Exhaust diameter sizing question ZHP & M3

[BH93]

I've been looking at realoem and searching the forums on this... but there's a little back and forth and varying information and wanted confirmation.

Are the ZHP/330i muffler section the same diameter as the section 2 OEM pipes from E46 M3?

In other words, could I chop off the M3 mufflers for my S54 swap with the OEM M3 headers, section 1 + 2, and weld on ZHP mufflers to maintain that stock appearance without backflow issues from diameter shrinking issues?

Real OEM shows the the ZHP mufflers use 50mm (~2") clamps, but some posts show they are 2.25" or 2.5"... I don't have an OEM ZHP exhaust to confirm physically.

Thank you all!

[ZHPizza]

ZHP exhaust is 50mm/2in all the way back. Would definitely choke the larger S54 piping. You could pick up an aftermarket 2.5in catback that would fit perfectly, though. I mean you would still need to weld somewhere along the way but the muffler would fit with the wheel well/diffuser on the ZHP.

[BH93]

ZHP exhaust is 50mm/2in all the way back. Would definitely choke the larger S54 piping. You could pick up an aftermarket 2.5in catback that would fit perfectly, though. I mean you would still need to weld somewhere along the way but the muffler would fit with the wheel well/diffuser on the ZHP.

Yes, I actually saw another thread by George and he already tried multiple variations for his S54 swap and exhaust setup.
Will require cutting length wise after sliding in the smaller muffler and then crimping to get a weld surface between the two pipes, since the S2 pipe is D-shaped as well.

I am planning to maintain the center muffler of the ZHP exhaust as well as the rear and will see how that goes!

[ZHPizza]

I mean you can do it but it's going to hurt your power output. Even if you only use the S54 headers you're still going to neck down from them to the ZHP exhaust and kill the flow velocity.

[BH93]

I mean you can do it but it's going to hurt your power output. Even if you only use the S54 headers you're still going to neck down from them to the ZHP exhaust and kill the flow velocity.

When George did his experiment, there really wasn't a noticeable change (confirmed with DYNO) when he used the ZHP muffler with S1 and S2 of M3 exhaust with the flow shrinkage.

I don't know if I'll see a significant back pressure issue by also including the center muffler considering the stock E46 m3 rear muffler is enormous compared to just the rear muffler of the ZHP

https://www.e46fanatics.com/threads/s54-conversion-muffler-shootout.1266239/page-3#post-18936952

Here's the post for anyone interested

[ZHPizza]

Man that's a great thread. Only a 10hp drop from the 60mm to 50mm inlet mufflers so not bad at all on that scale