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Cats after mufflers?

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Old 02-28-2007, 11:32 AM
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Default Cats after mufflers?

Is there anything wrong with having the cats after the mufflers? The reason i ask such a rediculous question is that i am considering a setup like TheBlurLS1s old TD-under axle setup. If you're not familiar with it, its a tsp true dual system with the turndowns cut off, and a removable set of under-axle pipes that connect here and extend to the rear. Well, how about having the cats in the extended pieces? That way you can run dumped and loud, or quiet and legal.
Old 02-28-2007, 11:51 AM
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wont be too legal because cats have to be in a stock location. If you were to if youre concerned about power and "legality" just weld some cat heat shields onto your piping.
Old 02-28-2007, 12:20 PM
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won't work anyway because the cats won't heat up nearly enough to do what they're supposed to...

when I do my Y-pipe basically my cats will be directly off of the headers, most efficient way to do it as far as emissions are concerned
Old 02-28-2007, 12:35 PM
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Definitely won't be legal for the reasons stated...and if you want to follow the law to the letter, the cats can't be moved from the factory location, so even if you have cats on long tube headers at the header collector, they are still illegal in the strictest sense of the law (even though it may still pass emissions).
Old 02-28-2007, 01:50 PM
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very well then, lol. That answers that question.
Old 02-28-2007, 01:51 PM
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Looks like i'll be doing TheBlurs old setup, only minus cats!
Old 02-28-2007, 01:52 PM
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Wouldnt it sound a little weird with the cats after mufflers?
Old 02-28-2007, 02:19 PM
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Originally Posted by MeentSS02
Definitely won't be legal for the reasons stated...and if you want to follow the law to the letter, the cats can't be moved from the factory location, so even if you have cats on long tube headers at the header collector, they are still illegal in the strictest sense of the law (even though it may still pass emissions).
lol!,..I just learned that a month ago! It doesn't make sense to me!!!! Why the hell would it matter where the cats are located? A cats a cat,...no matter what the location is right?
Old 02-28-2007, 03:44 PM
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Because cats reply on tempature in order to properly burn off the emmission from the exhaust. The further away from the manifolds you get the lower the temps.
Old 02-28-2007, 03:53 PM
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Originally Posted by Sneakyws6
Because cats reply on tempature in order to properly burn off the emmission from the exhaust. The further away from the manifolds you get the lower the temps.
yup--that far back , they really won't be doing anything at all.
Old 02-28-2007, 04:00 PM
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Originally Posted by Sneakyws6
Because cats reply on tempature in order to properly burn off the emmission from the exhaust. The further away from the manifolds you get the lower the temps.
Hit the nail on the head here
Old 02-28-2007, 04:03 PM
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My dad has a '95 Chevy dually with a 454. It's got the hugest cat ever, and its AFTER the muffler, which is AFTER the extended-cab, bone stock.
Old 02-28-2007, 04:39 PM
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Originally Posted by TheBlurLS1
My dad has a '95 Chevy dually with a 454. It's got the hugest cat ever, and its AFTER the muffler, which is AFTER the extended-cab, bone stock.
Really? I've always thought they'd be closer for some reason...I guess if you wanted to change the exhaust, you'd buy a cat-forward system?
Old 02-28-2007, 04:45 PM
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Originally Posted by TheBlurLS1
My dad has a '95 Chevy dually with a 454. It's got the hugest cat ever, and its AFTER the muffler, which is AFTER the extended-cab, bone stock.
You sure about it being the cat and not a silencer like on Dodge trucks just before the exhaust inlet side? No way that thing is factory if so...even my 1991 Chevy had a single cat at the Y just after the cab. Pics?! Sorry I just can't fathom the reality or reasoning for a cat that far back from the factory.
Old 02-28-2007, 04:59 PM
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Originally Posted by Sneakyws6
Because cats reply on tempature in order to properly burn off the emmission from the exhaust. The further away from the manifolds you get the lower the temps.
****!!...wow!.simple yet awsome answer! Thanx!!! Makes sense!

Hey,.....don't some LS1s have cats further back from the manifold on the passenger side closer to the Y-Pipe?
Old 02-28-2007, 05:01 PM
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Originally Posted by WS6 Rampage
****!!...wow!.simple yet awsome answer! Thanx!!! Makes sense!

Hey,.....don't some LS1s have cats further back from the manifold on the passenger side closer to the Y-Pipe?
Yes they do...hence the big passenger side foot well hump that many people despise. Not sure why it was there other than a packaging issue...if I had the time or desire, I'd kinda like to remove that part and make it flat.
Old 02-28-2007, 05:07 PM
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They call it the fat cat





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