I'm not 100% sure on that one, your best bet would be to PM bradtyler for the details, or call RAI directly and ask them

LOL i'm not cheezus i swear, just trying to help out another AF member

 

I already had a 2.5 inch cat back installed before I got my test pipe, so I don't know if the test pipe will bolt right up to stock or not. What I can tell you is that I couldn't find a gasket that fit right, so I had to use copper spray on gasket in a rattle can... been installed for about 9 months now without an issue...

As for HP gains, I think it's negligable... The turbo spools a couple RPM soon, that's about it.

 

Yea, most of them claim 10-15 hp but its probably closer to 5 with a stock setup. Obviously the gains seen with mods will always be better with a test pipe vs a cat. The main benefit is for an overall more responsive torque band that will also allow the turbo to spool up to pressure a couple-hundred rpms sooner. Horsepower gains will be in the upper rpms at wide open throttle.

Edited OP with info comparing all the test pipes

 

Ok so, in the future im gonna go 2.5" back from the cat to a muffler.
From a shop nearby.

But I'm a little bit confused as to how much of a pain this is gonna be to install on my stock exhaust?
Im planning on buying the ecs pipe, but its looking like ill need 3" exhaust....
Not to sure.

 

There's no definite answer, it depends on a lot of things and how much you're worried about your "flow". What you're trying to avoid for example is bolting up a 3" test pipe directly to a 2.25" down pipe without any type of reduction. The bolts may line up on the flanges but you're cross sectional area is reduced by 44%. Not only does this flow less to begin with, but it also creates turbulence which disrupts flow even more.

If your going with the ECS test pipe its a 3" inlet and outlet. The inlet is perfect as the exhaust from the turbo is just a hair under 3" I believe. When the shop builds your exhaust you're gonna want them to bend a down pipe that goes from 3" to 2.5" then you're all set from there. If you're planning on running a stock setup or lightly modified (K04 and GIAC) you can probably not worry about the down pipe to save cash. I think the OEM down pipe is less than 2.25" (2.125 ID maybe?), but you can use an adapter that goes inside the pipes to reduce from 3" to whatever you need. This will decrease the turbulence in the transition. The smaller down pipe is negligible with a stock or K04'd engine. If you're planning on staying stock and just want an exhaust with a better tone you can even keep the 2.25" exhaust and have the shop replace the resonator with straight pipe then put an aftermarket muffler on, it will be more than enough flow. For light modification I'd go with 2.5" exhaust and a replacing the down pipe will squeeze a little more torque out of the bottom end and power in the upper rpms.