Turbo Pro Muffler - Optimal Flow, No Drone, No Resonance

Lelo Dart said
Do these mufflers neck down inside the case or are they true to the inlet/outlet pipe size? Looks smaller inside just looking at the cutaway picture.

Don't forget that the muffler nipples are 2.5" OD so that 2.5" pipe can slide into them. The pipe inside the muffler is 2.5" ID. Hope that clarifies.