Exactly! I am always amazed when a motor makes good power with a cam with a single pattern. What are the chances of the intake & exhaust needing the same pattern????
[/quote]
Compression ratio has a big effect. A low compression engine ,say 8/1, still has usable cylinder pressure farther down the bore than a. 16/1 motor so the 16/1 motor can get away with a lot more exhuast duration. The decrease in working pressure of the 16/1 motor occurs twice as fast since the volume in the cylinder doubles twice as fast.