Earl said:

They scrap them because of the valuable metals inside.

This. There was a local guy who would advertise on CL, business name was Competitive Core, and would pay well for the older larger cats like from an e30 (Snap remember "catman"?).

There was also a problem a while back or maybe it was urban myth about folks coming out to their lifted pickups/SUVs and finding the cats cut out of the exhaust. Easy to crawl underneath with a cordless sawzall, make a couple quick cuts, and sell to a less than scrupulous scrap dealer.

YoungCR said:

The exhausts are really easy to drop on these cars, although I don't know what your header setup looks like. Wouldn't be a bad idea to drop it all and make sure the exhaust manifold gaskets weren't reused and part of the current problem. 

Good Call. I'm planning on doing some work on it tomorrow.  I keep y'all updated.

straight6pwr said:

try wrapping the holes with exhaust wrap to see how it sounds. you wont have to drop it for that. (if they are accessible)

That's what I was going to do originally, but it is too tight to the undercarriage to get above it.  I'll drop/weld it this weekend and let y'all know how it goes.

straight6pwr said:

unless you have a moral obligation towards our environment, then don't bother with the catalytic converter. but if its still on the car, i'd leave it. if the car is lacking one completely and the PO replaced it with straight pipes, I'd go with a resonator instead - it will make the car sound better. resonators will take some the 'harshness' or 'rasp' out, although the m20 doesnt have a lot of that to begin with.

you didnt explain what is on the car - what did the PO modify?

m42b32 said:

Exhaust leaks are 100% the reason your car doesn't sound good. 1st thing I'd try is just drop the exhaust and weld up any holes. If you still don't like the sound, add a resonator like Dan said. It will have the same (if not better) effect as a cat and will cost a lot less. 

Currently it has aftermarket header with straight pipes back to the stock(?) muffler. I plan on welding up the holes, but don't want to have to drop the exhaust twice.  I hadn't looked into resonators.  Thanks for the tips, I may just weld the leaks this weekend and see how it sounds.

you didnt explain what is on the car - what did the PO modify?

Earl said:

They scrap them because of the valuable metals inside. An aftermarket cat would do you just fine. Otherwise you can weld it up as is and forget the cat all together. 

Have you heard an E30 without a CAT? Do they sound good? Right now mine sounds terrible.

No.

Description

Supp.

Qty

 From 

 Up To 

Part Number

Price

Notes

01

RP-exhaust pipe catalytic converter

1

11761716743

$2227.41

ENDED

I was looking at a universal one for $99.  I wonder if it's worth the time to weld up the leaks and see how it sounds.  Do you have a cat on your 325? The way yours sounds is exactly what I am looking for.

http://www.realoem.com/bmw/enUS/showparts?id=BB13-USA-07-1991-E30-BMW-325i&diagId=18_0170

Here's what the rear section should look like

http://www.realoem.com/bmw/enUS/showparts?id=BB13-USA-07-1991-E30-BMW-325i&diagId=18_0171

Suppose we could have looked this up last night

Andrew