[_k_b_k_]

Hi everyone!

Just took ownership of my 19 Z4 M40i. This is my first BMW, first roadster, first 6 cyl and also first modern car too. Loving it so far, but I found the noise it makes to be a bit muted even in sport plus. Also, I bought the car with the intention of getting it tuned (stg2), as I knew as nimble as it is, the stock ~330 hp is not gonna be enough

So yeah, I have an EU model, supposedly with the OPF fitted, although I haven't put the car on a lift yet, will confirm. I read in a couple places online, that the OPF does kill some of the exhaust note, is that true?

And my main question is...as I'm a bit confused on the various parts/components of the exhaust system...so for stg2(+) I'd need decat or sports catted downpipe, and so could I also delete the OPF (I know I'll need to address that in the ECU accordingly too)? Is there anything else between the DP and the OPF section, or is that how it comes together (DP -> mid section with OPF -> axleback section)? And also, can I fit the replacement pipes I've found (Manhart for example) without cutting and welding, or is that absolutely necessary (would like to be able to restore oem state for MOT if possible)

Any help is greatly appreciated. Cheers!

[t0pless]

Euro models were fitted with OPF. This is a reason for less power output and less exhaust sound. Whether you’re doing a custom tune or OTS, you’ll be able to deselect this if you decide to delete OPF.

I’m not familiar with OPF since I’m in the US. Surely this affects emissions readiness, but this is beyond my expertise.

The performance gap between catless and catted are virtually zero with a stock turbo. As you start to get to the 600+whp, the catted downpipe will start to become a bottleneck. At that point, you’re already doing port injection/DI injector upgrades, big hybrid turbo/full frame, and a built transmission or at least torque reduction tuning.

Big reason for me to go catted was to be emissions compliant (GESI is an EPA certification that’s recognized in all states minus California), and also you won’t have the smell of fuel.

DP—> resonator—> axelback. OPF would be somewhere after the DP I believe.

All axleback exhausts will require cutting since there is no flange. An exhaust for these cars are also not a bottleneck until well over 600HP, so modification is strictly for sound. Nearly all aftermarket axle backs will come with exhaust clamps. Installation is best on a lift than stands as the oem exhaust is heavy as hell. Yes, your OPF does affect your exhaust noise.