Exhaust Rules Question: Weird Cat

#1

I was planning to have a simple race exhaust made so I wanted to be sure (1) that it’s legal and (2) that it’s a decent design that will give reasonable performance. I have the cat/downtubes off the car and after looking at it this thing doesn’t look like the other pictures of stock E30 cats. Here are some pictures (sorry for the clutter in my shed… )

This is off of a '90 325is but it’s very possible this is an aftermarket piece. It obviously joins the two downtubes into one large pipe prior to the cat. If I were to use this, as per the rules I’d cut the large pipe immediately before (coming from the engine side) the cat and probably run one large pipe back to a race muffler(s).

(1) Is there any way this would be considered legal? From my reading of the rules, the answer would be no since they say nothing about replacing the cat/downtubes. Normally I’d go to a salvage yard and just grab a stock replacement, but unfortunately selling a used catalytic converter is illegal in California. Supposedly all our local salvage yards remove the cat as soon as the car comes in. Any advice in this area would be appreciated. It seems I’m somewhat screwed here. A new factory piece would be major $$$. :ohmy:

(2) If this particular cat happens to be legal, is there any downside (performance or otherwise) to running one large pipe all the way back versus two? I’ve been reading through the archives and (since most everyone seems to have the stock cat) the most common setup seems to be two pipes back to either two mufflers/glass packs or a two-into-one muffler.

Thanks in advance for the input,
-Joe

#2

I will give this a shot but I am sure someone else will know better. It looks like someone cut the down tubes from the manifold and installed the new cat. Now for racing you don’t need the car but you do need the crossover that seems to be missing. I think you need to find a stock crossover or a new set of down pipes with the crossover. Then you need to install a duel pipe all the way to the back with a set of cherry bombs. You have to go back with the same number of pipes you started with. If it is two all the way back you must have two and cannot conver to one.

After you build the new exhaust, I would just add some flanges to the new system and to the system you have now and install the cat when you need it on the street. If the car does not see the street then don’t worry with it.

HTH,

Michael O.

#3

Wow, looks like someone went cheap on your car’s cat replacement.

#4

actually the rules allow you to modify the exhaust from the stock cat location rearward, so you could do a single pipe if you wanted to.
cheers,
bruce

#5

Hi All,

I wanted to follow up on Michael’s posting (thanks Michael!) on using a flange setup to swap between a street legal cat exhaust system and a track system. Does anyone have any pictures they could share on how they’ve done this?

Doug J.

#6

Thanks for the input. I’m in the process of trying to find a stock cat/down tubes. If anyone knows where I might be able to get a used one, I’d appreciate the help.

#7

just to clarify - you don’t need the stock cat if you don’t want it.
cheers,
bruce

jschmid wrote:

#8

jschmid wrote:

[quote]Thanks for the input. I’m in the process of trying to find a stock cat/down tubes. If anyone knows where I might be able to get a used one, I’d appreciate the help.[/quote] contact Al Taylor from this board

#9

jschmid wrote:

Just to re-inforced what Bruce said, the rules allow you to change the exhaust from the cat (including the cat) back. You can leave that cat and run a straight pipe all the way to the end.
I’m not sure about the "Y" pipe before the cat. You might be able to find a stock down pipe form a junk yard.
Now the questions are:

  1. Do I want to keep the cat?
  2. Do I want a straight pipe to the end or add a "cherrybomb"?
    My answers:
  3. Keep that cat
  4. Straight pipe (track car only), cherrybomb (street and track)
#10

People are always parting out cars in CA on:

www.r3vlimited.com

&

www.e30tech.com

You should be able to find some stock pieces somewhat local to you.

JP

#11

I have the exact same setup on an '89 325i. Right down to the same size/shape cat, the narrow incoming Y and the wide exiting Y. Although, with 227k miles, it is possible that a previous owner had it replaced with an aftermarket one.

I am about to replace my system (failed emissions inspection & I drive it on the street occasionally).

I was thinking about a glasspack with a cutout setup before the muffler. Any opinions on this?

Patton - you mentioned a shop in Atlanta that does this work. Can I get that contact information from you?

Thanks,
Erik

#12

Call me at 770-886-2500 and I can give you the details. Regards, Robert Patton