Although there’s some confusion over Cleveland cylinder heads, the 335-series engine family has the easiest line-up of Ford cylinder heads to understand. • 351C-4V closed wedge chamber (bolt-fulcrum rockers)
- 351C-4V closed wedge chamber, boss/high-output head (adjustable rockers with screw-in studs)
- 351c-2v open chamber (bolt-fulcrum)
- 351C-4V open chamber (bolt-fulcrum)
- 351C Australian head (2v ports with closed wedge chamber)
- 302C Australian head (smaller, closed wedge chamber)
Although this may seem an oversimplification, lacking specifics such as casting numbers and markings, this is what you can expect to find out there at swap meets and online auctions. Which heads should you pursue and which ones should you avoid? Open-chamber, Cleveland 2-barrel and 4-barrel heads, even if your Ford was originally equipped with them, should be avoided. Throw them on the shelf or into the recycle bin because they are terrible cylinder heads.
This Tech Tip is From the Full Book, FORD 351 CLEVELAND ENGINES: HOW TO BUILD FOR MAX PERFORMANCE. For a comprehensive guide on this entire subject you can visit this link:
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Poor quench and chamber irregularities that cause spark knock make the two open-chamber heads unacceptable for a high-performance Cleveland. They spark knock when you start the engine and they knock under hard acceleration, which makes them a poor choice for any Cleveland engine including the 351M and 400 engines. There’s little or nothing you can do with these heads to gain performance or prevent spark knock. I’m puzzled every time I see these heads used for a magazine or buddy’s project because they are such a poor cylinder head. Considering the great wealth of aftermarket and Aussie iron heads available for the Cleveland, there is no reason to ever use an open-chamber head.
There are suitable factory iron Cleveland heads you can use with great success if you know how to work them and know how you’re going to use them. The North American 351C-4V head with closed wedge chambers offers one of the best combustion chambers of its time. However, it is a medium- to high-RPM cylinder head with huge intake ports and lackluster exhaust ports with an ugly floor. It falls on its face as a street cylinder head because there’s insufficient lowto mid-range torque because you’re not going to get velocity at low RPM. Compression ratio is high, which means you need to lower compression via piston dimensions if running pump gas.
The best factory iron cylinder head comes from Ford Australia, which has the optimum combination of North American 4-barrel, closed wedge chambers and 2-barrel ports. This means great quench, good compression, and improved low- to mid-range torque. Torque (and velocity) comes from smaller ports, which is what you want on the street.
Powerheads Performance Engineering takes the great Aussie Cleveland head and does a nice CNC port job along with hand-finish work to set you up with deep-breathing cylinder heads you’re going to like for street and weekend racing. The beauty of the Aussie iron heads from Powerheads is a broad torque curve: 2,500 to 5,500 rpm. At high RPM (5,500 to 6,500), these heads deliver. Of course it all depends on your combination of cam profile, induction, and stroke. This is why you need to know how you’re going to use your Cleveland most of the time. Street drivers operate most of the time in the idle to 5,000-rpm range, which makes the Powerheads a great casting for the daily commute.
You can get into these Aussie heads from Powerheads for around $1,200 a pair. If you desire CNC port work add another $500. CNC port work depends, once again, on how you intend to use your Cleveland. If you’re building a weekend drag racer that’s driven during the week to work, CNC port work makes sense. If it is never raced, don’t waste your money on port work.
If you plan on stroking your Cleveland to 393 or 408 ci, the Aussie Cleveland head becomes debatable depending on how you intend to use it. With a longer stroke comes the need for more breathability. North American 351C-4V heads with their large intake ports work better with displacement in excess of 400 ci. Large ports cultivate the velocity needed with the deep draw of a long stroke, which gives you torque at lower RPM ranges.
Written by George Reid and Republished with Permission of CarTech Inc