10/21/2019
Early Small block chevy cylinder heads identification and aplication. Over the years GM has made hundreds of different cylinder heads with different casting marks and valve sizes, combustion chabers and poerts for a small block some good some bad, I'm just going to focase on the earlyheads from the first 20 years or so of production.
When Chevrolet released the mighty mouse 265ci in 1955 they had some economy size heads most of the first engines never made more than 200hp. Right around 56 or 57 they released the 283ci version with optional power pack heads casting mark shown in picture #3. The power pack engine options also included dual 4bbl intake and a power pack camshaft originally designed by ed iskiderian, was the first factory engine to produce more than 1hp per cubic inch. The power pack heads stuck around until 1967. Almost all had 64cc combustion chambers and 1.74" int valve and 1.50" exaust valve, the port caricteristics where small and restictive similar to the later ford small block heads that always proved to restrict power.
Jump ahead to 1962 GM finally releases the turbofire 327ci as the new high performance engine along with it a new set of heads the infamous "camel humps", shown as picture #1. The camel hump was a feat in prefomance 64cc combustion chamber and either a 1.94" intake and 1.50" exaust or the moster 2.02" intake and 1.60" exaust that became famous. The "double hump" or "camel hump" heads where designed from the factory with racing in mind. The ports we larger than any other at the time and flowed better than most ported earlier heads producing at its peak 375hp according to the factory on a fuel injected corvette 327, the factory rating where actually under marked for insurance reasons they actually produced more like 400hp. The heads where designed for the new 4inch bore of the 327 but when installed on a 283 the 2 inch valve caused flow problem on the 3.875 bore where the valve was shielded by the cylinder wall. As ive found from personal experience the optimum head for a 283 is a 1.94 intake valve but going over .500 lift is risky otherwise you can cause flow problems.
By 1968 GM had ditched the small jornal forged crank engines and the famous camel humps allong with it. As the rise of a Camaro and other muscle cars hit its peak they needed a head to match the horsepower damands. The new set of heads was a variation of the camel humps, seen in picture #2 the 1968 and 69 heads with the accessory holes, they came with 64cc and 62cc combustion chabers and 1.94 intake 1.50 exaust valves, smaller than the earlier heads but these heads have better port caricteristics and larger exaust ports than the earlier camel humps and also came with hardend valve seats, but the smaller vlaves are normally a killer for pepole when buying heads, the diffrence isnt much but in my opinion they are the optimum head for a 283 because of flow and valve sizing.
In general factory iorn chevy cylinder heads can keep up with some aluminum aftermarket heads sutch as the rare angle plug heads that where built and sold for racing only. But if you know what your liking at you can find a head that is cheap as a stock head that will flow as good as a aftermarket head. Ive always been a fan of building the smaller lesser built engines like the 283, so far ive acheved 450hp at 8500rpm out of a 1967 283cid on gas, with a stock but ballenced bottom end and all vintage period correct parts, I'm looking to make 475 and 9000+ with just a intake manifold change from a torquer 1 manifold to a long runner yunick ram manifold. Its quite a jump but the intake runners where to short and the cam and block have a lot more rpm and power left in it. So don't be discouraged by smaller vintage engines.
