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Right now, i have the flowmaster flex back system. It is 2in diamter piping. I plan on getting FR Stage 2 cams in the very near future and I am also looking to increast the pipe diamter with a new flex back system.
My question is, should i go with 2 1/4 or 2 1/2 inch pipe? Or, could i stay with the 2in flowmaster setup and not worry about it? Will there be any gain if i switch to the larger diameter? I figured with the stage 2 cams a bigger exhaust will help a little.

I know, on a stock engine, 2 1/4 is better due to back pressure, but since I am adding cams, i was not sure what to do.
 

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2.25 is good for all motor builds. and its not good for "back pressure" its good due to flow velocity.
 

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I'd agree on the 2.25. The Flowmaster uses about a 36 inch section of stock headpipe(after the flex) and could be a bit small. Too bad Flowmaster didn't partcipate in the exhaust shootout since it would have had the smallest pipe diameter tested.
 
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