Just thinking out loud but on an N/A,

Dual headers, leading to dual presilencer then into dual muffler like the racing beat ones that have 2" diameter all the way through. So 4inches of exhaust outlet yes? if you combine the 2 pipes

Why when people fit 2 into 1 headers with a 3" outlet to a 3" presilencer then into any 3" rear muffler onto an N/A do you loose power due to lack of back pressure

if you see what i mean

 

i think it has a little to do with lower exhaust velocity in the three inch pipe and three inch inlet/outlet mufflers have very low back pressure compared to the racing beat unit. I could be way out in left field on this, but those are my thoughts.

 

couple things.

one 3" pipe has more area than 2x2" pipes (do the math)

two when you collect the exhaust, it can use the pulses from the other rotor to scavenge the chambers. do a search for scavenging, or rotarygod most likely has a writeup on this.

three backpressue is bad on a rotary, all the time!

 

2 inch or 2 1/4 from block to back near the diff, then into a single 3 inch over the diff and a muffler, you will have to add resonaters and mufflers before the diff if street driven, which will kill flow a bit