cat pipe bypass opinions

Rick V · 10-15-2005, 04:36 PM

I would like to hear the pros and cons from people who have run a by-pass pipe in place of thier cats. I have an 82SC that I am thinking about dumping the cat out of. My main concerns are the low end torque loss and the volume increase. Volume being the pitch more than the decibles. I don't want a high pitched car. And the recomendations are?

jtratza · 10-15-2005, 04:59 PM

I switched mine out years ago with a Bursch bypass. Deeper tone. Less heat on the left side. A few pounds less weight. Probably a couple of horses added (because the cat was 15 years old at the time) but tough to tell. The only other advantage is you can save the original one to use for NOx testing. I recommend doing it but don't expect some big leap in performance but then you seemed more concerned with low end loss which I don't think is a big issue with taking it off.

slangager · 10-15-2005, 05:29 PM

I just replaced mine last weekend. At first, I was not that impressed. I didn't feel a noticeable difference when I first started out and almost felt like I lost horsepower. Also, I was expecting a raspier sounding exhaust without the cat and the car is only a tad deeper.

Now that I have been driving it for a week I notice the additional power on the top end. Of course, most of us do not always drive around at high RPM's but if you do then you'll probably like this upgrade.

To be honest, I'll probably go back to the cat eventually. I was curious, just like you, but I don't think it's worth the extra few horsepower and loss of low end torque. Plus, you're poluting the environment more (not like 911's are eco friendly to begin with) losing low end torque and risking an expensive ticket if caught.

Anyway, that's my opinion....If you're anything like me you'll need to put one on just to see for yourself but don't expect the 20hp I was.

Stuart
79 SC

jtratza · 10-15-2005, 05:47 PM

Don't entirely agree. While the performance dif is not noticable the lower exhaust tone is. What I have noticed is the enviro tests are still coming in below state and City of Houston standards without the cat except for NOx and its very close. Some of the credit goes to the hot wire sensor from APE. I'll post the before and after results next month after last months rebuild. My experience is these cars ( mid to late 80's)can burn very clean except perhaps for NOx if kept in tune.

kepperly · kepperly's Garage

My modification was to remove the B&B exhaust and install a Bursche Cat bypass and one in one out muffler with a Steve Wong Chip. My 87 is a differant CAR now and lots more fun to drive.

Keith Epperly 87 slant nose turbo look carrera cabriolet

Rick V · 10-16-2005, 10:36 AM

I am thinking more about the B&B header and muffler setup. Winter is coming and I need some more projects. hahahahaha.

mikemdd · 10-16-2005, 10:49 AM

I think you will get different opinions from Carrera and SC owners. Different fuel management systems, engine displacement, etc.. I replaced the cat on my 81SC with a euro-type pre-muffler (aka cat bypass) for the sole purpose of being able to richen the mixture to run better without ruining/plugging up the cat. Frankly, the sound change was minimal. Peformance change is also not real noticeable. However, it runs much better with the mixture a little fatter. I just had it smogged, and it passed with no problem without the cat. Just my experience.

Mike

fuelie600 · 10-16-2005, 01:13 PM

I would guess it will be related to the condition of your cat before you clean it out.

I installed a euro premuff and one of Ben's M&K exhausts on my 87. I did them both at once, so I can't comment on just the premuff. I can say there wasn't that much difference in performance. If there is any difference in feel, it's in the higher rev band. The engine seems to rev more freely.

I'll try one of Steve's chips one of these days....

Rick V · 10-16-2005, 01:27 PM

The issue of smogging isn't a concern for me. We have no testing where I live and I am a state inspector. The only bennifit I recieve for all the BS I have to put up with from the customer and the state police dept.

kepperly · kepperly's Garage

Rick, it would be my advise to stay away from the B&B offering the noise is not right and the quality is not what one would expect for that much green. The bursch set up is the RIGHT sound and doesn't blow apart like the B&B. Yes I am experienced like Jimmie Hendrix used to say.

Keith Epperly 87 slant nose turbo look carrera cabriolet

TCB · 10-16-2005, 02:06 PM

On my 84 carrera I have the Dansk pre-muffler and the Dansk sport muffler. A lot less heat on left side and the sound is great. Not too loud in the car but a nice deep sound. Can't say I noticed that much difference performance wise, I was mainly after the sound. I'm happy.

cyprusx · 10-16-2005, 04:40 PM

Fabspeed 911 Euro-Premuffler Catbypass Pipe: $260
Used muffler from eBay: $50
2 hours to gut as per instructions on this site: $0
Local muffler shop to weld up: $20
Tone: Priceless

Volume is very mellow when not on it, very mellow. When you get on it, it screams like a wild banshi, very nice sounding. Store you stock muffler and CAT and swap it back anytime in an hour or so. I believe this is the best "known" secret that more should attempt. Comparing the price to the alternatives makes it a no brainer...

JBO · 10-16-2005, 05:28 PM

The reduction in engine heat, cooler running and drop of a few pounds make the change worthwhile. Made my GHL muffler sound even better. No noticeable performance gain, but the other benefits are well worth it.

Tigerrat · Tigerrat's Garage

Tom - So I'm curious ..... Are you installing the cat each year for Houston tests or not? Thanks, Ken

jtratza · 10-16-2005, 06:33 PM

Tigerrat, Each year I put the cat back on to pass the test. Takesa 15 m minutes. Since I just had the engine rebuilt I may try to pass without it. It almost passes NOx without and will pass all the other tests.

scotricker · 11-12-2017, 07:42 AM

See? I searched !

While my engine is out. 1978 911 SC, I was thinking about how easy it would be to bash the guts out of the cat, while I have such easy access. Or save it all as-is, and get a real by-pass pipe? Free butt-dyno improvement? I think cat bashing would be funner.

Flojo · Flojo's Garage

Quote:

Originally Posted by scotricker

See? I searched !

While my engine is out. 1978 911 SC, I was thinking about how easy it would be to bash the guts out of the cat, while I have such easy access. Or save it all as-is, and get a real by-pass pipe? Free butt-dyno improvement? I think cat bashing would be funner.

get SSI. all on the plus side (weight, heat, sound, performance). case closed

kyngfish · kyngfish's Garage

Quote:

Originally Posted by Flojo

get SSI. all on the plus side (weight, heat, sound, performance). case closed

I thought the consensus was that SSI wasn’t all that great for the 3.0/3.2

Flojo · Flojo's Garage

he has a 82SC...

Stutzdriver · Stutzdriver's Garage

My suggestion is to SAVE the old CAT, clean it up and store it. These are no longer available, you can only get universals and if someone needs a cat to pass emissions (or for Concours), the original CAT has value. I'm in the exhaust business and I know of what I speak....

My 84 Targa is getting a cat pipe this winter, I'll store the 56,000 CAT just in case the emissions regs change to match Californis, NY and some others...