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2001 2.5RS Aspen white
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98 Posts
Discussion Starter #1
Ej205 motor with 250hp soon to reach 300whp.

What are the pros and cons between the two sizes and which is ideal?

Preferably, i would like a 2.5in, for less weight, and "supposedly' slightly faster spool times as well as a quieter sound.

Any input?
 

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93 Legacy
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1,355 Posts
Not gonna matter too much weightwise, 3 inch is good. Ive ran both full 3 inch an 3 inch to 2.5 out at muffler tip currently. I prefer the latter since there is close to zero lag. 2 cents.
 

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'04 PSM WRX Premium
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8,339 Posts
Most people are going to run 3" on turbo applications. Think of like Cobb's etc... time and money went into R&D to select that size.

Second, if you're approaching 300WHP, that's roughtly 350 or more crank HP. I'd consider the extra airflow you'd need at that level.

Most basic stage 2 setups are 3" and have little spool time on the stock turbo. Spool has more to do with the turbo itself. What are you running?
 

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99WhiteMock22B/10TeslaRoadster
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6,659 Posts
I have never really seen anyone trying to push the 300whp mark with a 2.5 because at that point you are trying to get as much flow as possible. The weight will be basically negligible also.

If you are trying for a quiter TBE, there are a few out there. Borla Hush, MRT, Cobb...etc. Just youtube videos and there are plenty of them showing the noise or lack there of all over. Good luck to 300whp!
 

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2001 2.5RS Aspen white
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98 Posts
Discussion Starter #5
thanks for the input guys. I have always ran 3" exhausts on my turbo cars but they had more whp.

I'm all about custom exhausts, so those brands are out of the question! lol.

at the 300whp level I plan on using an evoIII 16g.

But given the input here and some thorough research. I think 3in will be the way to go.
 

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I like to run stock size from headers to turbo (to retain the quick spooling capability), then 3" from turbo back.

I have heard that increasing the diameter of the up pipe has a negative effect on spooling. I have not confirmed this with my own experiments, but makes logical sense (the Bernoulli effect).
 
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