Stock Cat Modification

[Dominic]

Is it possible to trim the stock cat outlet back to where its a 3" outlet and connect the sucker up to a 3" pipe? What do you people do when you run the stock cat and run all new 3" piping?

[99Camaro99]

my stock cat opens up to 2.75" outlet. It's possible, just MAKE SURE whoever does it puts the O2 sensor back on right.

edit...whoops, I meant it's opened to 3" but I have a 2.75" I-pipe to a 2.5" muffler...everything just keeps gettin smaller :D

[ June 14, 2002: Message edited by: 99Camaro99 ]</p>

[Dominic]

<blockquote>quote:</font><hr>Originally posted by 99Camaro99:
edit...whoops, I meant it's opened to 3" but I have a 2.75" I-pipe to a 2.5" muffler...everything just keeps gettin smaller :D

[ June 14, 2002: Message edited by: 99Camaro99 ]<hr></blockquote>

Thats probably a good thing it gets smaller, because as the exhaust flows down the pipe it cools and the pressure drops. If the pipe continuously narrows it will have the same pressure from the cat to the muffler - very cool [img]smile.gif[/img]

Did you modify yours to open up that wide or is that how it came?

[ June 14, 2002: Message edited by: Dominic ]</p>

[Shadly]

Careful, if you ever have to pass smog in CA, don't touch your cat.

[Dominic]

<blockquote>quote:</font><hr>Originally posted by Shadly:
Careful, if you ever have to pass smog in CA, don't touch your cat.<hr></blockquote>

I had to get a smog test when I entered CA sadly - but I passed no problemo. I figure modifying the cat (cutting off the 3" to 2.25" adaptor thats built on the end) would still be legal since I am in effect not touching the cat, only the pipe flange adaptor. Thanks for the tip though!

[Guardsman]

In the service manual drawings, the s-pipe is part of the cat, so it is probably considered part of the cat for legal purposes (remember, we're talking about California). Anyways, if you're over 50,000 miles, it doesn't matter what you do to it, so long as you have the emissions stuff in something that looks close to stock form, and it works.

[99Camaro99]

Dominic originally the stock cat is a 2.25in and 2.25out but basically what he did was he jammed a 3" pipe into it to open it up. Not too much rocket science to it. :D Just MAKE SURE the O2 sensor is put back in properly or expect SES codes and possibly tranny problems. Long story...but all is good now.