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

I've wondered why they dropped down from 2.25" on integrated head cars and 292 SD trucks exhaust, and from 2.5" on the HD 292 and integrated 250 trucks, down to a 2" single tailpipe? The V8 cars had dual 2" tailpipes out of the muffler, but in the L6s they kept a single 2" tailpipe. Seems restrictive.