How to Choose Heads for Your Small-Block Ford Rebuild

Outside of the five-to-six-bolt bellhousing pattern change for 1965, the next most significant change for the small-block Ford is valvetrain and valve covers in 1966. On May 8, 1966, Ford went to a rail-style rocker arm on the small-block Ford. Instead of a pushrod guide hole cast into the cylinder head, the rail-style rocker arm sat on a taller valvestem, which kept the rocker centered on the valve. At first thought, this is a good idea. But, when you consider engine wear and the possibility of using a high-performance camshaft, this idea is a bad one. As the valvestem tip wears, the side rails get closer and closer to the retainer. Eventually, they work their way into the retainer, which can fail, drop the valve, and destroy the 289/302 blocks were virtually the same except for the cast-in front accessory drive mount on the right-hand side, which first appeared with the introduction of serpentine belt drive. Another significant change was the one-piece rear main seal, which first appeared for 1985. Crankshafts are not interchangeable at this point. Crankshafts with the lip for a two-piece seal will not work in the one-piece seal block. By the same token, the lipless one-piece seal crank will not work in a two-piece seal block because it will leak. The lip works hand in hand with the two-piece seal. Without the lip, it’s a leaker.

 

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Two types of small-block castings had wider main bearing caps – the 289 High-Performance block and all Mexicanblock 289s and 302s. Contrary to what we have all been told through the years, it turns out Mexican blocks are not made of high-nickel iron. They weigh virtually the same as their U.S. counterparts. The only benefit is the wider main caps we find south of the border. engine. Throw in a high-performance, high-lift camshaft, and engine failure becomes probable. Whenever you’re shopping cylinder heads for a 289/302-ci engine, you will want early 289 castings with the pushrod guides cast into the cylinder head. This means using a cylinder head casting prior to April/May of 1966. Look for the pushrod guide holes in the head. From

May 1966 and up, the pushrod hole is round and completely clears the pushrod. If you have no choice but to use heads designed for rail-style rocker arms, opt for pushrod guide plates with screw-in rocker-arm studs. If your budget doesn’t permit this, find a set of 1962 to early 1966 castings.

Another cylinder head engineering change came in 1968 – the positive-stop rocker-arm stud, used in conjunction with the rail-style rocker arm. Positive stop rocker arm studs are a “tighten it up and forget it” type. They are not adjustable.

Other considerations when choosing small-block Ford heads are combustion chamber size, port size, and valve size. When it comes to the 289- and 302-ci engines, port sizes never changed, nor did valve size. Contrary to all of the bench racing you’ve heard through the years, the 289 High-Performance cylinder head does not have larger valves and ports. Combustion chamber size isn’t any different from the 2V and 4V head either. If you desire a smaller chamber and greater compression, opt for the 1968 302-4V head with the smaller 53-cc chamber. It’s the only small-block Ford head that had a smaller chamber. The only exception to this statement is the 1962 to ’64 221- and 260-ci heads, which had smaller 45- to 51-cc chambers. They also had smaller ports and valve sizes, which makes them a poor choice if you’re interested in power. The 1968 302-4V head is a good factory cylinder head if you’re interested in improved low-end torque with a basically stock 289/302-ci engine. However, it is a very difficult cylinder head to find because it was cast for one year only.

Important!

 

Here are the two types of rocker arms used on small-block Fords prior to 1978. On the left is the 1962 through early 1966 rocker arm used on cylinder heads with the pushrod guide cast into the head. On the right is the rail-style rocker arm used from May 8, 1966, through 1977. The rail-style rocker arm, as its name implies, has rails around the valvestem, which keeps the rocker arm centered on the valvestem. This idea saved Ford lots of money in machining costs and simplified design. However, do not use this rocker arm configuration with a high-performance camshaft.

 

Small-block Ford cylinder heads began to change significantly in the 1970s, which is where you need to pay even closer attention to casting differences. Port and valve sizes remain virtually the same for 289/302 heads through the years, but combustion chamber changes a lot after 1971. You guessed it – the chamber sizes got larger. When combustion chamber size increases, compression drops. Ford, as well as all of the U.S. automakers, dropped compression to both improve emissions and deal with steadily falling octane ratings at the time. Beginning in 1975, Ford went with hardened exhaust valve seats for more reliable performance with low-lead and no-lead fuels.

 

Here is the positive-stop rocker-arm stud, which entered production in 1968. Just crank this one down tight and forget it. This is the bolt-fulcrum rocker-arm design that entered small-block production in 1978. It is a no-adjust rocker arm designed only for use with mild camshafts and hydraulic lifters. This design first entered production on the 351 Cleveland middle-block and 429/460-ci big-blocks. It took a decade for it to find use on the small-block Ford.

 

Another point to remember with conventional versus rail-style rocker arms is valvestem tip length. Rail-style rocker arms have a longer valvestem tip than conventional rocker arms. It is a good idea to use the short stem with conventional rocker arms and the long tip with rail-style. Never use the rail-style rocker arm with the short-stem valves.

 

This is the bolt-fulcrum rocker-arm design that entered small-block production in 1978. It is a no-adjust rocker arm designed only for use with mild camshafts and hydraulic lifters. This design first entered production on the 351 Cleveland middle-block and 429/460-ci big-blocks. It took a decade for it to find use on the small-block Ford.

 

This is typical of an early small-block Ford head with smaller 53–57-cc chambers. The very early 221/260 head has even smaller chambers.

 

Here’s a larger 64-cc chamber in an aluminum aftermarket cylinder head. Chamber size affects compression ratio. Aluminum enables you to run more compression because it gets rid of heat more quickly.

 

This is a 351C-4V wedge chamber, which yields an 11.0:1 compression stock. The 351C-2V chamber is an “open” chamber designed to yield less compression. However, the 2V head is more prone to detonation. It’s a tough head to recommend. The 4V head is less prone to detonation, but its huge ports make it impractical for street use.

 

The 351C-4V head offers much larger intake and exhaust ports, but it doesn’t do anything for the low-end torque you need on the street. This cylinder head is happiest at 7,000 rpm. Consider the Australian 351C head, which is a nice combination of conservative 2V port sizing and the 351C-4V wedge chamber. It is the perfect street head for any 351C project.

 

When you are building a small-block Ford with flat-top pistons, you can cheat a little on chamber size, but when chamber size grows to 64cc and beyond, your engine will suffer significant losses in compression – and power. With a 53- to 57-cc chamber and a flat-top piston, you can expect a compression ratio of about 10.5:1 depending on compression height. This is where you really have to do your homework in the planning process. You don’t want to discover you have too much compression, or too little, when the engine is assembled. Check out the Engine Math chapter information on how to precisely calculate your compression ratio.

Beginning in 1978, the small-block Ford cylinder head took on the same rocker-arm set-up as the 351C, 351M, 400M, and the 385-series 429/460-ci big-blocks. Instead of the ball-stud rocker-arm setup the small-block Ford had always had, the 1978 and later head has the bolt fulcrum, stamped-steel, non-adjustable rocker arm. As in 1968, just tighten it up and forget it. This approach works well with stock applications. It does not work well with aggressive aftermarket camshafts, which will tend to beat the stock rockers to pieces. Aggressive aftermarket camshafts call for screw-in studs and adjustable rocker arms. This is a modification your machine shop can handle.

Small-Block Cylinder-Head Identification
Here’s a helpful chart that I put together to help you identify and locate all kinds of Ford factory cylinder heads.

 

Another path to power is cylinder head porting. Head porting is an art that takes years of practice and experience to refine. Our friend, John Da Luz of JMC Motorsports, understands how to make the most of a cylinder head. He has experimented with dozens of Ford cylinder head castings over the years. The result is 289/302 head castings that flow well in excess of 200 cfm on the intake side, which is on a par with some of the aftermarket heads out there. A set of these heads will wake up your low-displacement small-block.

John tells us it’s a matter of understanding port dynamics. Small-block Fords, for example, suffer not so much from small intake ports, but small exhaust ports that do not scavenge well. John’s porting technique removes the thermactor “hump” (all small-block Ford heads have them, even 49-state heads), opens up the port, and smooths out exhaust flow into the header. This port/gasket match-porting job is economical and will yield lots of power. A full-blown porting job and larger valves will give you torque you never dreamed of from a stock head. As a proven engine builder, John can advise you on the best course of action for your small-block Ford.

 

 351W Cylinder Heads

Before the aftermarket really took off, small-block Ford buffs looked to the 351W cylinder head for power improvements. The 351W head gives the 289/302 plenty of breathability with its larger intake and exhaust ports and larger valves. If you port the 351W head, it only gets better. However, if you’re going to go through the expense of port and bowl work on 351W heads, which can run as high as $1,000, you might as well go with good aftermarket aluminum heads instead. Right out of the box, aftermarket aluminum heads outflow and outperform the stock 351W head casting, even with port and bowl work. If you are looking for cheap, bolt-on power, go with 351W heads and leave the ports alone.

The most important issue to remember about 351W heads is which ones were just 302 heads on top of the 351W block. Beginning in the mid 1970s (1975 for truck castings and 1977 for cars), the 351W was fitted with 302 cylinder-head castings – which means port and valve sizes that aren’t any different. Avoid this casting because it won’t make any difference in power. If anything, it will make less power. The best 351W head castings were produced from 1969 to ’74, with right-sized chambers, ports, and valves for the 289/302.

 

Aftermarket Cylinder Heads

If you’re seeking an aggressive camshaft and 400 horsepower, stock cylinder heads probably won’t be your casting of choice. You’re going to want to go with good aftermarket cylinder heads that outflow the stock pieces and weigh less. Any time you’re going to go through the expense of aftermarket cylinder heads, they probably won’t be iron, either.

Aftermarket aluminum heads serve a valuable purpose in so many ways. First, they flow better. Second, they weigh less than iron. Third, they dissipate heat better than iron, which means you can run a higher compression ratio without getting into trouble. These are three very good reasons to go with aftermarket aluminum heads.

 

The Edelbrock Performer RPM cylinder head is a nice upgrade for small-block Fords. For around $1,200, you can improve airflow, raise compression, and boost power with a pair of Performer RPM heads. Aluminum heads conduct and carry heat better than iron heads. They also weigh less. If you are bolting these heads on an older small-block 289 or 302, be mindful of the larger chambers, which will reduce compression dramatically.

 

We get more power from our small-block Ford by increasing the compression ratio. However, with compression come higher combustion temperatures and pressures. Because aluminum is a great conductor of heat, it carries excessive heat away from the combustion chamber. This means we can push our engine a little harder with a higher compression ratio, nitrous, or supercharging.

 

If you happen to be building a stroker, the Edelbrock Victor Jr. is a better head for greater displacements. This is also a good cylinder head for high-revving, low-displacement small-blocks that need generous breathing. Again, remember chamber size and how it affects compression ratio. Check out my factory and aftermarket cylinder head charts for all the info.

 

Holley has struggled to get on the cylinder head bandwagon and be noticed by performance buffs. However, Holley is making strides, and better cylinder heads, these days. These heads are made of 356-T6 aluminum, have “right-sized” intake and exhaust runners, heavy-duty valvesprings and retainers, and are CNC-machined for accuracy.

 

This is the AFR 165 cylinder head – the perfect street head for just about any small-block Ford. If you’re going to raise displacement, the AFR 185, with 2.02/1.60-inch valves may be a better choice. Much depends on piston-to-valve clearance issues. Each of the AFR cylinder heads delivers consistently better performance through its CNC-machined ports and chambers. AFR is a cylinder head company we feel quite comfortable with.

 

Every engine rebuild should include new valves. This helps ensure rebuild integrity by allowing you to begin with fresh valve faces and stems. To save money, you can reface old valves and clean up the valvestems. But, you will never get these surfaces as true as they are new. And remember, most engine failures are caused by some sort of valvetrain mishap.

 

Of all the aftermarket cylinder heads we’ve seen, AFR heads appear to be the best bang for the buck because they flow so well and yield more power. Right in the same ballpark as the AFR head are Trick Flow heads, which do a pretty good job on small-block Fords. The rest of the market, Edelbrock, Ford Racing, and World Products have good cylinder head castings for the money, but few of them perform as well as AFR and Trick Flow on the flow bench and in the dyno room. You need to stay tuned, because the marketplace is ever changing. New cylinder head castings are showing up all the time from these manufacturers. This competition in the cylinder-head market is good news for you, beating a path to your door with better mousetraps all the time.

Guide to Ford Aftermarket Cylinder Heads

If you decide you want to make a little more power than the factory heads can provide, you might be able to find what you need in this chart.

 

 

The main issue to keep in mind with aftermarket cylinder heads is compatibility with existing stuff. More than one of us has purchased aftermarket cylinder heads, only to discover they aren’t compatible with the headers and exhaust systems we already have. This is especially true with raised-port and high-port heads. This is also counterproductive when you’re trying to make power for less money. Cylinder head manufacturers are working harder to improve exhaust system compatibility, but there are still plenty of examples out there in the marketplace that won’t work with your Hooker Super Comps or Shelby Tri-Ys. This is where it gets expensive. When you’re shopping for aftermarket cylinder heads, ask the manufacturer about header and exhaust system compatibility.

Written by George Reid and Republished with Permission of CarTech Inc

 

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