351 Cleveland Cylinder Heads Guide: Factory Iron Heads

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.

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This is the D1AE-GA 351C-4V fitted with pushrod guide plates and screw-in ARP rocker arm studs, which are modifications. The 351C-4V head has bolt-fulcrum, stamped-steel, no-adjust rocker arms. The Boss 351 head has screw-in studs and guide plates, and it has the same D1AE-GA casting number meaning both have the same head casting, but are machined differently.

 

The 351C-4V head made the Cleveland famous for huge amounts of high-RPM horsepower and torque. There are two types of North American 351C 4-barrel heads: closed wedge chamber and open chamber. This is the 62- to 63-cc closed-chamber wedge head.

 

The 351C-4V head has huge 2.50×1.75-inch drive-through intake ports designed for high RPM use. Though the 4-barrel head is a factory iron piece installed on production vehicles, it was engineered primarily for racing. The same casting was installed on Boss 302 engines, except for water-passage differences.

 

This is the D0AE/D1AE 351C-4V head with closed 62- to 63-cc wedge chambers and 2.19/1.71-inch valves.

 

The 351C open-chamber head (2V and 4V) is a poor choice regardless of what you intend to do with your Cleveland. People associate this chamber with the smallport, 2-barrel head; however, it is also the 4-barrel head chamber for 1973–1974. This chamber offers zero quench and is prone to detonation. Valve shrouding is fair, but not much consolation when you consider the overall chamber.

 

Cleveland cylinder heads were among the first to have bolt-fulcrum, stamped-steel rocker arms, which had pedestals like this. It is a no-adjust design (hydraulic lifters only); just slowly tighten and torque to spec. The 385-series big-block was the first to have bolt-fulcrums in 1968.

 

The Boss 351 head has screw-in studs and guide plates due to the mechanical lifters; however, this is a modification you can make to any Cleveland head with a good machinist. Bolt-fulcrum pedestals are machined down to make room for guideplates, then drilled and tapped for screw-in studs.

 

Cleveland foundry castings have this CF logo. Though we call these engines “Clevelands,” cylinder heads were also cast at the Windsor, Ontario, foundry and have a “WF” mark.

 

Here’s a “WF” (Windsor) casting on a Boss 302 head, which demonstrates not all Cleveland heads were cast at the Cleveland facility.

 

Casting numbers accurately identify head castings. This is a D0ZE-6090-A Boss 302 head casting with 2.19/1.72-inch valves. It is a closed-chamber Cleveland head casting with cooling passages for the Boss 302 block and induction. Note the milled pedestals and screw-in stud holes.

 

 

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.

 

Based on years of experience, I can tell you “4” means a 4-barrel head with large ports. The dome indicates an open-chamber head. If there’s no dome (indicated by a dot), you’ve found closed-chamber heads.

 

Powerheads can set you up with turnkey CNC-ported Australian Cleveland cylinder heads with the common-sense combination of closed wedge chambers and 2-barrel ports for improved lowto mid-range torque. Once these heads are CNC ported, they get hardened exhaust valve seats and a valve job along with 16 new stainless valves and the right spring pressure for your camshaft. This particular head is an Aussie 302C with even smaller wedge chambers.

 

Port sizing on this 302C Australian head is comparable to the North American 351C-2V head. What you get with the Australian 302C head is smaller, 57- to 59-cc chambers and higher compression. Casting numbers begin with “AR” along with a North American number on the valley side of intake ports. For example, “ARD1AE” on one and “6090A” on the other stands for “AR-D1AE-6090-A.

 

Regardless of what you’re going to do with your iron-head Cleveland, step up to hardened exhaust valve seats for durability with unleaded fuels. Here the iron seat is being cut out in preparation for a steel seat.

 

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.

 

The hardened exhaust valve seat must be driven into place before getting a nice angle cut.

 

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