I'm building a 385 for the Iroc. SLP headers seem to be the best, and the most emissions compliant, but I don't like the 2.5 inch y-pipe on the single cat setups. I'm thinking of going with the dual cat ones for better flow, but my question is, what is the diameter of the y-pipe on the dual cat setups. Thanks for the help.

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'89 Camaro RS 6cyl. auto, don't know how much longer I'll have it.
'90 Iroc TPI 305, 5 spd B&M Ripper shifter, hopefully I can rob a bank or something and get more
www.geocities.com/irocnroll90

 

slp's y-pipe puts 2 2 1/2's into a 3 on a dual cat system. i just put a set of SLP 1 3/4 headers on an '89 GTA, and are familiar with all of the problems you may run into. Feel free to email me with any questions at www.hipergp@aol.com. I'd be glad to guide you through the installation.

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'84 Berlinetta, LG4, 700R-4, starwars interior, no major mods yet

 

Well there really isn't a true y-pipe with the dual cat version. What you get is pipes that lead all the way to the cats. They are either 2.25 or 2.5 inch. From the Cats back the stock pipe ends up being 3 inches.

With the type of setup you have I'd say go with the dual cats. 2 will flow better than one, but that's my opinion.

Hope that helps!!

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'91 Z-28 5.7, SLP 1 3/4 headers, 4 inch Mufflex/Flowmaster cat back, gutted cats, Edelbrock intake, 8.5mm Jacob wires, MSD Blaster coil, S&W subframe setup, Jacob Pro Street Ignition, complete Kenwood system.

 

I'd say slowv8berlinetta would have some experience.. he's the dude who helped put those puppies on my baby. Anyway, go with the dual cat setup, stock it flowed 15 horsepower better than the single cat setup, so if you add headers it will obviously add up that much more.

Jon


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89 GTA
Beautiful Gunmetal gray, LB9 305 and T5 tranny. Only 60,000 miles!
Dual cats, 3"flomaster
Accel 300+ Ignition, wires, cap, coil, etc
Airfoil
KN Airfilter
Removed Screens on MAF
SLP 1 3/4 headers
No Smog/AIR system

 

Stock dual cats was worth 10 horsepower over a single cat, at least according to GM's ratings. Mostly its because the y-pipe is a better design than the single cat version.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

I ran without a cat for a few days after I installed my SLP headers & exhaust, when I decided to comly with our government, I think with the cat I had a little more power.

Did not make any sence to me whatsoever.

From what I understand, the new cats are better than they were back ten years ago. I was going to do what you are thinking of doing with the dual cats, until I learned that for safty reasons you should get the 1LE heat shield for under your car where the cats go (unless you eliminate the cats).

Just a few thoughts

John

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87 Formula Yellow/Black

5.1 TPI Automatic
Baer 12" brakes 4 wheels, KYB AGX Adjustable Shocks & struts, Custom Leather interior, WAAAY TOO MANY MODS TO LIST

87 Formula TPI (5 Speed) Yellow/Gray STOCK

1967 Buick Riviera 430hp Turns high 14's (Not bad for 4300 lbs)

83 Camaro (Parts)
83 T/A (parts)

http://www.3rdgenformula.com

[This message has been edited by okfoz (edited September 03, 2001).]

 

Thanks for the tip. I'd run only one cat, but SLP's y-pipe exits at 2.5" which makes no sense to me, that's why I want two pipes of either 2.25 or 2.5 whatever it is, I'm still not exactly sure and hoping somone will help.



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'89 Camaro RS 6cyl. auto, don't know how much longer I'll have it.
'90 Iroc TPI 305, 5 spd B&M Ripper shifter, hopefully I can rob a bank or something and get more
www.geocities.com/irocnroll90

 

Your car probably seemed like it had more power because running the car you car will actually make more torque on the dyno, but will make less upper rpm HP.



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Jason "TrickFlow" Zajac

JnJSpdShop@aol.com