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

Mr Google really didn't answer my question. Perhaps I just couldn't find the info, but I did try. Still would like to know.
Engines like the V12 RR Merlin, Packard,Allison etc all had a little stub exhaust about 3 or 4 inches long. You could see the port inside. They went REAL GOOD.
Surely someone will come up with a detailed answer.

regards,Rod.