The following is a purely fictional account of what might have occurred if I had a race pipe fabricated for my car in place of my cats, which of course I did not do given the legal implications.

I have a RUF exhaust with 100 cell cats. RUF uses a stock exhaust housing and modifies the internals. Therefore, the pipe between the turbo and the baffle chamber of the exhaust is stock (at least it appears to be), with 100 cell race cats in place of the stock 400 cell cats.

I hired a local exhaust shop that specializes in high performance exhausts to fabricate a “race pipe” to replace the RUF pipe housing the race cats between the turbo and the baffle chamber. I wanted to retain the RUF pipe so that I could return the exhaust to its original form at some point in the future. They removed the exhaust from the car and cut the RUF pipe housing the cats at the point where it meets the chamber. The cut was very clean, the cats are unaffected, and I can easily reattach the pipe in the future. Then, they fabricated pipes out of stainless steel that expand from approx 3 inches at the turbo to approx 5 inches at the baffle chamber. They also fabricated flanges to attach the pipes to the turbos (the RUF flanges remain on the RUF pipes). The job took much longer than they originally expected, but they took the time to do it right.

The results are amazing. The turbos spool earlier and noticeably faster. Small blips of the gas peddle produce immediate .6 bar. Throttle response is better. Moreover, I am seeing steady 1.3 bar at WOT, whereas previously 1.2 bar was the norm. I did the testing in 83 degree weather . . . can’t wait to see what kind of boost I get at 60 degrees.

I was very concerned that removing the cats would produce an unacceptable increase in volume. Much to my surprise, the car is only marginally louder, and still well within acceptable limits -- much quieter than certain other exhausts I have heard with cats. Given that the RUF exhaust is quieter to begin with, I suspect removing the cats on other, louder exhausts, will cause greater volume increases.

Prior to my current Stage V ZC turbos, I was using a K16/K24 hybrid produced by Innovative. One of the things I loved about the Innovative turbos, in addition to their phenomenal performance, was the audible whine they produced -- there is no greater sound than the whine of a spinning turbo. Prior to removing the cats, I wasn’t able to hear my ZC turbos spin. With the cats removed, the whine is back, and it sounds great!

Given the nature of this mod, I have intentionally omitted the name of the exhaust shop from this post. However, if any So. Cal. TT owners are interested in having a race pipe fabricated, I highly recommend the shop I used, and I can put you in touch with them by PM. Given that every exhaust is so different, the pipe must be custom fabricated while the car is at the shop.

Of course, this entire post is pure fiction, as I would never dream of removing the cats.

Craig

 

I always figured most of the gains from an aftermarket exhaust system came from changing the cats from 400cell to 100cell cats. Knowing that I can get a good quality high-flow cat for $90US each, it would be a relatively easy and cheap mod to cut the stock cats out and replace them with high-flow cats.

This would increase power (with volume increasing marginally) would be well worth the $90 x 2 = $180 + $120 install = $300 TOTAL for everything.

I figure it would lead to more than half the gains of going with an exhaust system, but at a price everyone would enjoy!

What do you guys think?

- KJ

 

We have been selling a version of our exhaust with Cat Bypass Pipes for a couple years now, and we have had the same experiences you have!! Spool is great, it doesn't get much louder than 100cell cats and the little flames are an added bonus .


Now all you need to do is step up to the REAL race pipes:
FVD Race Pipe Video
These things spool in half the time my exhaust with no cats did and man the whistleing of the turbos is unbeatable!!!
Evan

 

Heya Craig,

How did you get by like that? Did you get new programming???

 

New programming? I am using a program made by GAIC specifically for the Stage V ZC turbos. I did not modify the prgram for the cat removal. The check engine light hasn't come on yet, and I don't recall whether the GAIC program disengages the check engine visa-vie the O2 sensors. If it doesn't, and the check engine light comes on, I will ask for this tweak when I get the new GIAC program for my new intake (scheduled to go in next week). In the meantime, I have a OBDII scanner I picked up for $140 at a local parts shop that enables me to reset the check engine light (after reading the code).

Craig

 

I just figured if you went "catless" you'd throw a CEL?