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Old 12-15-2008, 11:35 AM   #1
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Default Custom downpipe sizing

I am planning on having TurboTony make me a custom downpipe for my CarTech/IHI setup. My question is what size should I pick. Is there some sort of formula for pipe size, is there a relationship between the output hole in the turbo housing and the downpipe diameter. Should they be equal? Larger? Can it be to big?

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Graham
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Old 12-15-2008, 11:43 AM   #2
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I go by the idea that Bigger is Better on turbo setups.

Not sure how far you are from South Holland, IL... but I have a buddy down there that can make you a custom DP also. He did the fabwork on my setup.
Does TT have the stuff templated for your specific setup?
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Old 12-15-2008, 11:46 AM   #3
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TT does not have a template, so I am planning on shipping him my current downpipe. The current one uses the stock mid pipe, so it must be very restrictive.

Fastg
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Old 12-15-2008, 11:53 AM   #4
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Easy enough, if you do want to keep it local and have it done to exact fitment with no questions the first try... I can pass you onto my friend. Does great work for great prices.

And for size... I like 3" as the ideal fit/cost compromise.
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Old 12-15-2008, 12:05 PM   #5
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This is a real small turbo, do you think 3" is worth the extra cost of the rest of the system. I was thinking 2.5"

Sure send me your guys info.

Fastg
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Old 12-15-2008, 09:46 PM   #6
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Quote:
Originally Posted by FastG View Post
This is a real small turbo, do you think 3" is worth the extra cost of the rest of the system. I was thinking 2.5"

Sure send me your guys info.

Fastg
yes.

start with turbine outlet size and then step up to 3" as soon as you can. the exhaust gasses are still expanding as they are enter the downpipe so give them some room.
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Old 12-15-2008, 09:57 PM   #7
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The small outlet on the IHI turbo is just 2" so is it still important to go with 3"?

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Old 12-15-2008, 10:13 PM   #8
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the actual outlet of my 16g is also only about 2" as well and yes it makes a difference. most notably in spool time. I also picked up about 20 free hp by switching to a 3" exhaust after the dp. although it may be diffucult to get to 3" at the flange it does have some benifit to go big as soon as you can. it's not a must but it is better.
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Old 01-13-2009, 10:14 AM   #9
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I went w/ a 2.5" DP (same for rest of exhaust) for my 16g, couldn't tell you if 3" is superior, but it was tricky enough getting a 2.5" pipe routed. I'd do it again, I'm hitting 12psi pretty quick.
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Old 01-13-2009, 10:52 AM   #10
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Dont bother with 3 inch. On a setup like yours its just extra money and headache.
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