I have an 88 Iroc 350 tpi and am planning to buy slp 1 3/4" headers this month. I am also planning on getting the new flowmaster dual outlet cat back from summit. I was thinking of getting the dual cat set up, and using the stock cat as well as an identical stock cat(both gutted). I would like to get random techonology cats in the future but cannot afford them now. I know that this is not any where near a bolt . What do you guys think? So far I have an air foil, march pulleys, fpr,ported plenum, msd wires, k&n filters and cut boxes,and a b&m shift kit. I may install an lt-1 in the future. Thanks for your help.
Kory

 

Doesn't anyone have any info on this?
I need to order the headers before the end of the month. Slp has the sale til then.
Thanks for your help.
Kory

 

Are you talking about installing a stock dual-cat y-pipe? If so, then I'd say don't do it. The dual cat y-pipe is restrictive! It uses 2.25" pipes, rough bends, and in some places the pipes are necked down to 2"!

I ditched mine and am currently running an Edelbrock y-pipe, which has two 2.5" pipes going into a 3" collector.

 

I can't tell you exactly how much improvement you'd see... Pontiac says 13% increase in HP in most of its paperwork. I can tell you that my Iroc and my Formula are setup almost identically, the only real differences are SD vs Maf, and single cat vs dual... but the 91 is a much meaner car. My best suggestion if you want to run dual cats, is to get a set of headers designed for dual cats, get two hi flow cats, either 2.25" (stock size) or 3" if it'll fit, and a flowmaster dual cat catback, then have a muffler shop fabricate the missing pieces. The factory pipes from the manifolds to the cats are restrictive as they use crush bends, headers would fix that. The only other way I'd see it as being worthwhile would be if you found a complete setup with new cats. If the cats are old they're probably in need or replacement or gutting.
good luck with whatever you choose.

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Drew
predatorman@hotmail.com
My Website
87 Iroc
91 Formula 14.3 @ 98mph
91 RS Convertible
92 S10
ICON Motorsports

 

Dual 3" cats is too much. I'd say 2.25" cats for a mild 305 or 350, and dual 2.5" cats for a 350 or larger engine. I'm running a 2.5" y-pipe and dual 2.5" cats on my car.

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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=-

 

That pretty much answers my question.
Thanks guys for your help.
Kory