3" or 3 1/2" Downpipe? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 6 Old 05-04-2009, 08:28 PM Thread Starter
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3" or 3 1/2" Downpipe?

how much power can a 3" dp support? what is the point where it makes more sense to change to a 3 1/2" dp? I have a ponydown kit with a 70mm precision turbo, looking to make 550-650 hp once I change the heads and get a better block. Car will be a street car with a 5 speed. I got the 3" dp with the ponydown kit, but don't know if I should just make a 3 1/2" pipe and y-pipe and be done with it or what? Can someone help me out?

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post #2 of 6 Old 05-04-2009, 11:19 PM
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i have heard from some good sources that you want a dp 1.25 times the diameter of the exhaust wheel diameter. So a 3.5" would be a good upgrade.

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post #3 of 6 Old 05-04-2009, 11:49 PM
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If you go 3.5" I would section it and use vbands so you can change plusg easier.. the 3.5" is a bitch to get in/out of a fox.
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post #4 of 6 Old 05-05-2009, 08:19 PM
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Must have the sections if you have an ac accumulator. 3.5" is a tiiiiight fit with only 1/4" between trans and k-member.

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post #5 of 6 Old 05-06-2009, 12:00 PM
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i ran a 3" for years w/ a MPT70, i can imagine trying to snake a 3.5" in and out would be tricky

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post #6 of 6 Old 05-06-2009, 12:08 PM
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My 89 vert's BG kit has a 3.5dp.
It is very tight by the firewall/ac accumulator but it fits. No big deal to take off now that I know what sequence to do it in.
It is not sectioned either. Connects to my Y pipe before the trans crossmember. Worst part is that you have to line up the wastegate flange at the same time as the v band on the outlet on the turbo on my kit.

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