I read a test where s dude with a big inch Hemi powered street based car had dual 3.5" out of his collectors to a pair of under-the-seat mufflers then into 3.5" tailpipes and he hated the volume of the exhaust.

So he dynod it on the chassis dyno to get a baseline.

He then proceeded to go from 3" to 2.5" to 2" tailpipes out to the rear bum;per and recorded the differences in HP/TQ.

The end result was a loss of a total of 6 HP from the 3.5" tailpipes to the 2" tailpipes yet the sound was WAY quieter and comfortable for him.

Make of it what ya'all will