911Jetta

That's what I've read in the past. The cat material holds a lot of heat (necessary to keep the cat internals at a certain temp), therefore a shield is needed. A bypass doesn't hold the heat, so no shield needed.

Laker,
No worries, I was mostly interested in knowing if people didn't notice the smell with a Wong chip?

Joe@Fabspeed

Porsche added heat a shield to the factory catalytic converter that is attached to the bottom of the catalytic converter. These are there so in case you are driving and parking on tall grass the car doesnt catch fire. The heat shield is NOT to protect the left rear tire under any circumstances.

As you all now Porsche AG overengineered and overthought all heat shileds on 964 engines. It is common knowledge that all that foam silver inuslation wrapped tightly around the complete engine fries the valve guides.

Fabspeed 964 catbypass pipe/ Europremuffler is a muffler resonator that is wrapped internally with T304stainless steel wool and then rockwool. This insulates the pipe. The bracketry that Porsche welded on to the stock catalytic converter often cracks and fails and then vibrates. If you have ever worked on these 964 cars the brackets and heat shield on the 964 stock OEM cat is sharp, ugly and a PITA. It is uncessary and I deliberately eliminated 15+ years ago. Trust me you dont need it under any circumstances and the 964 catbypass pipe or sport catalytic converter looks smooth and clean under the engine. On certain customers 964 cars I have even cut-off and removed the silly brackets around the catalytic converter.

FYI- Porsche overthought the 964 car and Porsche Germany installed no undercar heat shields to their catalytic converters from all cars after the 964. So IMHO Porsche decided it was an engineering waste of time. There are no heat shields under the catalytic converters on:

911SC, 911 3.2liter Carrera, 993, 993TT, 996, 996TT 997, 997TT and all GT3 cars.

Silvertarga

I read in the 993 forum that there is a difference in opinion as to use of the 02 sensor with a cat bypass (of course that is OBD II)

Is there a problem with using the 02 Sensor in the OBD I 964 series with Cat bypass?

NVM used search and it appears that the O2 sensor is the way to go

Jimjacqmx5

Another option....

Maxspeed motorsports have a full decat and also a 100 Cell Cat which will give you the performance with a slight gain in noise but no smells and it is still legal on the road..
I have the 100 cell CAT with a primary bypass and the maxspeed larger exhaust tip and I get comments from all sorts of Porschephiles about how nuts it sounds....

The sport cams help as well....

Cosmos99

I have a SW chip and a fabspeed bypass and have never noticed a fuel smell. Exhaust smell yes as there is hydrocarbons not being burned off by the cat substrate but fuel smell no.

Michael D'Silva

Awesome thread.
I just bought the fabspeed cat bypass, realised it had not tabs, then wrote to Fabspeed...
Should have found this thread first!
I'll be glad to be rid of that bloody heatshield.

My only question is that the exhaust is fairly close to the left rear shock absorber... is the proximity of the heat detrimental to the shock??

greg1990964

What do you mean by tabs? For shields? No, the shields have nothing to do with shock or tire. Just over engineered.
My new fabspeed cat bypass comes tomorrow!

Michael D'Silva

cool, thanks for speedy reply....

greg1990964

I sit in my easy chair in the garage between tasks and look at rennlist. That's why it is quick. Ha. Do you have a primary bypass? That's the combo I will be running with the cat bypass.

Tmistry

No downside that I've experienced. I have a fabspeed cat bypass and a cup pipe. Just a gorgeous resonant burble at idle and a brutal scream at 4000. Love it. Here's a link to last year's first start. There's a slightly pronounced valve clatter, which isn't abnormal, but it decreased to my satisfaction after I changed to 20W-50 viscosity from 15w-40.

StopLookGo

I was thinking of having a local muffler shop replace my cat converter with a stainless steel pipe but now I think I'll have them replace it with straight flow muffler. I run a long j pipe and it's pretty loud as it is.

greg1990964

Doesn't want to play. Maybe it's my phone. I will try later once I leave my garage. Been in here since the morning. Ha. Compound and polishing black coupe after suspension upgrade.

StopLookGo

carpeted garage

John@Fabspeed

We're excited that you're so excited, Greg! Make sure to post some sound clips for us!

greg1990964

Funny you say that. Like everyone else I just took the before video. I am slapping the pipe on now. Should of swung a deal and bought 2 at once, one for the coupe also if I like the sound.
One suggestion: I appreciate the new gasket and the front 4 bolts, but my bolt on the muffler clamp just snapped. Wish you guys included that one also!