Midpipes for headers

[1bluemcm]

Hi all. I have an 07 M coupe, in the US so US spec. I have a set of headers, I believe them to be euro headers for Z4M. Kind of forgot I had them, had purchased them probably 10+ years ago and squirreled them away. I understand the main issue for installing these on a NA M coupe is dealing with the mid pipe and the O2 sensors.

I know there are a few options out there available. As I look into this more now, and I don't think I've missed this but possible, I'm wondering why no one has tried to get a midpipe made with cats toward the front, where it makes the most sense being closer to the headers, and resonators toward the rear before the x-pipe? Does anyone know of someone doing this before?

Since this would be custom work, at least for the first set, seems like there would be enough room for a pair of compact, high flow cats, maybe with one slight forward of the other but forward and closer to the headers, and certainly plenty of room for various resonators towards the rear of the mid pipe.

Thought I'd ask. I'd love to put the headers on my M coupe, but I can't do this without working to tune the sound a bit. I know what they are like without the cats on the headers and a straight mid pipe, too much rasp and pretty stinkin loud. I want to keep the exhaust sound really nice, ideally make it even better with the catless headers than it is as OE. I know I could get away with no cats at all, I don't want to do that. I think having at least some high flow cats in there will help with the overall exhaust sound, and I think some sort of resonator will almost be necessary.

Thanks for any help or ideas. Great forum, glad to see it's pretty active for the E85/6.

[Ed Doe]

Bit confused about what you're asking here, but I think the question is 'when I put euro headers on should I modify the standard mid section to move the cats, and has anyone done this before?'

I think the answer to the second part - is cost, and the fact there's no need. I'm not sure what the US spec midpipe looks like but the euro midpipe has a single cat on each pipe toward the rear of the midsection, just before the X-pipe Flanges. I know of at least one owner on here who has a carbon airbox, Schrick cams and standard cats with euro headers and just aftermarket xpipe and back boxes, who made over 380 bhp, so I don't think there's any real restrictions in the stock cats, and therefore no huge need to look at aftermarket cats or decats truth be told, particularly factoring in the cost.

For info, here's a shot of the underside of a car (not mine) with decats; you can see there's actually very little room to move the cats up or down the midsection in any case, it's all quite tight in the oe location, and the available space in the transmission tunnel reduces the further forward you go.

IMG-20230720-WA0003.jpg (217.97 KiB) Viewed 247 times

So I think the answer to the first part of the question (should I modify the midsection) is probably don't bother, just whack the euro headers on with the oe cats/midpipe and you should find the noise spot on (it'll basically be UK/euro spec at that point)

[1bluemcm]

That's a good point, it'll be pretty much what the euro/UK sec is and I can't imagine all those cars running around sounding awful.

I do have a set of Arqray cans/mufflers on it, they've been on for a long while. As I recall, they were a little louder that OE, but surprisingly not too much, and no drone or rasp from them. Improved sound quality quite a bit over the OE cans.

Thanks for the photo. I'm well aware of the layout, have spent a lot of time under the car. All that had to come out when I installed the autosolutions shifter. Best upgrade yet by the way. I just don't want it to get raspy or too too loud. You wouldn't think pulling cats out of the system way up by the front would induce a lot of rasp or a huge increase in noise, but I've been told this can be the result. Which is why I'd consider a mid section retaining cats to keep the ECU happy and resonators to tune the sound more. I probably need to try to find more sound clips of Z4Ms with headers and the rest stock to get a better idea of what I may be in for. Thank you!

[Ed Doe]

No worries. My setup is oe euro headers, 100 cell rsce cats and oe x-pipe and rear boxes, It's so quiet, passes trackday noise limits everywhere! Not really raspy either, despite having half the cells of the oe cats...

[1bluemcm]

No worries. My setup is oe euro headers, 100 cell rsce cats and oe x-pipe and rear boxes, It's so quiet, passes trackday noise limits everywhere! Not really raspy either, despite having half the cells of the oe cats...

That is good to know, thanks for the detail! So maybe with the OE section 1 with the OE cats, OE x-pipe and my Arqray mufflers it would be descent with the euro headers. I guess to put it back is just labor. I'll have to get someone to weld in some O2 bungs on my section 2 after the cats and a EGR bung. But those could be easily capped off.