OK, I had always thought that all TPI cars came with a 3" cat set-up (except the early 4 bolt cat cars), but my 92 definitely has one 2.25" cat like you'd find on an RS. What's really weird is the exhaust system expands after the cat to what looks like 2 3/4 -3", yet it looks like the stock exhaust.

But i guess my question is this. Can i get a Y pipe from a 3" cat L98 and use that with my stock manifolds? What about aftermarket y-pipes for 3" cats?
...ed

ps. Don't tell me to just get headers. They are a long way off, for now i'm building this car as a pure sleeper.

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Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

I am not familiar with the 82-88 single cat cars, but I know the 89-92 single cat cars use the same exhaust manifolds, and y-pipe. The TPI cars get the bigger cat and i-pipe. You will need a custom y-pipe because the exhaust manifolds are different between L98 and LB9 cars, the L98 cars of these years all have dual cats. You're better off replacing the whole exhaust at once when you get headers. You can do a cat-back and cat now, but save the y-pipe till then.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.25 @ 107.18 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

If I'm not mistaken, yes, its the same size cat and Y-pipe as a TBI car. I know the cat is for certain, and the y-pipe is hideously small as well. When I got my T/A I had what I believe to be what was left of the stock exhaust (it was a mess, it had rotted a ****load) and it was 2 1/4 as well. See if you can find a single cat L98 or G92 LB9 Y-pipe, its most likely bigger than what you have.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

You do have the same exhasut as the TBI, but there is a silver lining to it. To keep the horespower at 200, GM used a smaller exhaust, but the G92, and 350TPI cam. So, you really have a good situation since it is a lot easier to change the exhaust, then to change the cam. If you want to go with the 3" y-pipe, or dual cat setup, then you will need the manifolds that go with it. yours will not work, or go with headers.

89 Transam GTA, a few bolt ons

 

TransamGTA350, do you know if the y-pipe is the same as what the L03s have? What about the manifolds, are they the same size as well? its nice to have someone else besides myself, Glenn91L98GTA, and Pablo acknowledge the fact that there is no peanut cam in the 90-92 305 TPI auto/non G92 5 speed cars.

 

The y-pipe and the manifolds are the same as the L03. The cat and cat-back should also be 2.25" unless an aftermarket cat-back was put on it. Both the 3" y-pipes(4-bolt, and slip-fit), and the dual cat system use the larger outlet manifolds and will only work with those. The LO3 and the 90-92 LB9 A4 use the small y-pipe and the small manifolds. Because of the difference in the angle of the outlet on the passenger side manifold for the small and large outlets, the better y-pipes cannot be used with the small manifolds. They have to be changed together. I've done this and it is a lot of work. Unless you can pick up the manifolds and y-pipe for next to nothing, go with headers.

I have also gotten a lot of criticism for saying the LB9 A4 came with the good cam. It makes sense though.

89 Transam GTA, a few bolt ons

 

**** %#$#*&@^$%*&$#@^, i guess headers are coming in the summer then. I had such high hopes for keeping this a true 'sleeper' with no headers, but i sure as hell ain't putting a set of manifolds back on it. Christ, if i'm gonna put headers on it, i might as well put heads on it too while i'm in there.
thanks for the heads up fellas...ed