cat gutting question

[babyJ]

I was wondering and I tried a search but couldn't find anything
But If I gut the cat on my 99' gst will the ses light come on??
Will it make any difference if performance??

 

[larryd]

this should really go in turbo performance which is where ill move it to.. this forum is only for SITE related questions..

to answer though it may or may not cuase a CEL.. some people have problems with the light when they remove the cat and others dont. IMO your better off just buying a test pipe.

 

[babyJ]

thanks and sorry for posting in the wrong forum
I have one sitting here and wanted to try it.

 

[larryd]

you have one what, a regular cat?

 

[babyJ]

I have a stock cat sitting here...

 

[HighPsi91]

Dont gut cats. They do not flow very well at all. You are much better with a test pipe.

 

[BatmanGSX]

Originally posted by HighPsi91
Dont gut cats. They do not flow very well at all. You are much better with a test pipe.

I disagree. It's a good free mod. I noticed that I was able to get boost at the line after the cat was gutted. This was on an otherwise stock exhaust system.

 

[HighPsi91]

Originally posted by BatmanGSX


I disagree. It's a good free mod. I noticed that I was able to get boost at the line after the cat was gutted. This was on an otherwise stock exhaust system.

How much quicker and faster did the car run? I have seen for myself that gutting an otherwise healthy cat hurt top end power even on a naturally aspirated car.

 

[BatmanGSX]

I don't know. But if I could get boost at the line, and never could before, obviously it was flowing more. How can more flow = less power? I don't think it can.

 

[HighPsi91]

What makes you so sure a gutted cat flows better?

 

[BatmanGSX]

Because, right after I did it I was able to free rev the engine and get up to 7psi of boost. That is for sure indicative of more flow. Before that I could get maybe half a psi.

I don't see how a gutted cat could flow less than an intact one. I mean I can see how due to its shape how there could be reversion or something but overall I think it would flow a lot better than two bricks with a bunch of tiny holes in them.

 

[HighPsi91]

A few years back I thought the same thing. I ripped a fairly new cat off my Z-28 and proceded to knock it out. I drove the car and it felt a little stronger at lower revs but up top it lost power big time. Needless to say I was both surprised and pissed. A lesson learned. 1 expensive cat + lots of time to pull and gut = much less power than a $15 straight section of pipe. A few of my freinds gutted their cats on their DSMs and had similar results. Obviously the only way to proove or disproove any of this is to take backpressure readings before and after gutting a cat and test it under various rpms and loads.

My theory is on a turbo car the loss is not as great because the initial reduction in backpressure will help spool the turbo. Therefore you will potentially make more power in a certain operating range. But I still feel the net result is either near zero gain or more likely a loss if looked at through a full pull.

 

[BatmanGSX]

I'd say that on the N/A car that you were probably at a power level where the engine didn't like loosing the backpressure. On a turbo car we have the turbo itself to provide adequate backpressure.

It may be worth testing since some people like to gut their 3" cat's to fool law enforcement or e-test techs. Gutting a stock cat you have sitting is no biggie but gutting a brand new, $150 3" cat is a big deal if you don't get anything out of it.

But I agree that a straight pipe will of course beat the gutted cat due to better laminar flow characteristics.

 

[HighPsi91]

It was a 350ci V8 feeding into a single 2 1/2" cat.... it had more than enough backpressure gotta love GM.

It would be an interesting test though. I have seen so many people buy a nice new hi-flo cat and then knock em out (I was guilty of it myself), just makes me cringe every time I see it.

 

[babyJ]

Thanks for the help guys.. I was also wondering if the cel light
would start to shine after I did it??

 

[doug]

Originally posted by larryd
to answer though it may or may not cuase a CEL.. some people have problems with the light when they remove the cat and others dont.

 

[babyJ]

I saw that post but I'm not removing it.
I'm just going to gut it...
I was just curious as to if anyone has done
it and what was the outcome...

 

[doug]

Emissions-wise, gutting it and removing it are the same. The rear O2 sensor would read "un-catted" air either way.

 

[nine5raptor]

if you want to have the cat-look, take the outer casing and weld it onto a test pipe...straight smooth flow and looks like a cat for visual inspections