Any internal combustion engine requires the properly timed and correct amounts of three basic things to function: air, fuel, and spark/ignition. Relative to air, the combination of the camshaft, valvetrain, and cylinder heads have the greatest influence over its potential for flow through the engine. Of course, the intake and exhaust systems play a role as well, but their contribution is secondary (see Chapter 3). All early-production Mustangs came equipped with overhead-valve pushrod engines so this chapter covers upgrades applicable to these engines only.
This Tech Tip is From the Full Book, FORD MUSTANG 1964 1/2 – 1973: HOW TO BUILD & MODIFY. For a comprehensive guide on this entire subject you can visit this link:
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I cannot make specific camshaft/ valvetrain recommendations because of the many variables. I can, however, state that a roller hydraulic camshaft almost certainly is the best option for most of the vehicles covered in this book. In the case of a daily driver, it’s unlikely a new camshaft or most other valvetrain modifications are cost effective.
The streetable track-day car almost always gets a new camshaft along with other valvetrain modifications. The cylinder heads, camshaft, and valvetrain are interdependent so they need to be upgraded as a system; they provide a new level of performance. Most vehicles are first modified by upgrading the more readily accessible, bolt-on components such as the intake, exhaust, carburetor, etc.
When all of this has been done the choice is then between leaving the stock engine alone (other than maybe just installing some higherratio roller rocker arms), installing a power adder (nitrous, supercharger, etc.), or taking the engine apart to replace the cam, valvetrain, and/ or heads. Installing a new combination requires a much higher level of commitment to performance and requires more skill and more knowledge, though not necessarily more cost. You need to determine your budget and performance goals.
You can get similar performance going either route for a similar setup, though some power adders, such as nitrous, are more intermittent in their usability. An “all-engine” solution provides increased performance under all conditions, whenever you want it, but often reaches a point where the engine is too peaky in nature. A mild to moderate performance engine typically relies on bolt-on parts and/or a power adder, with perhaps the only “internal” engine change being the use of higher-ratio roller rocker arms. Once you decide to go beyond moderate performance, power adder or not, you inevitably need to make changes to the internals to safely, reliably, and fully achieve the higher power/ performance levels you’re after.
Flat-tappet camshafts have no place in a modern street/strip/track engine and solid roller camshafts are suitable only for pure race cars. Today’s advanced roller hydraulic cams are the ideal choice for most high-performance street engines. They offer the advantages of roller design and internal hydraulics allow them to self-adjust. You get the best of all worlds. You can run very aggressive camshaft profiles with minimal friction and periodic adjustments are not required.
Modern hydraulic roller camshafts essentially provide racing technology for the street but do so without the need for the continuous maintenance of solid rollers. The latter still have their place with the highest-revving and/or highestoutput engines used mostly in drag racing. Hydraulic roller cams are now generating very high flow rates, power, and performance while remaining totally streetable.
Many hydraulic roller camshafts are available for Ford small- and big-block engines. A wide range of manufacturers offer so many combinations for various applications and setups that it’s impossible to cover all the relevant combinations. I assume you will use a hydraulic roller camshaft because very few vehicles need a solid roller. Simply put, more lift is better as long as the valves don’t contact the pistons. More valve lift is essentially free performance because the engine breathes better with no real consequence in terms of driveability, idle quality, etc.
Older camshafts needed more overlap and duration to provide higher lifts and flow. Advances in roller hydraulic camshaft ramp design make it possible to achieve pretty high lift without the need to also have excessive overlap and duration. In general, you should go for as much lift as you can while still ensuring an adequate margin of clearance so the valves never hit the pistons. This must be verified. Any reputable engine/machine shop knows to check this and a crate engine manufacturer will surely protect against it to prevent returns due to engine damage.
For most street-driven vehicles valve lift in the area of about .550 inch is plenty for some pretty high-power/high-performance levels. The optimum figure, of course, depends on the power level desired, the intended use, the other components being used, and the camshaft timing events (including how it was installed, i.e., advanced, retarded, or straight up). Keep in mind that valve lift (versus cam lobe lift) is affected by the rocker arm ratio used. On an otherwise stock engine going to a higher rocker ratio increases valve lift to improve flow but usually not enough to cause a problem with clearance.
However, it’s best to start with a standard (usually 1.6:1) rocker arm ratio for a new cam. Then, if still more power is desired and it is safely possible to do so, you can easily change to higher-ratio (1.7:1 or so) rockers on the intake and/or exhaust valves to see if that helps. The rocker swap alone doesn’t normally require that you remove the manifold and heads, etc.; just taking off the valve covers should do it. The reduced friction of the roller-style rockers frees up some otherwise wasted energy while also providing longer life due to less wear.
Changing from a 1:1 ratio to a 1.7:1 ratio, for example, increases lift at the valve from .550 to .585 inch, though in some rare cases it may also be necessary to change the pushrod length if the higher lift at the valve causes interference problems between the rocker arm and the valve.
The type of hydraulic roller lifters you use depends on whether you’re using a newer or older OEM block or an aftermarket block. The newer (5.0L, for example) OEM blocks and most aftermarket blocks have provisions to use OEM-style hydraulic roller lifters. If that’s the case, regular OEM lifters (or compatible high-performance/race versions) are used for moderate- to high-power engines. The limitation is usually either RPM or the type of block being used. Stock-type blocks can usually be modified to accept the OEM system. Two holes are drilled and tapped in the valley area to accept the bolts for the lifter retaining plate (the “spider”). This setup works reasonably well up to about 6,500 rpm with a cam of .550 inch or less lift.
If you have a block that doesn’t make provisions for these lifters all is not lost. Crane Cams and others offer retrofit hydraulic roller lifters that look just like the solid roller lifters of old, except they have hydraulic internals. These drop into an older-style block and are even simpler to install than the newer, OEMstyle roller hydraulic setup because these don’t require a spider or “dog bone” lifter guides. They also have precision-fit plunger assemblies and other features that provide increased RPM potential.
Crane’s Retrofit Series, for example, can also be used to replace OEMtype hydraulic rollers for potentially higher RPM because they are more stable at high revs. Sufficiently strong, hardened (to prevent wear from contact with the guideplates), compatible pushrods need to be specified by length after the rest of the valvetrain has been assembled. When only production components are used a standard-length pushrod can be used. However, even when combining components from the same aftermarket manufacturer it is still necessary to determine the correct pushrod length for your particular engine before installing them. This is due to the unpredictable combination of components and tolerances involved plus the need to ensure the rocker arm geometry is correct to avoid interference.
The camshaft and its maximum lift has the greatest affect on choice of springs. To some extent, the mass of all the components between the camshaft and the valve tip also comes into play but this is more of a concern to racers running at extremely high RPM than it is for those with street cars.
The correct springs provide just enough seat pressure and open pressure at maximum lift (using the correct installed height), without any spring bind. Excessive spring pressures not only cause unnecessary stress on the valvetrain components but also hurt performance and increase the likelihood of component failure. You can use a single, dual, or beehive spring but it needs to be suited to the head and the particular engine setup. It’s best to follow the recommendation of the camshaft supplier or, if the springs come with the heads, verify their compatibility.
Assembled cylinder heads typically come with springs and hardware optimized for a particular use in terms of rev range, spring pressures, and so forth. They work well with the majority of camshafts aimed at the same purpose but it’s always best to verify that with the camshaft manufacturer beforehand. There’s no need to use exotic spring hardware unless you’re going to really high revs.
For the vast majority of engines covered here a good-quality steel retainer is fine for a rev range of about 6,500 rpm or less plus they last indefinitely. Lightweight titanium retainers with special valve locks may be required at the super-high RPM of race engines. The same goes for lash caps, spring locators, and stud girdles. Hardened-steel spring cups should, however, always be used on aluminum heads to prevent the springs from wearing away the surfaces they rest on.
The basic choice for valvestem seals is between so-called umbrella seals (usually what’s used in production) and more-sophisticated Teflon/ PC seals (commonly used in racing). Umbrella seals work well for most of these engines as long as they are made from Viton or a similar high-temperature-rated material, which works better than rubber and lasts longer, especially in a higher-output engine. Teflon seals are even more effective at keeping oil away from the valvestem, possibly too much so in street use.
Depending on the type of valveguides, not enough oil may get between the valve and the guide with PC seals, thus potentially causing premature wear. Installing PC seals requires the cylinder heads to be machined around the valveguides so they fit. This is an extra expense that may not be justified on a street performance car, yet it may be more feasible for a streetable track-day car, which sees less street use and where the valveguides can more likely be modified to ensure the appropriate amount of oil reaches them under all conditions. It really comes down to a tradeoff between maximum sealing and maximum valveguide life. Other factors such as spring pressure and maximum RPM also influence the choice.
It’s common practice when upgrading the camshaft and valvetrain to also upgrade the cylinder heads, at least to some degree. By changing the cam, you inevitably need to increase the flow through the heads to get the most benefit from the cam and other upgrades. To achieve optimum performance the engine and its various components need to be treated as a system. All the various parts are matched to achieve the best balance of performance, driveability, and durability. This aspect is neglected far too often by those who just throw parts together without evaluating their compatibility. It’s almost always a question of balance between the desired outcome and the characteristics of the components. On the high end of the power and RPM scale things can surely get a lot more extreme than I address here.
You must ensure the head gasket bore size is correct (especially on a stroker engine) and that the gasket thickness is what you want in terms of durability and compression ratio. Standard “blue” composite, Teflon-coated gaskets are fine for most naturally aspirated engines. When power and RPM become very high and/or a power adder is entered into the mix, it’s best to step up to a multi-layer steel (MLS) gasket set (such as those from Cometic). MLS gaskets don’t require grooves to be machined into the head’s deck surface but they do have certain requirements for the surface finish of the block and the heads.
To better utilize the superior sealing qualities created by MLS gaskets and the thicker deck surfaces of AFR, Dart, and other aftermarket heads it’s also best to use ARP head studs instead of bolts. They’re made from a vastly superior steel alloy that’s much stronger and stretches much less even when the highest cylinder pressures are encountered. Studs are also inherently superior to bolts because they help distribute the clamping load more evenly over the deck surface and within the block, and this greatly reduces head gasket failures.
A bolt twists and stretches as it’s installed, which can lead to lessaccurate torque readings. A stud only stretches as the nut is tightened so the torque reading is more accurate. This improves durability and sealing plus it also helps reduce the distortion of the cylinder walls. That improves sealing and performance while also reducing oil consumption. The proper lubrication and torque figures must still be used but studs are just better at clamping things together. They also can speed up engine rebuilds at the track.
To top off your new heads you want to use a stronger cast-aluminum valve cover set and silicon-metal gaskets instead of the stamped-steel and cork OEM-style components. The cast covers not only look much better but they are more rigid to reduce the chance of leaks.
The perfect complement to cast covers is composite gaskets, which have a metal core covered with silicon gasket material. The metal cores usually have built-in stops to prevent overtightening of the fasteners while the silicon is usually molded with robust knife-edged sealing surfaces, which can be used over and over because no gasket sealant is needed. The covers also come off very easily.
For engines with a 5.0L EFI-style intake manifold that extends over the head a lower-profile valve cover is generally needed for manifold clearance. Check internal clearance to the cover too.
Written by Frank Bohanan and Posted with Permission of CarTechBooks