[scottj]

Simply stated, engines are basically air pumps. The more air you can pump thru the engine, the more power it will make. The heads determine how much air you can flow through the engine and therefore how much power the engine can make.

Cubic inches dictate how many rpm you have to turn the engine to flow that amount of air.

To make the same power, a 302/331/347 will have to turn alot more rpm than a 408/418/434.

The more rpm you turn the engine the shorter its life, especially valve spring and lifter life.

Also, the higher you turn the engine the more cam duration you need, the earlier you open the exhaust, and the more you will hear the combustion in the headers at idle. That combustion in the headers is what gives it that "pop" or "nasty" sound.
Scott