OK, I'll try to keep the background writing brief.
[pic added later for clarification]
I asked my mechanic friend if he'd install a smaller muffler in a different location, to enable me to do a better job covering the underside for aero improvement. The OEM muffler sits behind/above the rear bumper and I'd like to relocate a smaller muffler over on the side instead.
He says that the only muffler one could find that would fit would be a "performance" fart can. And that the reduced backpressure would fool the fuel management system into messing up the mixture which would defeat my purpose.
My '89 Volvo uses a Bosch Air Mass Meter between the airbox and throttle body, and an oxy sensor located in the cat converter.
He's basing his judgment partially on his own experience in his '85 Volvo that's turbo'd and has significant performance mods on top of that. When he opened up the exhaust system he had to remap his fuel management system. Both of us have 2.3 liter engines, his is turbo and has a mechanical air flow meter vs. my amm. My exhaust is 2" piping + cat + resonator + muffler. His is 3" piping plus cat + 3" exhaust pipe. No muffler.
What do you guys say? Should I go ahead and ask him to do it anyway? Or hunt for a restrictive fart can or add restriction to typical one?