Cat guts

[conkeytonk]

Gut the catalytic converter, essentially creating a resonator, replace the cat-back network with an OE and replace all gaskets/hangars as a temporary measure while considering a 3-inch, all-the-way stainless, sport exhaust system (or just give the NA to my daughter and get myself a 951)? Opening the rear has done so much for the Sciroccos. Good idea?

[CJFusco]

There is divided opinion on this topic. Some people say it opens things up, some say that the change in backpressure robs power at certain RPM. My guess is that the torque curve changes, and whether or not it is an improvement depends on the owner's driving style.

[EMBPilot]

My engine is stock so this will give you an idea of where im coming from. and im no 944 expert, heck i dont even race the car or auto cross it but heres my take.

when i bought my car it has some generic 'free flow' $hit can muffler on it, along with a cat delete pipe.

i replaced the muffler with a stock cat back system, i took the car and had a cat welded into the test pipe. i dont recall the size, but it was slightly larger than stock, i want to say 2.25 or 2.5???? not sure... whatever the case it was the size that was matched to the cat delete pipe.

I am 100% sure, the car is more responsive and runs better after putting the very close to stock system back. as well as sounding much better. however, there was a significant decrease in gas mileage. went from 30+ on the highway into the upper to mid twenties.

[ilikemy944]

Do not, whatever you do, gut the cat.
I gutted my cat.
It sounded like complete and total ass-can.
If you must, then weld in a straight pipe - the empty cat will make horrendous noises.

To tell you how bad it sounds, I drove the car once. Then cut the cat off the exhaust and used PepBoys exhaust clamps to clamp on a cheap piece of pipe. It leaks a little at both ends. It still sounds WAY better than a gutted cat.

[EMBPilot]

^^^ X2, agreed! before i had the new cat installed into the pipe, i just had the stock muffler bolted up with the full test pipe. the car sounded better but the cat delete pipe resonated BIG TIME and the car STILL had a can sound to it. half as bad as with the muffler but it sounded awful. big time resonation.

once the cat was installed into the pipe, all the resonations disappeared and the car sounded AND ran great.

[SolReaver]

Converter test pipe would be the way 2 go. If you do take off the Cat. give it a nice hot drive first, after cool down remove it. then wrap and seal the ends to keep the moisture out.

[Slam]

Getting rid of the cat and keeping the stock muffler worked well for me. Cat was just replaced with tubing same diameter as the rest of the system.

[conkeytonk]

Lots of useful opinion here guys…thanks. I’m guessing gutting the cat would create too much resonation so is not a good idea; a straight pipe in its place is an option, not really necessary but will increase fuel mileage; go with an OE cat back system (hey Kevin, is this system stainless?). At this point I’m contemplating weather to leave the cat or replace with a straight pipe. Can somebody overwhelmingly convince me? Of course leaving the cat is less expensive, but at 20 years old, is it still functional? Another question, will any of these modifications affect readings the oxygen sensor sends to the DME (computer)? You guys are a great recourse and I make most decisions about my project based on what comes back, thanks again.

[Razorback1980]

O2 sensor should read about the same as it reads the exhaust ahead of the cat IIRC. Some systems use two O2 sensors one before and one after but I haven't seen or read about any 944 that does that.

[legion]

I gutted the cat on my 951. It virtually eliminated turbo lag. I have no idea what it would do for an NA, but it was a huge improvement for me.

[speedracing944]

I kept my cat intact but opened the muffler, cut out the insides, welded in the straight pipe, welded the muffler back together and repainted it. I like the sound and I think I got a little more power out of it. The guts of the muffler appeared to be pretty restrictive.

Speedy