I plan on using a t3/t04e on my stock GSR and plan on making close to 300hp at 9psi. Thanks.

 

2 1/4" should be just fine for 300whp. Personally I have put out over 400 with 2 1/4" but I will be upgrading to 2 1/2" next season.

 

Thanks. Anyone else wanna chime in? Also, how will spool characteristics change between the 2 sizes?

 

2.25 2.5 at biggest.

Im running 2.25 from turbo to inlet of FMIC, and then 2.5 from outlet to throttle body. This is a popular choice by most people.

When it comes to intercooler piping bigger isnt always better, to big of a piping will hurt spool.

 

I run 2" and it works just fine. No difference from my friends car running 2.25 / 2.5 at the same boost levels. Nothing noticeable as far as lag or power. I just wouldn't go smaller than 2". I say an inch or so bigger than your turbo's outlet. My turbo outlet is like 1.5" ID if i can remember correctly.

 

So for the direction of flow(turbo->IC->throttle body), I should go from small to big or big to small?

 

go small to bigger, or you can keep it consistent. ANother thing to think about when figuring out piping size make sure you knwo what size your intercooler inlet/outlet sizes are. 1) because transition hoses are like $20 a piece,and 2) keep the flow consistent.