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.
This Tech Tip is From the Full Book, HOW TO REBUILD THE SMALL-BLOCK FORD. For a comprehensive guide on this entire subject you can visit this link:
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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. Positivestop 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.
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.
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 bigblocks. Instead of the ball-stud rocker-arm setup the small-block Ford had always had, the 1978 and later head has the boltfulcrum, 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 cylinderhead 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 fullblown 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.
We get more power from our smallblock 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.
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 cylinderhead 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 aboutheader and exhaust system compatibility.
Written by George Reid and Republished with Permission of CarTech Inc
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