[Kinglagos]

Hi, I got a 420i (n20) with an aftermarket catback Bastuck exhaust, Wagner Intercooler and BM3 Stage 1 93. Originally, the 20i has a 60mm diameter exhaust system and the catback I installed has 76mm pipes. As the 20i and 28i share the same cat, the only part remaining as 60mm is the connection pipe between Cat and middle muffler. I have now only these two options that are street legal in Germany:

1) Get the 28i connection pipe part (18307633122) so the system is completely 76mm. Will that help with performance? I could well imagine it is the bottleneck now since I am running close to 28i numbers and that one obviously needs the wider pipes. Costs: ~270€

2) Get a Bastuck Sport Cat (unknown how many cells) and replace both the cat and the connection pipe. Would that allow me to run bm3 stage 2? Cost: ~1500€

Thanks!

[CandyRedRC46]

Are you mixing up the term catback exhaust, with axle back or resonator back etc? A catback exhaust for the F30 should include the front pipe. A catback exhaust should connect to the down pipe, not the front pipe, since the cat is in the downpipe...

[Kinglagos]

You are right, in this regard it's after the front pipe. Cat -> front pipe -> new mid resonator -> end resonator. I decided to switch the pipe to make it "proper" catback.