951 cat-bypass
 

hey, i have a 951 and i am looking to do a cat-bypass. i can either have a friend just weld in a pipe for me or i can take it to an exhaust shop. does any one have any experience here and how much power am i looking to gain. the car is bone stock, looking to do chips and boost enhancer

I have heard its something like 15 HP for hollowing out the cat. I would get a testpipe to make this job easier. What year car do you have?

1987

Does NY do vehicle safety inspections? If so, they'll be looking for a cat. You may want to consider welding the old cat shell onto the outside of the straight pipe.

Go for it, Put shell on straight pipe.
 

I agree with Coilover944,
In NY that is part of the safety/emission inspection.
The police really need to see the shell.
Otherwise good torque gains, low to mid rpm. Improved Turbo spool up time...
I say go for it...;)

Later

I want to do this to mine soon as well, let me know what you think of the gains if you do it.....And you can never ever go wrong chipping :)

The biggest gain you will see is faster spool up.

Supposedly the metro area is changing the emissions testing in 2011 for pre-94 cars (heard about this a number of times earlier this year) but ive not heard too what yet. From what ive heard it will most likely be an idle sniffer test similar to what they do for AWD cars now. With that said a perfectly tuned car might pass the idle sniffer but depending where you take it they may actually look for a cat.

this is to zhengwei, when you said that you have to remove the inner sleeve, what do you mean, you cant just cut the pipe and weld a pipe in?

Now that mine is finally all bolted up, the cat looks perfectly fine over the 3" SS inner pipe, if someone was to look. What they probably wouldn't like seeing, would be the open waste pipe, pointing straight down, next to the cat. But if they checked, they would see that there was nothing coming out of it. I would say that I switch it over when I go to the track. But the reality is that it will open up (Enter The Dragon) at full boost, 20psi.