JasonS
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BTDT. Won't get much out of a bolt-on deal. Need internal engine mods to enable the increased rpm necessary to get full advantage. Back in the day (based on published dyno results in Bill Fisher's GMC Speed Manual), an all out racing engine with a stock reworked head produced 215 to 236 horsepower; 258 to 285 horsepower with a 12-port head. Hardly seems "tremendous".I have always thought a header would be cool on a gasser deuce (GM 302 engine) and a custom intake you could mount a four barrel carb on. I think I remember there being a lot of aftermarket parts for the GMC. Hummm...goggle is my friend:The 302 GMC inline six was produced from 1952 to 1960 and is a 4" bore and 4" stroke engine. It was used in military 2.5 ton trucks with the HydraMatic transmission, however that engine was a sealed engine for snorkle/submersion use, had an electric fuel pump, and other features such as a deep sump oil pan. From 1952-1959, GMC manufactured the civilian 302 engine which was not sealed, had a mechanical fuel pump, and used a "standard" oil pan. This engine is popular with hotrod enthusiasts because it delivers tremendous power for an inline six engine, is truck built with a heavy cast block, and can take quite a bit of abuse.
If you really want horsepower out a an inline six gas engine, the vortec 4200 is light years ahead even with stock parts.