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-   -   m3 stock headers on 325 m54b25 (http://forum.e46fanatics.com/showthread.php?t=955640)

sbcrazy 11-12-2012 07:23 PM

m3 stock headers on 325 m54b25
Hi everyone. So this is what I was thinking. I have a 02 325i. the Cat is going bad (rattling) and I am in need of new ones. I have looked at exhaust options, Headers w/cats, headers w/o cats w/ o2 sims, and oem/ aftermarket manifolds w/cats.

I was wondering if anyone has ever tried using m3 headers w/cats on a non-m car.

I know the flanges don't match the block so you would have to cut the old (325) flanges off and install on (m3) headers. not sure about section 2 alignment from (325)->(m3)

I have been thinking about taking on this project and I'm testing the waters to see if anyone has tried this before. Thanks

p.s. I live in Ca so Smog is a must, otherwise I would run 325 aftermarket Headers.


sbcrazy 11-15-2012 09:12 PM

Really, no input.....


TxZHP04 11-16-2012 08:57 AM

I'm not aware of anyone giving this a try, most just seem to opt for the cheapest headers they can find. Good luck if you decide to go for it.

ThatGuy_JZ 11-28-2012 10:58 AM

From what I've read the E36 shorty style headers will bolt onto the m54b25/b30 blocks, but from there would require some exhaust work to mate the headers to the exhaust, so using an OEM e36 mid pipe for the header connection, then a cut/weld job to the existing E46 piping might work. I thought about pursuing this, then just figured it's a total waste of time and money for only about a 10bhp gain. Not the mention chasing after Check Engine lights and worrying over inspections.

sbcrazy 11-29-2012 05:29 PM

Thanks. Looks like either way I go I'll have some work to do.

SoloII///M 11-30-2012 03:20 PM

O2 sims won't allow you to pass emissions anyway.

sbcrazy 11-30-2012 06:26 PM

If I used o2 Sims I would put cats downstream past the headers. The cats would have quick releases on them so I could put them on for smog and take them off after.

SoloII///M 12-01-2012 08:08 AM

Why would you need O2 sims if you have cats? I'm confused.

If you put a cat in the system you might as well just run O2 sensors and leave the cats / sensors in all the time.

TxZHP04 12-01-2012 09:31 AM


Originally Posted by sbcrazy (Post 14941482)
If I used o2 Sims I would put cats downstream past the headers. The cats would have quick releases on them so I could put them on for smog and take them off after.

Technically this wouldn't be legal either as the cats wouldn't be in the stock location.

sbcrazy 12-01-2012 10:59 AM

O2 sims would be for eBay headers since they do not have cats on them.
And with most BMW cars you can get away with cats downstream because CA SULEV cars have 4 cats. 2 on the manifold and 2 downstream. The smog shop doesn't lift the car up and inspect that here in orange co. You just drive in on rollers.

Still seams like a lot of crap to deal with if I went that route. I'm still leaning on the stock m3 headers with a custom head flange. Cats and o2's would be in stick locations so no cel lights hopefully...

TxZHP04 12-01-2012 11:47 AM

What you can get away with and what is legal are two different things.

SoloII///M 12-01-2012 09:09 PM

But O2 sims don't work. They may make your CEL go away but your DME will still not show a ready flag, meaning you'll fail a smog check.

sbcrazy 08-08-2013 11:00 PM

Ok so the "Frankenheader" project is going to start this weekend. I've got the parts to do it. here are some pics to show how close they are.

sbcrazy 08-08-2013 11:04 PM


sbcrazy 08-08-2013 11:07 PM





taveet330i 08-08-2013 11:32 PM

Re: m3 stock headers on 325 m54b25
Sub'd for results


CrisB02 08-10-2013 10:47 AM

I am very interested on how this will pan out. sub'd

sbcrazy 08-10-2013 10:29 PM

Nope. It did not work. The m3 headers hit the bell housing and the pipes are at the wrong angles. Maybe if I had a shop I would attempt this, but doing it in the street and only 2days with the car before having to use it for work doesnt work. Also the oval pipes on the stock manifold would need a lot of re working. But an idea would be to use s50 headers. Those have the right manifold mount for the m54b25. Just add cats if your trying to be legal.


sbcrazy 08-10-2013 10:55 PM


CrisB02 08-10-2013 11:43 PM

Re: m3 stock headers on 325 m54b25
What is up with the pic must see!!!!!!!

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