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Discussion Starter · #1 ·
I see both sizes for sale. Are there any reasons to choose one diameter over the other?

(for '93 TT w/BPU)
 

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Dont know much about the mkiv, im an mkiii guy. But, bigger is better:D 3.5" downpipe into a 3.5" cat-back will spool realllly fast!
 

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Stinks like sex in here..
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I don't think you need a 3.5 until your pushing 500hp+
 
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Discussion Starter · #4 ·
hey if you have anything with boost--bigger is always better--better yet, take off your exhast and leave it off!!! :rolleyes:
 

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a 3.5 is an overkill. A 2.5" downpipe is good for up to 500hp, above that then you go with a 3". So in reality with a 2.5" DP, that should be enough for a stock twins turbo setup. Also with a 3.5" you will add more wieght to the car and reduce clearance. The 3" as it is already easily hits speedbumps etc. I could imagine a 3.5". If pic does not load click on link below
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"In Corky Bell's book, "Maximum Boost" it is stated that 2.5" exhaust doesn't become a restriction until somewhere between 450 and 500 horsepower (Chart above taken from "Maximum Boost" by Corky Bell). Neither the Toyota CT-26 nor the CT-20b turbochargers can flow enough to achieve those power levels".
http://www.koracing.net/technical/ExhaustSizeChart.jpg[/url
 

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I tried taking that book as the final word but after seeing various exhaust systems show increases when they shouldn't have (according to that chart), I changed my mind. If a 300WHP Turbo Honda is seeing gains by using a 3" exhaust over 2.5" then I can believe a 600 WHP+ Supra see gains using a 3.5" over 3".

Mighty Mouse said:
a 3.5 is an overkill. A 2.5" downpipe is good for up to 500hp, above that then you go with a 3". So in reality with a 2.5" DP, that should be enough for a stock twins turbo setup. Also with a 3.5" you will add more wieght to the car and reduce clearance. The 3" as it is already easily hits speedbumps etc. I could imagine a 3.5". If pic does not load click on link below
"



Full Sized Image


"In Corky Bell's book, "Maximum Boost" it is stated that 2.5" exhaust doesn't become a restriction until somewhere between 450 and 500 horsepower (Chart above taken from "Maximum Boost" by Corky Bell). Neither the Toyota CT-26 nor the CT-20b turbochargers can flow enough to achieve those power levels".
http://www.koracing.net/technical/ExhaustSizeChart.jpg[/url [/B][/QUOTE]
 
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