Inliners International Forums General Discussion Engines Exhaust size effect - is bigger always better?

bcowanwheels says:
"airplanes are hi-compression and run very hi octane fuel plus there tuned to run with exhaust that way. there like a race engine with open headers."
Then Mean buzzen half dozen A.K.A. Hank says:
"Airplane engines in general are low compression air-cooled engines."
Now it is obvious even to my limited intellect, that you cannot both be right.
I am more confused than ever. Perhaps it is time for me to give Google a workout and see what HE says.

regards,Rod.