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      12-01-2011, 12:05 PM   #1
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Downpipes 2 1/2" vs 3"

Any performance argument as to using the Akra 2 1/2" vs others such as the AR which is 3" ? I know there are fitting diameter reductions in the AR 3" as well as other "downstream" reductions (midpipes etc.) but is there any performance difference in using a 3" DP pipe vs a 2 1/2" DP pipe. Opinions?
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      12-01-2011, 12:37 PM   #2
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maybe the other 135 guys can comment on the difference...
i heard some folks say there is a difference (but it isnt big) this is comparing the 3" vs the 2.5" Raceland. Of course Akra is a better product than Raceland.
Would be nice to get a back to back dyno.
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      12-01-2011, 01:19 PM   #3
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I would go with 3"
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      12-01-2011, 09:29 PM   #4
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Comparison dynos done over on E90post show ~5hp difference going from 2.5" to 3", but for the same money why not just get the bigger AR Design DP's.

If you definitely want 2.5" DP's the CP-E ones are an excellent alternative. Essentially the same build and design as the Akra's save for the flex joint, has perfect fitment, and is over $200 less.
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      12-01-2011, 09:32 PM   #5
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id go for 2.5's if i did it again. i would have room to heatwrap them, which i dont on my 3's, they actually touch eachother.
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      12-01-2011, 10:23 PM   #6
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What are you expecting to gain by wrapping after the turbo? I would think keeping the heat in the pipe after the turbo would reduce power due to exhaust gas volume not contracting because of the higher temps? I do understand why you would want to do this before the turbos if you don't mind running the risk of shortining the life of the parts from the increased temps they would normally be exposed to.
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      12-01-2011, 10:27 PM   #7
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Quote:
Originally Posted by scotth944 View Post
What are you expecting to gain by wrapping after the turbo? I would think keeping the heat in the pipe after the turbo would reduce power due to exhaust gas volume not contracting because of the higher temps? I do understand why you would want to do this before the turbos if you don't mind running the risk of shortining the life of the parts from the increased temps they would normally be exposed to.
Reducing the heat in the engine bay? Downpipes go straight to the exhaust, so it just passed to the atmosphere.
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      12-01-2011, 10:40 PM   #8
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It does get warm near the pedels so I see an advantage doing this along that section of pipe for comfort. Not sure the intake temps are going to see any reduction from engine bay temps caused by the exhaust side of the motor if your moving down the road just by doing this?
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      12-01-2011, 11:30 PM   #9
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Originally Posted by sparoz View Post
Reducing the heat in the engine bay?
Bingo!
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      12-02-2011, 12:00 AM   #10
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Wrapping the exhaust helps keep the outgoing gasses hotter and therefore less dens, making it easier for them to get the hell out of the way of the more recently created exhaust gasses being expelled right behind them. Anytime your exhaust cools in the pipe it starts to become more of a restriction. Restrictions are bad.
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      12-03-2011, 11:44 AM   #11
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Quote:
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Wrapping the exhaust helps keep the outgoing gasses hotter and therefore less dens, making it easier for them to get the hell out of the way of the more recently created exhaust gasses being expelled right behind them. Anytime your exhaust cools in the pipe it starts to become more of a restriction. Restrictions are bad.
The energy (temperature) difference pre/post turbine is what drives the turbo to work. Wrapping/coating the exhaust manifold would be beneficial, not so much the downpipe and rest of exhaust.
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