How best to complete this exhaust

[monovich]

Howdy. Been a minute.

I'm wanting to swap the euro spec exhaust from my Evo II with a USA one at least temporarily. It's time to re-up my tags and The EU one won't pass the sniff test in my state but based on previous experience the USA one will. Last time I did the tags we swapped a USA one and it passed easily but it is back to having the EU exhaust on now.

Previously I had a shop do the work for me but this time I decided to do it myself. I have the stock exhaust off and I have the majority of a stock USA E30 M3 exhaust here but it is missing the back section / muffler.

So my question is how best to complete the exhaust. Should I:

1. Source a brand new USA spec exhaust or at least a used complete exhaust?
2. Have the partial USA spec exhaust that I have completed somehow (with what parts and at what sort of shop?).
3. Other idea?

Interestingly the two exhausts look visually almost identical but I guess the interior catalytic converter components would be different? I was under the impression that the EVO exhaust had fewer or no cats at all?

Also: Since the Evo II exhaust / muffler is super rare does it make any sense to refresh / re-coat it while it is out or does that ruin the originality of it?

ALSO: what do the clamps do right before the muffler box?

ALSO it looks like the USA exhaust was cut, so I'm guessing it would need to be welded to the remaining pipe / muffler? Or is that what those clamps do?

[hardtailer]

Both are stock (Euro and US are identical) catalytic convertors one obviously is no longer converting (perhaps because the ceramic substrate has been knocked out of it?).
Both no longer have the alumised heat shielding around them as shown in the pic below on the right.

Evo2 had no cats but an intermediate silencer pictured on the left in black. This part is identical to and carried-over from the non-cat euro (200hp) M3 to the Evo2.
Only special exhaust part i.e. Evo2-specific is the exhaust manifold as it is a two part design.
Back box is shared with the 195/200hp M3 (perhaps it has polished end tips like the cecotto/ravaglia en Evo3, unsure about that but your picture indicates as such).


Replied below your questions

So my question is how best to complete the exhaust. Should I:

1. Source a brand new USA spec exhaust or at least a used complete exhaust?
2. Have the partial USA spec exhaust that I have completed somehow (with what parts and at what sort of shop?).
3. Other idea?
Get a supersprint center section without cat convertor and connect a stock back box to that.

Interestingly the two exhausts look visually almost identical but I guess the interior catalytic converter components would be different? I was under the impression that the EVO exhaust had fewer or no cats at all?

Also: Since the Evo II exhaust / muffler is super rare does it make any sense to refresh / re-coat it while it is out or does that ruin the originality of it?

No Evo2 exhaust on your pictures so don't bother.

ALSO: what do the clamps do right before the muffler box?

Connect back box to cat convertor

ALSO it looks like the USA exhaust was cut, so I'm guessing it would need to be welded to the remaining pipe / muffler? Or is that what those clamps do?

indeed

[nsubre]

Hi Monovich,
The clamps let you attach the cat to the muffler without welding. That makes it easier to change things. The clamps are originally used on a US 528i which has the same diameter. They replace the swaged clamps that are original on US M3's. And they are stainless so use some antiseize compound when you assemble things. If the cat pipes have been cut short, the clamps might not work well.
Larry

[monovich]

Thanks for the info y'all.

So there *might* be a catalytic converter in both midpipes, but on the one on the right from the UK the converter might be crumbled / gone / not working if it isn't passing smog with it. The one on the left from the USA car may or may not be there and still work, but I'll only know if I disconnect the clamps to the muffler on the UK one, move to the USA one, and re-test the car.

Otherwise the solution might just be:

1. Buy a catalytic midpipe: https://www.bimmerworld.com/Exhaust/...r-Section.html
2. Unbolt the stock muffler box and bolt it to the new midpipe.

Apologies on the newb questions. I'm just doing more wrenching on my car these days.

[M-technik-3]

What I am surprised at is Colorado makes a 30 years old car pass a sniff test. If the fed's give a pass to emissions and safety at 20 years maybe Colorado should as well.