That's a long road you've traveled Kenny! :haha: The only thing leftHere are my experience with all sort of combination I have done:
1) 2nd cats/resonator deleted with stock muffler--> sound a little raspier but not much louder than stock. No backpressure loss feeling.
2) 2nd cats/resonator deleted with Meisterschaft GT muffler--> very loud, and loss some backpressure at low-end torque, but feel it pull harder at top-end RPM. Loudest of all combination section1&2&3 from any manufacturers I ever heard on M5.
3) Prime cats/2nd cats/resonator deleted with race muffler--> very loud, and backpressure loss worst than (2). Feel like turbo lag, but pull hard at top-end RPM. The exhaust tone and note were overpower by the raspy sound from the straight pipes (2nd cat/resonator removed)
Finally 4, I went with prime(pre-) cats deleted, stock 2nd cat/resonator with race muffler--> most exhaust tone determine by characteristic of muffler choice with a little groaning/pulsing from headers. No backpressure loss, but top end doesn't feel strong like (3).
I feel like removing section1&2 in some case could overkill the true exhaust note/tone from the muffler itself. If you want to let the true exhaust note come out, keep the midsections stock.
<!-- / message --><!-- edit note --> BTW, with (3) and (4) when removed prime (or pre-) cats, you will have SES light (increase emission)
Sound wise? That would be the most conservation and truely appreciate your exhaust note intended by manufacturer....Could you leave everything stock but put on an aftermarket exhaust (section 3, I think)? What would this do for performance and sound? Those are the two things I really care about. ...
That's a part of the modding journey even it kind of hassle from time to time but it's fun.That's a long road you've traveled Kenny! :haha: The only thing left
to try is high flow cats and perhaps high flow resonator with x-pipe.
Thanks. I should have mentioned that I don't have ecu remapped as yet. That would help a lot on throttle response and tunning to accomodate more airflow from exhaust setup.I gained about 10rwhp and 10rwtq from from adding sections 1, 2 and 3. I didnt notice any of the backpressure loss mentioned above but this could be because I added the ecu at the same time. I did dynos but didnt have any driving time between the mods.