots lobe-type supercharger has served many purposes during its service lifetime. Probably the most common Roots supercharger duty has been to feed hungry Detroit two-stroke diesel engines. You’ve undoubtedly heard the term “6-71 blower” in hot-rodding circles. Detroit two-stroke diesel engines, once manufactured by General Motors, are named based on displacement, number of cylinders and cylinder arrangement. The Detroit 6V-71, for example, is a V-6, with 71 cubic inches of displacement per cylinder. A Detroit 8V-92 is a V-8, with 92 cubic inches per cylinder. The Detroit 6-71 is an in-line six, with 71 cubic inches per cylinder. So when you see a huge 6-71 blower atop a well-fed small-block Ford, it’s a blower originally designed for huge, heavy-duty Detroit diesels that power semi-trucks. Detroit two-cycle diesel engines have been in steady service since the 1930s. They’re smoky and noisy. You’ve probably seen untold thousands of them over your lifetime in city busses, heavy trucks, fire trucks, stationary water pumping stations, and hundreds of other places. Since they are a two-stroke design, they fire on every revolution of the crankshaft, which makes them real screamers.
What makes a Roots blower effective is its positive displacement design, which a Detroit two-stroke diesel engine needs for proper ingestion of air and scavenging of exhaust gasses. This kind of positive displacement design provides plenty of cylinder pressure when and where it counts in a high-performance V-8 engine.
We speak of positive displacement when discussing Roots blowers because their very design doesn’t allow much, if any air to escape en route to the chambers. Roots blowers have two and three-lobe rotor designs where rotors interlock to ensure consistent airflow into the engine.
Ford has been using the Roots design on factory production engines for many years, beginning with the 1989 3.8L Essex V-6 Thunderbird. Today, it is used atop the 5.4L SOHC V-8 engine in the Lightning and Harley-Davidson F-150 trucks, for example. This reliable, highly successful supercharger will work quite well on your small-block Ford.
A more common type of supercharger is the centrifugal type we see and hear at a lot of Ford events on newer 5.0L and 4.6L Mustangs. It’s that familiar whistle associated mostly with the Vortech and Paxton superchargers. Instead of the interlocking rotors used in the Roots positive displacement supercharger, centrifugal superchargers employ a fan that draws air into its center and rings it outward into a duct where it enters the intake manifold. Centrifugal force is defined by The American Heritage Dictionary as “the component of an apparent force or a body in curvilinear motion, as observed from that body, that is directed away from a curvature or axis of rotation.”
To make this easier to understand, centrifugal force is the energy of a spinning object that tends to throw the object, or parts of the object outward. In this case, air is the object we sling outward from the spinning fan (compressor). The compressor takes the air in through its center and blows it outward with the whirling blades or fins that thrust it outward into the shell into the intake tube. Not only does the compressor move the air outward from its center, it also squeezes the air in the shell, feeding it to the intake tube. Think of the centrifugal style blower like your hairdryer where air is drawn into one side and blown out the other side. A hairdryer is a compressor of sorts. Even the humble blower in your Ford’s air conditioning system compresses air to some degree before it exits your dashboard outlets. Even your home vacuum cleaner has a compressor, most of which are of a centrifugal blower design. The best vacuum cleaner example we can think of is an old-fashioned Kirby upright vacuum cleaner with a centrifugal blower.
Turbochargers are like the centrifugal supercharger because they work much the same way. Instead of being belt-driven, they’re driven by a turbine that is propelled by hot exhaust gasses. As we accelerate, hot exhaust gasses drive the turbocharger’s single-stage turbine, which drives the centrifugal compressor.
Street Cam Facts
Based on everything we’ve seen in 50 years of experience, the best street performance cams are ground with a lobe separation between 108 to 114 degrees. When we keep lobe separation above 112 degrees, we improve drivability because the engine idles smoother and makes better low-end torque. This is what we want from a street engine. Any time lobe separation is below 108 degrees, idle quality and streetability suffer. But there’s more to it than just lobe separation.
Compression and cam timing must be considered together because one always affects the other. Valve timing events directly affect cylinder pressure. Long intake valve duration reduces cylinder pressure. Shorter duration increases cylinder pressure. Too much cylinder pressure can cause detonation (pinging). Too little and you lose torque. You can count on cam manufacturers to figure stock compression ratios into their camshaft selection tables, which makes choosing a camshaft easier than it’s ever been. Plug your application into the equation and you will be pleased with the result most of the time.
The greatest advice we can offer the novice is to be conservative with your cam specs if you want reliability and an engine that will live a long time. Keep with a conservative lift profile (under .500 inch). High-lift camshafts beat the daylights out of a valvetrain. And they put valve to piston clearances at risk. Watch duration and lobe separation closely, which will help you be more effective in camshaft selection. Instead of opening the valve more (lift), we want to open it longer (duration) and in better efficiency with piston timing (overlap or lobe separation).
Always keep in mind what you’re going to have for induction, heads, and exhaust. The savvy engine builder understands that in order to work effectively, an engine must have matched components. Cam, valvetrain, heads, intake manifold, and an exhaust system must all work as a team or you’re just wasting time and money. If you’re going to use stock heads, which we expect with a budget stroker engine, your cam profile need not be too aggressive. Opt for a cam profile that will give you good low and mid-range torque. Torque doesn’t do you any good on the street when it happens at 6500 rpm. Choose a cam profile that will make good torque between 2500 and 4500 rpm. Otherwise, you’re just wasting engine.
The thing to remember with camshaft selection is how the cam will work with your engine’s cylinder heads. We need to take a close look at valve lift with a particular head and determine effect. Some camshafts will actually lose power with a given head because there’s too much lift or duration. This is why we want to understand a cylinder head before choosing a camshaft. You want to seek optimum conditions with any cylinder head/camshaft combination. This means having to do your homework before making a decision.
What type of fuel do you intend to run in your engine? This also affects camshaft selection. We can actually raise compression if we’re running a mild camshaft profile or using a higher octane fuel. It all has to work together. Camshaft timing events must be directly tied to compression ratio. The longer our duration, the lower the cylinder pressure and resulting compression. The shorter the duration, the less air we’re going to bring into the cylinder, which also affects compression. Our objective needs to be the highest compression without detonation, which will harm the engine. With this in mind, we want the most duration possible without compression extremes. Duration is what gives us torque, as long as compression is sufficient.
Valve overlap, as we have stated earlier, is the period between exhaust stroke and intake stroke when both valves are slightly open. This occurs to improve exhaust scavenging. It improves exhaust scavenging by allowing the incoming intake charge to push remaining exhaust gasses out via the closing exhaust valve. Were the exhaust valve completely closed, we wouldn’t get scavenging. The greater the overlap in a street engine, the less torque the engine will make down low where we need it most. This is why we want less valve overlap in a street engine and more in a racing engine, which will make its torque at high RPM. Increased valve overlap works best at high RPM.
Street engines need 10 to 55 degrees of valve overlap to be effective torque powerhouses. When valve overlap starts wandering above 55 degrees, torque on the low end begins to go away. A really hot street engine will need greater than 55 degrees of valve overlap, but not too much greater. To give you an idea of what we’re talking about, racing engines need 70 to 115 degrees of valve overlap. For a street engine, we want valve overlap to maximize torque, which means a conservative approach in the first place. Push overlap as far as you can without compromising torque. We also have to figure in lift and duration with valve overlap to see the complete power picture.
Lobe separation angle is another area of consideration in street cam selection. This camshaft dynamic is chosen based on displacement and how the engine will be used. Rule of thumb is this. Consider lobe separation based on how much displacement and camshaft you’re going to be using. The smaller the valves, the tighter (fewer degrees) lobe separation should be. However, tighter lobe separation does adversely affect idle quality. This is why most camshaft manufacturers spec their cams with wider lobe separations than the custom grinders.
Duration in a street engine is likely the most important dynamic to consider in the selection process. We increase duration whenever less lift is desired. Why? Because we get airflow into the cylinder bore two ways – lift and duration. We can open the valve more and for less time to get airflow. Or we can open the valve less and keep it open longer via duration to get airflow. Each way will have a different effect on performance. Desired duration should be determined by how much cylinder head and displacement you have, and how the engine will be used. Excessive duration hurts low-end torque, which is what we need on the street. So we have to achieve a balance by maximizing duration without a loss in low-end torque. We do this by using the right heads with proper valve sizing. Large valves and ports don’t work well at all for street use. Mix in too much duration and you have a real slug at the traffic light.
So what does this tell us about duration? Plenty. We want greater duration whenever displacement and valve sizing go up. Increasing duration falls directly in line with torque peak and RPM range. And this does not mean we necessarily gain any torque as RPM increases. It means our peak torque simply comes in at a higher RPM range. For example, if our engine is making 350 ft-lbs of torque at 4500 rpm and we increase duration. We may well be making that same amount of torque at 5200 rpm. In short, increased duration does not always mean increased torque.
Compression has a direct effect on what our duration should be. When we’re running greater compression, we have to watch duration closely because it can drive cylinder pressures too high. Sometimes we curb compression and run greater duration depending on how we want to make power. When we have greater duration, our engine is going to make more power on the high end and less on the low end. This is why you must carefully consider duration when ordering a camshaft. Higher compression with a shorter duration helps the engine make torque down low where we need it most in a street engine. The thing to watch for with compression is detonation and overheating. Maximum street compression should be around 10.0:1.
Valve lift is an issue we must think about as it pertains to an engine’s needs. Small blocks generally need more valve lift than big blocks. As we increase lift, generally we increase torque. This is especially important at low and midRPM ranges where it counts on the street. Low-end torque is harder to achieve with a small block because these engines generally sport short strokes and large bores. Your objective needs to be more torque with less RPM if you want your engine to live longer. Revs are what drain the life out of an engine more quickly.
To make good low-end torque with a small block, we need a camshaft that will offer a combination of effective lift and duration. As a rule, we want to run a longer intake duration to make the most of valve lift. We get valve lift via the camshaft to be sure. But, rockerarm ratio is the other half of the equation. The most common rocker arm ratio is 1.6:1, which means the rocker arm will give the valve 1.6 times the lift we have at the cam lobe. When we step up to a 1.7:1 ratio rocker arm, valve lift becomes 1.7 times that which we find at the lobe.
When we’re calculating valvetrain specs, it is best to achieve a balance all around. If you run a high-lift camshaft with a 1.7:1 rocker-arm ratio, you may be getting too much lift, which means excessive wear and tear. It is best to spec on the side of conservatism, especially if you’re building an engine for daily use. Whenever you opt for an aggressive camshaft with a lot of lift, you’re putting more stress on the valvestem, guide, and spring. The constant hammering of daily use with excessive lift is what kills engines without warning.
We will take this excessive wear logic a step further. It is vital that you ascertain proper centering of the rocker arm tip on the valvestem tip when you’re setting up the valve train. We do this by using the correct length pushrod for the application. Buy a pushrod checker at your favorite speed shop if ever you’re in doubt. A pushrod checker is little more than an adjustable pushrod that you can use to determine rocker-arm geometry. If the pushrod is too long, the tip will be under-centered on the valvestem, causing excessive side loads toward the outside of the cylinder head. If the pushrod is too short, the rocker-arm tip will be over-centered, causing excessive side loading toward the inside of the head. In either case, side loads on the valvestem and guide cause excessive wear and early failure. This is why we want the rockerarm tip to be properly centered on the valvestem for smooth operation.
One accessory that will reduce valvestem tip wear and side loading is the roller-tip rocker arm. Roller-tip rocker arms roll smoothly across the valvestem tip, virtually eliminating wear. Stamped steel, roller-tip rocker arms are available at budget prices without the high cost of extruded or forged pieces.
Lift is the maximum amount a valve-lifter-pushrod combo can be raised off the base circle. Lift is measured in thousands of an inch (.000”). Lobe profile determines how quickly this occurs. It can either be smooth or abrupt depending on lobe profile.
Duration is the amount of time the valve is open beginning when the valve unseats. By this, we mean the number of degrees the camshaft will rotate when cam lift begins. Duration typically begins at .004-inch of cam lift or when the lifter begins to ride the ramp coming off the base circle. “Duration at fifty” means duration begins at .050 inches of cam lift. Duration at fifty is the industry standard for determining camshaft lobe duration. When you’re reading camshaft specs, duration at fifty is the spec you will see.
Lobe Separation (also known as lobe centerline) is the distance (in degrees) between the intake lobe peak and the exhaust lobe peak. Lobe separation generally runs between 102 and 114 degrees (camshaft degrees).
Intake Centerline is the position of the camshaft in relation to the crankshaft. For example, an intake centerline of 114 degrees means the intake valve reaches maximum lift at 114 degrees after top dead center (ATDC).
Exhaust Centerline is basically the same thing as intake centerline. It is when the exhaust valve reaches maximum lift before top dead center in degrees (BTDC).
Valve Overlap is the period of time when both the intake and exhaust valve are both open to allow for proper cylinder scavenging. Overlap occurs when the exhaust valve is closing and the piston is reaching top dead center. The intake charge from the opening intake valve pushes the exhaust gasses out. Valve overlap is also known as lobe separation. Camshaft grinders can change lobe separation or valve overlap to modify the performance of a camshaft. Sometimes they do this rather than change lift or duration.
Adjustable Valve Timing is being able to dial in a camshaft by adjusting valve timing at the timing sprocket. By adjusting the valve timing at the sprocket, we can increase or decrease torque. Advance valve timing and you increase torque. Retard valve timing and you lose torque.
You’ve undoubted heard the term “dual-pattern” camshaft. A dual-pattern camshaft runs different profiles on the intake and exhaust side. We tend to run dual-pattern profiles whenever we’re pushing the revs up. Typically, a dualpattern camshaft will run a shorter exhaust valve duration due to less time required to scavenge the exhaust gasses at high RPM. It is also beneficial whenever we’re running nitrous, supercharging, or turbocharging, where exhaust scavenging is rapid and furious. Running a dual-pattern camshaft on the street doesn’t make much sense because we lose torque and fuel economy at low and mid-RPM ranges. Keeping the exhaust valve open longer is what helps a street engine.
If you’re building an engine for racing, it is a different picture than we find with street engines. Camshaft profile in a racing engine depends upon the type of racing you’re going to do, vehicle weight and type, even the type of transmission and rear axle ratio.
Drag racing mandates a different camshaft profile than road or circle track racing. A short track racing engine will need to be able to produce huge amounts of torque in short order, for example. The same is true for a drag racer. These issues teach us something about engine breathing. Breathing effectiveness is determined by camshaft profile.
Lobe separation for the drag racing camshaft should be between 104 and 118 degrees. There is a broad range because drag racing needs can vary quite a bit. This is where you have to custom dial in your application with a camshaft grinder. Most camshaft grinders have computation charts that show the right cam for your application. As your needs change, so must the camshaft profile. If you’re going road racing, lobe separation becomes more specific, probably somewhere in the 106 degree range. Some cam grinders push lobe separation higher for the circle track engine, depending on conditions. Generally, the higher the lobe separation, the broader the torque curve (more torque over a broader RPM range).
Why Degree A Camshaft?
Making power isn’t just about a longer stroke, large-port heads, big carburetor, and a lumpy camshaft. It is also about the science of setting up your engine properly. It is important to know why we degree camshafts after they’re installed inside an engine, and what this accomplishes.
Degreeing a camshaft is like a Columbo investigation. Call it, “just one more thing, Sir…” in your quest to learn the truth about power. The most basic reason for degreeing a camshaft is to determine that you have the correct grind for the job. Camshaft grinders today employ the most advanced technology available. As a result, few faulty camshafts ever make it to the consumer. However, camshafts do get packaged incorrectly at times, which means you could receive a completely different grind than appears on the cam card and packaging. All the more reason to degree the cam going in.
We degree a camshaft by bolting a degree wheel to the crankshaft, cranking the number one piston to top dead center, and installing a timing pointer. You can get a degree wheel from Comp Cams, Crane Cams, Performance Automotive Warehouse, and any number of other performance shops across the country.
We find top dead center with a bolton piston stop that screws into the spark plug hole or at the top of the block with the head removed. We suggest doing this with the cylinder head removed, which provides the greatest accuracy. Begin this process by turning the crankshaft clockwise until #1 piston comes up to top dead center. With the cylinder head installed, hold your thumb over the spark plug hole and listen to the air being forced out by the piston. The air will stop when you reach top dead center.
At this point, both timing marks on the crank and camshaft sprockets should be in alignment at 12 and 6 o’clock. Install the degree wheel next and align the bolt-on timing pointer. With all of this accomplished, the number one piston should be at top dead center, with the degree wheel and pointer at zero degrees. This becomes our base point of reference. Everything from here on out becomes BTDC (before top dead center) or ATDC (after top dead center). The intake valve will open at a given number of degrees after top dead center and close at a given number of degrees before top dead center. The exhaust valve will open at a given number of degrees before top dead center and close a given number of degrees after top dead center. Much of this depends on valve overlap.
Just as the camshaft and valvetrain determine an engine’s personality, so does the induction system. With electronic fuel injection, planning and execution is pretty straightforward because manufacturers have done most of the work for you. Most of it is boiler-plate where components are designed specifically to work together in harmony. Manufacturers walk you right through the process with a package of components that will work well together. You can even fine tune it to work well with your particular application.
For those of you who choose carburetion, your job as an engine performance planner becomes more involved. Because carburetion is decidedly involved just by itself, we’re going to address it first. Carbureted street engines need long intake runners in order to produce good low and mid-range torque. Longer intake runners are found in dualplane intake manifolds like the Edelbrock Performer and Weiand Stealth. Installing an aftermarket manifold like the Performer or Stealth improves performance because it improves airflow velocity into the combustion chambers. This is likely one of the best modifications you can make to a street engine without selling off the farm.
It is easy to be lulled into believing a larger carburetor, more aggressive camshaft, and large-port heads will make more power. But this isn’t always true, especially in budget street engines. Induction, camshaft, and heads should always synch with your performance mission. What’s more, you want your engine to survive while making all that power. Your engine build plan needs to include a common sense approach that involves the right selection and packaging of parts for best results.
If you’re building a driver for the daily commute, you’re going to have to compromise to some degree in terms of performance if you want reliability and some level of fuel economy. We compromise because radical engines don’t do well for the daily drive. They also struggle to pass a smog check, depending on where you live. Radical camshaft profiles give the engine a rough idle, which can be frustrating in traffic and make it virtually impossible to pass a smog check. Loud mufflers can cause hearing damage and make for an annoying drive. They can also get you a ticket for noise pollution in some communities. A high compression ratio can cause overheating when traffic comes to a stop. Over-carburetion fouls spark plugs and pollutes the air.
This brings us to another valid point – air pollution. Environmentalists and performance enthusiasts don’t get along, but it is our responsibility as performance enthusiasts to build and tune our engines for cleaner emissions and better human health. This doesn’t mean you have to go out and buy catalytic converters and a smog pump. It does mean you need to package your induction and ignition systems for optimum emissions performance at the tail pipe. To sum it up, clean up your performance act.
A big 750 or 850cfm carburetor looks good and works well at the drag strip, cruising spot, and car show. However, these are not practical carburetors for everyday street use where clean emissions and some level of fuel efficiency are important. We want carburetor size and engine mission to be compatible for optimum performance and cleaner emissions. If you think this clean emissions issue is a lot of nonsense, consider the last time you were behind a hopped up vintage muscle car or street rod in traffic. The obnoxious exhaust gasses made your eyes water, didn’t they? Think of the other guy and clean up your filthy tailpipe emissions. And consider this, if your vehicle falls under the guidelines of state emission laws and smog checks, the law doesn’t give you a choice. Clean up your exhaust emission or face revocation of your license plates in some states.
Building an environmentally responsible engine doesn’t have to be difficult either. Carbureted engines are not going to burn as clean as their fuelinjected counterparts. If you can run electronic fuel injection, do so for cleaner air. Do so for your own health and for the sake of others who breathe. If you can’t, be conservative in your performance plan and dial in the right size carburetor. Instead of a 750 or 850cfm carburetor, opt for a 600 or 650cfm carb and see how your engine performs. A carburetor that’s too small will quickly become apparent in the absence of torque as RPM increases. Large carburetors give us more torque on the high end. Smaller carburetors do well on the low end. Choosing the right amount of carburetion is often trial and error.
Keep proper carburetor jetting in mind too. Jets that are too large will make the engine run rich or fat, watering the eyes of those who have to follow you. Jets that are too small can be harmful if you’re leaning on it hard and lean detonation burns a hole in a piston. Again, fine tune carburetor and jet sizing for best results. And always err on the side of rich versus lean for longer engine life. If you really want to make a lasting impression on the community, go for a smog check each time you make a carb/jet change and see what it does for emissions. Cleaner air is up to all of us.
Dual-plane, high-rise manifolds don’t always have to be new ones either. Vintage Cobra and Edelbrock dual-plane, high-rise manifolds yield the benefits of low-end torque and high-RPM breathing, and they can be found at swap meets. They do well on the street in stop and go driving, and they yield plenty of power when it’s time to rock. Single-plane intake manifolds like the Edelbrock Torker, Torker II, Tarantula, and even the Streetmaster are not good street manifolds because they’re designed to make torque at 3000 to 7000 rpm. However, we see them on a wide variety of street engines where a good dual-plane manifold would work much better.
Long intake runners and a dualplane design are but two reasons why we can achieve good low and midrange torque from a carbureted engine. We also want cool air both ahead of the carburetor and beneath it. To get cool air before the carburetor, we need to source cool air from outside. Underhood air is much hotter than the ambient air outside. If we can drop the intake air temperature by 50 to 80 degrees F, this will make a considerable difference in thermal expansion inside the combustion chamber. We can net nearly 10 percent more power this way.
We get cooler air with a hood scoop or a ram-air scoop at the leading edge of the vehicle. Ram air can be sourced through the radiator support or beneath the front bumper. Ram-air kits can be sourced from Summit Racing Equipment, Performance Automotive Warehouse (PAW), or your favorite speed shop. The choice is yours.
Getting cool induction air after the carburetor requires closing off the manifold heat passages from the exhaust side of the cylinder head. We do this during intake manifold installation by installing the manifold heat block-off plates included in most intake manifold gasket kits. Manifold heat is needed only when the outside air is really cold. A cold intake manifold does not allow the fuel to atomize as well as it does in a hot manifold, which causes hesitation and stumbling. We curb this problem by adjusting the choke to remain on for a longer period of time. Then, when the engine is warm, we still have a cool manifold that offers us better performance.
A popular myth is that we make more power by removing the air cleaner. The thing is, removing the air cleaner allows dirt and grit inside your engine, which shortens engine life. We want a low restriction air cleaner that will effectively filter out dirt while allowing healthy breathing at the same time. K&N air filters meet the mission effectively, but they don’t come cheap. They can be washed and reused, which actually saves you money long term because K&N claims these filters can last a million miles. What’s more, they outperform the nearest competitor by a wide margin. A K&N air filter is money well spent in terms of performance and longevity. The new K&N filter with a separate filter in the lid improves breathing even more.
One of the biggest mistakes enthusiasts make is over-carburetion. It may surprise you to know engines don’t need as much carburetion as you might think. The formula is simple, and without a lot of complex engine math. Small blocks ranging from 221 to 302ci need no more than 500cfm for street use. The 351W and 351C need from 500 to 600cfm. Big blocks displacing 352 to 390ci need 600 to 650cfm. Larger displacements of 406 to 428ci need from 650 to 750cfm. These numbers may sound modest, but they’re all a healthy street engine needs. We have to laugh whenever we see a mildly modified street 302ci small-block with a 750cfm Holley double-pumper. This is way too much carburetor.
The exception to our carburetion formula is racing applications. When we’re going racing, our engine needs more carburetor if it’s going to make torque. Small-blocks can tolerate 600 to 650cfm in racing applications. Higher displacement applications up to 390ci need 700 to 850 cfm. Beyond 390ci, we need 850 to 1050 cfm. Performance tuning is where we learn how much carburetor we’re going to need. Over-carburetion on a street engine wastes fuel and pollutes the air. Too much fuel can be as bad for an engine as not enough. Too much fuel washes precious lubricating oil off the cylinder walls and fouls spark plugs. Your performance objective should also include being environmentally responsible. Plan and tune for cleaner air, not just power. Performance today is a two-way street – efficiency and power. With efficiency, we get power and clean air.
Through the years, we have seen and used a wide variety of carburetors on Ford V-8s. Although the Holley 1850, 4150, and 4160 are legendary performance carburetors, they don’t enjoy the reliability of the Autolite 4100 – that plain Jane four-throat carburetor Ford installed on a wide variety of V-8s from 1957-1966. The 4100 is very reliable and it offers the same level of performance we’re used to with the Holley. Holley carburetors struggle with bowl leakage and metering block difficulties. Metering block passages tend to clog easily, causing idle and driveability problems. We don’t see these problems with the Autolite 4100. Some Holley carbs perform well for years while others tend to be high maintenance. The 1850, 4150, and 4160 tend to be challenging due to their small metering block passages that can easily become clogged. This is a problematic issue common to Holley carburetors.
For most street engines, we suggest a Holley with vacuum secondaries for a smooth transition into high power. Vacuum secondaries work better in street use because they function only when we need them – at wide-open throttle. Mechanical secondaries make more sense in racing use because they come into play more quickly in a linear fashion.
Our message here for the street buff is simple. Be realistic about how your engine will be used and don’t kid yourself. Most of your driving will be normal stop and go with open highway tossed in for good mix. Weekend drag racing will be the exception, not the rule. Build an engine you can live with on a daily basis, then make tuning changes for weekend fun. You need an intake manifold and carburetor that will give you good acceleration and driveability coupled with clean emissions. Companies like Edelbrock and Weiand have done extensive research to improve the performance of their products including improved emissions. Good dual-plane street manifolds like the Performer and Stealth get the job done nicely.
The Autolite 4100 mentioned earlier, available in sizes ranging from 480 to 600 cfm, is a better street performance carburetor than the Holley from a reliability standpoint. It delivers plenty of power on demand and will go for years without much in the way of service. The only exception to this rule is California with its destructive oxygenated fuels that harm older fuel systems. You can expect failing gaskets, seals, and rubber hoses with the California fuel additive MTB. For California vehicles, we suggest hard lining your fuel system between the fuel pump and carburetor and the use of steel reinforced hoses where necessary to prevent fuel leakage and fires.
When your performance requirements mandate something more aggressive than the Autolite 4100, opt for that weekend Holley racing experience with a simple carb swap when you want to go racing. Holleys and Autolite are easily interchanged in an afternoon, which enables you to live peacefully with both. Where carbureted induction systems become tricky is late-model 5.0L High Output V-8 engines because we must build an engine that will pass both a visual and tailpipe emissions smog check. Although you might be tempted to dig your heels in on this one, your goal should always be cleaner emissions for the daily driver.
Choosing A Casting
Choosing a block or cylinder-head casting is a matter of knowing what to look for. Seasoned engine builders we know have certain castings they favor and others they like to stay away from. When it comes to cylinder blocks, the word on the street is simple. Builders like older blocks from 1962 through the mid-1970s. It appears Ford went through a period during the late 1970s into the early 1980s where flawed castings seem to be epidemic. Core shift, cracking, and other irregularities seem to plague Ford castings of the period. But this theory isn’t completely in stone. Each prospective casting needs close inspection before you should proceed further.
Whenever you are shopping for a block casting, also keep bore size in mind. Ascertain bore size before laying down the cash. Despite what a lot of builders will tell you, it is rarely a good idea to bore a small-block Ford beyond .060-inch oversize. Limit your overbore to .040- inch oversize maximum. If you have found a .040-inch oversize block, move on. A .030-inch oversize block can be honed out to .040-inch oversize. Another area of concern is line bore. It is a good idea to check the line bore of any prospective block casting. This isn’t always possible. It is a good idea to get a guarantee with any casting you buy. Make sure you have the option of returning a flawed casting if it is proven irregular or damaged beyond repair. Irregular line bores can be bored and/or honed to take out the irregular alignment.
While you’re at it, make sure the block deck has never been milled. This can be accomplished by sonic-checking, which tells you the thickness of the deck. Thin decks should be passed up. You need room for minor mill work if the deck is warped. And if you’re going to blow squeeze or supercharge your stroker, there must be room at the deck for o-ring grooves.
When we think of the camshaft and valvetrain as our engine’s frontal lobe, it becomes easier to understand how an engine’s personality is formed. Nothing determines an engine’s personality more than the camshaft and valvetrain. With this in mind, what will cylinder heads do for an engine’s personality? Cylinder heads have to synch with the engine’s camshaft profile. It all has to be a cohesive, working package. There is little point in fitting your small-block Ford with a radical camshaft if the cylinder heads won’t allow the camshaft to work to its greatest potential. By the same token, why bother with 2.02- inch intake valves if you’re running a mild street camshaft. Camshaft and cylinder head must work shoulder-to-shoulder for best results.
So how do we match up cylinder heads and camshaft? First, what can you afford in the cylinder head department? If you are limited to factory castings, such as 351W cylinder heads, there remains a lot you can do. A good port job, coupled with larger valves, makes for a respectable cylinder head. Despite everything you’re going to learn about porting 289/302 heads in this book, you’re going to find the 1969-71 351W head with a 60cc chamber is the best factory casting for a 289/302 build-up. The 351W head offers larger intake and exhaust valves, and larger ports. This is a decision that is easy to make. Probably the greatest challenge will be finding 1969-71 351W head castings.
Another thing to consider in selecting a cylinder head is desired compression ratio. Because you are reading this book, we presume you are considering a stroker. A stroker has compression considerations due to the increased stroke. If you’re going to supercharge or blow nitrous through the engine, compression becomes even a greater issue to be considered carefully. You can adjust compression with proper piston selection, or you can search for the right cylinder head combustion chamber size. As the 1970s progressed, chamber sizes grew larger in stock castings because compression ratios dropped. Chamber sizes generally increased to 69cc and higher to get compression down.
Aftermarket Cylinder Heads
The aftermarket brings us so much in terms of choice today. There has never been a better selection of cylinder heads available in Ford performance history. Ford Racing Performance Parts (FRPP) has done its homework when it comes to availability and choice. Choice ranges from the stockappearing cast iron and aluminum GT-40 head casting all the way up to a Yates-style NASCAR head. Few aftermarket companies are more committed to Ford performance than Edelbrock. Because the Edelbrock family races Fords, their research and development people have spent a lot of flow bench and dyno time developing small-block Ford cylinder heads for virtually every need out there.
Across Los Angeles from Edelbrock is Airflow Research (AFR). Like Edelbrock, AFR has spent a lot of time developing some of the best small-block Ford cylinder heads on the market. In fact, no one offers a broader selection of cylinder heads for small-block Fords than AFR. You can custom dial-in your cylinder head selection by simply visiting AFR’s website and examining its selection of castings. The most basic AFR street head is the 165cc, available in two styles – street emission legal, and street/strip, without the manifold heat passages. The 165 is an easy bolt-on head void of valve clearance issues thanks to its 1.90-inch intake valves. Because chamber sizes range from 58 to 61cc, you can dial in your AFR purchase for your particular application. Older 289 and 302 engines want the smaller 58 chambers. Newer applications like the larger 61cc chamber. The AFR 185cc has larger 2.02- inch intake valves and the same duo of chamber sizes at 58 or 61cc.
The AFR 165cc and 185cc castings are excellent street and strip heads. Castings designed for street and strip don’t have the intake manifold heat passages necessary for good warm-up and cleaner emissions. AFR street heads have the manifold heat passages, which improve cold start performance. When we step up to the AFR 205 and 225cc heads, we’re looking at race heads designed more for high-RPM use and breathing. The 205 and 225cc heads do their best work at high RPM. These heads are also designed more for higher displacements between 331 and 392ci. This means they work quite well on stroked 302 and 351W based engines. Both heads have huge 2.08-inch valves, which can present piston and cylinder clearance issues in some applications.
What can AFR heads do for your small-block? Take a look at the flow bench numbers compiled by AFR. These numbers were observed at 28-inches of water with 1 7/8-inch exhaust pipe.
Ford Casting Identification
Ford makes it easy for enthusiasts to identify corporate castings. Please understand that Ford casting numbers aren’t always the same as part or engineering numbers. Identifying a casting is a matter of knowing what Ford part and casting numbers mean. Here’s what you can expect.
TYPICAL FORD PART/CASTING NUMBER
It’s easy to identify Ford castings once you understand the system because there’s not only a casting number, but a casting date code that tells you exactly when the piece was cast. Not only that, a date code is stamped in the piece, which tells us the date of manufacture. With these two date codes, we know when the piece was cast and when it was ultimately manufactured. Ford part numbers can be found in the Ford Master Parts Catalog on microfilm at your Ford dealer or in one of those obsolete 900-pound parts catalogs from the good old days. Because Ford has made a great many parts for vintage Fords obsolete, these part numbers don’t always exist in present day dealer microfilms. This is called “NR” or “not replaced” which means it is no longer available from Ford. However, casting numbers on parts tell us a lot about the piece
Here’s how a typical Ford part/casting number breaks down.
- First Position indicates Decade (C5AE-6015-A):
B = 1950-59
C = 1960-69
D = 1970-79
E = 1980-89
F = 1990-99
- Second Position indicates Year of Decade (C5AE-6015-A):
- Third Position indicates Car Line
M = Mercury
O = Fairlane & Torino
S = Thunderbird
T = Ford Truck
V = Lincoln
W = Cougar
Z = Mustang
- Fourth Position indicates the Engineering Group (C5AE-6015-A):
A = Chassis Group
B = Body Group
E = Engine Group
If the item is a service part, the fourth position then indicates the applicable division as follows.
Z = Ford Division
Y = Lincoln-Mercury
X = Original Ford Muscle Parts Program
M = Ford Motorsport SVO or Ford-Mexico
- Four Digit Number indicates the Basic
Part Number (C5AE-6015-A): The basic part number tells us what the basic part is. For example, “6015” in the example above is a cylinder block. The number “9510” is carburetors, and so on. Each type of Ford part, right down to brackets and hardware, has a basic part number. This makes finding them easier in the Ford Master Parts Catalog.
- The last character is the Suffix (C5AE- 6015-A):
The suffix indicates the revision under the part number. “A” indicates an original part. “B” indicates first revision, “C” second revision, “D” third revision, and so on. During Ford’s learning curve with emissions in the 1970s, it was not uncommon to see “AA”, “AB” and so on in cylinder head casting suffix.
Date codes can be found two ways in Ford castings. When the four-character date code is cast into the piece, this indicates when the piece was cast at the foundry. When it is stamped, this indicates the date of component manufacture.
5 A 26
Year (5)/Month (A)/Day (26)
TYPICAL DATE CODE
Another area of interest to Ford buffs is where the piece was cast or forged. With Ford engines, we’ve seen three foundry identification marks. A “C” circled around an “F” indicates the Cleveland Iron Foundry. “DIF” indicates Dearborn Iron Foundry. “WF” or “WIF” indicates Windsor Iron Foundry. Single and double digit numbers typically indicate cavity numbers in the mold.
Five Bolt vs. Six Bolt Bell Housing
Although it is unlikely you will stumble across a block with the five-bolt bellhousing pattern, it is easy to get mixed up and buy the wrong block. The 221, 260, and 289 blocks from 1962-1964 all had five-bolt bellhousing patterns. Ford enlarged the bellhousing bolt pattern to six bolts in 1965 to reduce noise, vibration, and harshness. This six-bolt bellhousing pattern has been the standard ever since with 289, 302, 351W, and 351C engines. If you’re building a 1963 Fairlane or 1964 1/2 Mustang with the original transmission, then you want a block with the five-bolt bellhousing pattern. The 221 block will have 3.50-inch bores. The 260 has 3.80-inch bores. The 289 block will have 4.00-inch bores.
Aftermarket Engine Blocks and Sources
How Much Rod?
Undoubtedly, you’ve heard of “longrod” strokers. What are the benefits of a longer connecting rod? Is going with a longer connecting rod worth the cost? Opting for a longer connecting rod does make a difference in power because it improves combustion efficiency. A longer rod improves combustion efficiency by allowing the piston to dwell longer at the top of the cylinder bore. When the piston stays at the top of the bore longer, this allows us to pull more power from the same amount of air and fuel. The longer the connecting rod, the longer the piston is permitted to stay at both the top and bottom of the cylinder bore. This allows us more time to extract energy from the fuel/air charge.
Speed-O-Motive, as one example, offers a variety of long-rod stroker kits designed to make the most of your smallblock power project. Lets use a 351W engine as one example. In box-stock form, the 351W has a 5.956-inch long connecting rod. It has been proven that you can stroke the 351W to as much as 429ci in a factory block. We can fit as much as 6.580- inches of connecting rod into a 351W stroker. This gives us 0.62-inch more rod, not to mention more dwell time.
Internal combustion engines tend to waste approximately 70 percent of the heat energy they create. Allowing the piston to dwell longer at the top of the bore enables us to capture some of the wasted heat energy, which is absorbed by the coolant or lost out the tail pipe.
Dampen the Vibes
Ford used a number of harmonic balancers over the small-block Ford’s production life. From 1962-1969, a three-bolt balancer was used. In that period, there was a narrow balancer for 221, 260, 289- 2V, and 289-4V engines. The 289 High Performance engine received a wide three-bolt balancer, plus a counterweight. In 1968- 1969, the 289 and 302 engines received a wider three-bolt balancer that was marked differently than the narrow 1962-1967 balancer. Beginning in 1970, small-block Fords received a four-bolt balancer that was used well into the early 1980s. With the onset of serpentine belt drive came a new generation of four-bolt balancers for 5.0L and 5.8L engines.
Written by George Reid and Posted with Permission of CarTechBooks