135i exhaust on a 125i/128i with a 1M backbox query

[TwoToaster]

Hello all,

I have bought a complete 135i exhaust for my 125i as it has a hole in from a previous weld job. In future, I would like to put a 1M quad back box onto it, along with a new battery tray and what not.

My question is, should I be worried the exhaust back pressure? I really want quad tips but I want to try and keep things OEM too.

Picture one is my 125i exhaust
Picture two is a 125i exhaust compared to a 135i.

Thanks

[Asianoak]

So I'm not yet a 128i owner (doing my research before buying) but I saw your question and thought I'd respond.

I had a Z4 3.0si with the N52 engine (stock it had the 3 stage intake manifold). A few guys... And I mean very few back then, did a quad exhaust set up on theirs. I wound up pulling the trigger and the sound was awesome. I didn't really notice any power gain... Or loss. But the little burbles and pops was really nice. Not obnoxious either. I was surprised the N52 sounded so good. If I remember correctly I had a muffler shop do a customer "crossover" in order to get the other side.