3 inch catback vs 2.5 inch catback
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From: Florida
3 inch catback vs 2.5 inch catback
I just received my LG pro motorsport long tube headers, and was inspecting them and saw that the pipes are 3 inches thick and my corsa indys are 2.5 inches. So my question is how much if any hp would I gain if any from going to a 3 inch catback, like the GHLs. What is the stock midpipes and stock catback sizes? Just thought I would throw it out there since it seems that going from 3-2.5 may cause the exhaust to be turbulent.
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St. Jude Donor '07-'08,-'13-'14, '16-'17
2 3/4"...no gain unless you are pushing a lot of air...more than just headers...
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Last edited by CCA Corvette Parts; Jan 24, 2006 at 08:04 PM.
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From: Bartlett IL
The exhaust cools as it moves rearword, so takes up less space (volume). 1500* or so up front and 200-300* out back. Cool contracts, heat expands. so the optimal size for the rear is 2.5 since the exhaust has less volume. If your worried about turblance have a welder install a 3" to 2.5" reducer cone. 
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From: Bartlett IL
By cat back do you mean the mid secton or the rear muffler section? I believe all mid sections that use stock cats are 2.5". As far as 3" muffler section, I couldn't see you loosing power. But you probaly won't gain much eather. Unless its a large cid motor of forced induction. As far as a 3" mid section, its "usally" worth 5-10hp depending on the car.
