[clairvoyant]

What is the most restrictive point from an exhaust system (downpipes, catbacks, midpipes, etc) on 335i?
Is it the catalytic converter or the shape/bent of the exhaust system itself?
Thank You

[RoundelM3]

Pipe diameter would be no. 1, with catalysts/mufflers and any bends that reduce the pipe diameter following after. Catalysts aren't all that restrictive, but they are Federally mandated, and in some states, like Texas, it's a huge fine if you remove them from a licensed street vehicle. Doesn't apply to vehicles that aren't street-driven, though.

A "catback" refers to an aftermarket exhaust system that bolts directly to the catalytic converter(s) and goes all the way back to the exit point. Most of these feature larger diameter pipes and high-flow resonators and mufflers. The other option is usually just free-flow mufflers that attach at the same point as the stock mufflers.