On a decent-sized engine, 400-inch and up, you start getting close to flat pistons to get 10.5:1. The small engines, like a 300-inch motor, and put a big dome on it, that's not really good for flame travel. As you go larger, you start to revert more to a flat piston, which has the best of the flame travels of all of them. 'The cool thing about big engines is piston design becomes way more practical. If you look at the work being done, if you have to fire the engine 10 degrees earlier on the compression stroke, the engine is now going to have to produce more work because you've started the burn earlier to achieve the same peak ATDC,' he said. On the older, junk cylinder heads, you may have 45 degrees of total timing (approximately a 60-degree time frame). 'And with a good cylinder head, you're looking at a 45-degree time frame (approximately 30 degrees of total timing) from the time you ignite it. Looking at the combustion chamber's efficiency, you can begin to look at compression as a function of the timing advance. He's looking for peak cylinder pressure at 15 degrees after top dead center (ATDC), where the most power is made. The reason for this, Duttweiler explained, is in the time it takes for the flame to propagate during the crankshaft's rotation.

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