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99 Trans Am Driver side cat relocation

1136 Views 5 Replies 3 Participants Last post by  GaryDoug
If i were to have the driver side cat relocated about a foot farther down the y pipe, would it at all affect the smog? i know it would fail any visual inspection to anyone that knows stock 4th Gen F-bodys. The reason I ask this is I plan to get electronic cut outs to dump before the cats. the passenger side is no problem. but since the driver side is basically right their at the manifold i couldn't do it the way i planned. and yes i have taken the exhaust off after the cats and it doesn't sound any louder then the pipes i have on it now so e cutouts after the cats is a no. Now if it would aftect smog, would i better off not touching a thing. or getting a off road y pipe?
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the only effect moving the cat further down the pipe will have is a slightly slower cat warm-up time, so it wouldn't affect sniffer tests. if you moved it to the back of the car, it'd never warm up enough to function, but even a foot or two is fine.

some OBD-II cars have a 'slow cat warm-up' diagnostic routine which COULD be tripped if you relocate the cat. lucky for you, it's not mandatory in the OBD-II spec, and because GM is lazy, i'm pretty sure the LS1 computer doesn't do it.
Ah cool thanks, But what about ground clearance? I don't ever plan to lower the car or anything like that, but i can see the flat part of the driver side y-pipe if you look at the car form 20 feet.
I can tell you that the warm-up performance limits for the OBD2 Cat warm-up self tests (the ones that can generate trouble codes P0141 and P0155) are different for the right side and left side cats on a 98 T/A LS1. But I don't know if that is because of the difference in the sizes, or the locations, or both. The bank 1 limit is 407 seconds and the bank 2 limit is 302 seconds. Both are reference to idle speed airflow and are adjusted according to actual cumulative engine speed while the test is being run. The test is designed to detect a failure in the sensor heater, but since the heaters are identical on both sides, the difference in the limits must be elsewhere.
eww you're right, it does check. that's no fun

i guess just move them and hope for the best

ground clearance? that's a different thing altogether. and keep in mind proximity to unshielded floorboard is an issue too, those things can get REALLY hot. i pulled the cat heat shield off a car once, and forgot to put it back on. it turned the carpet brown.
Oh, I forgot to add this: In 2000, the passenger side cat was moved forward and upward in a position similar to the driver side one. Maybe GM discovered something awry with the previous setup.
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