Project E36 323is: Building the Poor Man's M3, Part 4 
- Exhaust

By Jonathan Lawson

Now that our E36 323is is hustling through the corners a bit more sure-footedly, there's one thing that seems to be missing.  A soundtrack!  While our car is not packing the most powerful engine in the world, it's still got a bullet-proof and (potentially) great sounding BMW M52B25 inline 6, yet it's almost as if the factory put the whole car on mute.  The engine loves to rev, and is sewing machine smooth at any RPM thanks to the motor's inherent balance, but it really feels like it wants to sing a bit louder, and who are we to stop it?
E36 Corsa exhaust and M3 center section
The good folks at Corsa have just the cure for us.  Pictured above is our new exhaust system for Project E36 323is.  That's the Corsa cat-back exhaust in the background and our "new" E36 M3/328i center section in the front.
E36 323is center exhaust section
With the design of the 323is center section having dual pipes going down to a Y before the cats, we already knew we wanted to change over to the fully-compatible M3/328i section in order to get some better flow while maintaining the catalytic converters (legally required in CA).  
E36 M3 vs 323is center section comparison
This is a better view of the center sections side-by-side.  You can clearly see the difference once you get to the cats.  What once was a Y is now a set of twin pipes all the way back on the M3/328i version.  Not only does that help to increase flow a bit, but it also just happens to open up a very wide range of choices in cat-back exhausts.
E36 Corsa exhaust versus factory 323is comparison
Our exhaust choices were plentiful and many of them met our criteria for weight reduction, which isn't too hard when comparing to a bulky OE muffler as shown above.   Our stock muffler was 43 pounds, so we managed to cut off around 10 pounds with the Corsa, and if looks matter to you, this one's got the goods, especially with the new Diamond Black finish on the tips. 


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Pablo Mazlumian
Pablo Mazlumianlink
Saturday, June 15, 2013 1:37 AM
5.7whp peak to peak (and looks like maybe around 7-8 whp peak gain up top with 11-12 lb-ft at 3k?)...I've tested over a dozen on E36 M3s and have never seen that (not until going cat-less), so that center section must have helped. And It's even a more significant gain when considering the near-stock 140's power level. Impressive.
Dan Barnes
Dan Barneslink
Sunday, June 16, 2013 6:51 PM
Wuz also gunna comment on the center section probably being worth at least as much as the cat back.

Is Mike losing sleep over the sharp angle cuts on the RH tip?

My last memory of my E36 is hearing the new owner get on the throttle (120k Supersprint cat back) out of sight a block over on Broadway and thinking, "Hey, that sounds really good! I've never heard my car from the outside before."
Wednesday, June 19, 2013 5:48 AM
Ha,ha,the angle cut pipe bothers me too.
Wednesday, June 19, 2013 5:52 AM
So you lost weight on the cat back. . . what'd you gain from the center section? :D

Are the smog nazis smart enough to see you've swapped in an M3 pipe? If they did, would you catch crap? Just curious, my guess is it depends on who's doing the inspecting and what side of bed they rolled out of that day.
Nick B
Nick Blink
Wednesday, June 19, 2013 6:17 AM
@Supercharged - Just going to play it dumb when it comes to the CA Smog Nazis, I've taken in some "questionable" vehicles to my local smog shop (nothing crazy just stuff like non CARB intakes) and they've never said anything.

Wednesday, June 19, 2013 6:50 AM
I don't know if it would be a CARB issue or not. It's got cats, they're CARB-certified (OE!), they aren't aftermarket, AND it would still pass the sniffer test, so it should be a moot point. Of course YMMV, and do this at your own risk, etc. ;-)
Wednesday, June 19, 2013 11:14 AM
BMW has the strangest OEM muffler fabrication methods.
Wednesday, June 19, 2013 12:11 PM
Two problems:

1. Used cats are illegal to install. Ignorance (claimed or otherwise) helps here.
2. The monkey at the smog shop is going to look in the book, see the number of cats its equipped with, then look under and count. Since this has independent cats, the monkey may end up with a higher number than the book says. Going to a shop that has tight confines around the rollers and no jacks/lifts in sight will be a bonus here. The lowered car also helps.
Nick B
Nick Blink
Wednesday, June 19, 2013 1:10 PM
@Rockwood - Every party needs a pooper that's why we invited you! But in all seriousness you are 100% correct. I'm banking on the fact that 1. It has cats 2. My local smog shop has overlooked non CARB intakes in the past (and it's a test only BTW) 3. It should still pass the sniffer no problem 4. there are no lifts at my smog place as I stated earlier it's test only, it's about the size of a 1 car garage. 5. Ignorance

I guess we'll find out in Oct when my registration comes due.
Tuesday, October 14, 2014 5:04 PM
Getting ready to swap my 323iS exhaust for the M3s and a guy from Bavarian Autosport told me to ask someone who has already done this swap what the emissions effects would be considering the different number of sensors. Will this turn on the check engine light? Can I just delete the "extra" sensors? I have no idea how this will turn out. I'm in CT btw, and it seems some of the CA guys here may have stricter regulations.
Sunday, October 11, 2015 6:57 PM
I read all the articles for the 323is project and got the idea to swap out my no longer functioning cat for an 328is OEM replacement front section/dual cats replacement also. I had a question about the sensor issue. Since I just replaced my O2 sensors I planned to use one of my old post O2 sensor to plug the extra hole in one of the dual pipes, drill a hole , weld a nut for my pre-cat sensor to go into like the OEM single pipes had. There are no pre-cat sensor ports on the unit I have coming , the pre-cat sensors ports are on the exhaust manifolds on the 328is I used as the vehicle I was ordering the replacement for. Since my pre-cat sensor will only be monitoring half as much exhaust gas as before, will it cause my engine management computer to go lean, rich or stay about normal since that sensor feeds adjustment info to the fuel injection. Any help with this question from anyone would be of great help. It was only $50 bucks more for the 328is OEM type replacement cat units compared to a direct fit 323is , so I opted to go with a total dual set up to the muffler with twin inlets and twin outlet pipes to finish off my exhaust. Thanks for such good articles, great ideas and helpful pictures for reference.
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