Hey all,
I was wonderin about the differences between the two. If the car is mostly stock(91 Z w/350) just a home made ram air system and better plugs and wires, would the 3 inch exhaust be overkill? I assume the 3 inch would louder (I plan on using Hooker mufflers) which is fine, but would it hamper instaed of helping? And does dual cats really help more than single? I had an 89 GTA 5.7 with a single cat but my Z-28 has dual. any thoughts?

 

3" exhaust is a good mod for any 305 and 350 thirdgen engine.

The dual cat cars are rated at 10 HP more than the single cat cars, and I believe it. The single cat y-pipe sucks where it joins together.

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West Coast GM Shootout 2001!
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=-

 

2.5 inch is fine if we're talking about a true dual setup. If we're talking about just a single exhaust setup then you will want a 3 incher...

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

 

I've wondered the same. My 1986 came with a factory 2.25" Intermediate. If someone just repalced the cat back, nothing else (mine lasted only 7 years in the salt free South.) Would a 3" not allow ENOUGH backpressure?

2.25 to 3" is a big jump.

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1986 Black/Gold LG4 Z28
Original Owner, 200,000+ near trouble free miles.
Mostly Stock.

1995 Dark Red Metallic Corvette Coupe Original Owner

 

no it wouldent be too much of a step up.
Where did this "not enough back pressure" crap talk come from? Im not blaming you personally Joey1986Z its been on the board forever that backpressure creates more low end. But its not true, the less back pressure in the system the better.

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If you really want to be original slap in a TURBO DIESEL!

 

I'm not knowledgeable enough to give a reliable answer, but after my limited education from this board, I think it has something to do with scavalging.

If no back pressure is needed why not run open headers? Or if noise is an issue, staight pipes to the rear with no mufflers.

You seldom see mufflers on race cars.

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1986 Black/Gold LG4 Z28
Original Owner, 200,000+ near trouble free miles.
Mostly Stock.

1995 Dark Red Metallic Corvette Coupe Original Owner