The Stovebolt Site Forums The Shop Area Engine Shop Which head is best?

I have long wondered why GM designed the combustion chambers as they did. Performance wise and economy wise it's not the strong point of the engine. Was it that the science was not well developed? By the 30s there were both hemispherical and wedge designs on aircraft and racing engines. Was it cost? How does the sort of bath tub design end up cheaper? Was it an accommodation to low octane or poor volatility gasoline? A look at engine designs shown in my old Thomson Products manual shows that GM was the only user of OHV designs on American cars in the thirties and GMC, Mack and Cummins the only truck engines. One can see why Wayne came up with a 12-port head for Chevrolet in the fifties. Too bad GM didn't buy that design from them. The engine still had a 10 lifespan at that time. Anyone know if the Wayne head was a wedge design?

I also note that GMC 228 & 248 engines in the mid thirties had very radical cams -- like over 300 degrees duration. What was that about? Maybe an attempt to limit cylinder pressures at low RPM to prevent detonation? I doubt the engines were ever called on to run over 4,000RPM or so. By the late thirties they were back to more conventional valve timing. All the while compression ratios were like 6.75:1.