i currently have a 2001 a4 1.8t. apr stage 1, k04,carbonio intake, buying a test-pipe. i am wondering if the 2.5 flange will fit on my stock down pipe and what kind of gain/noise will i notice after install. any other mods you would suggest? other than the obvious full exhaust

 

it should work, you will notice more groan and lower end tq

as for more mods, maybe a proper tune?

 

Turbo kraut- what do you mean by a proper tune? Do you mean for him to reflag his Ecu and get the stage 2 tune? I'm curious as well.

 

I mean reflash/upgrade what needs to be upgraded to take advantage of the turbo. Right now he's getting ko3 power

 

Im noticing faster turbo response and higher psi (gauge spikes to 25 and steadies around 15-20) i can deffinitly tell a diffrence in my car with the k04

 

OP, the 2.5" flange will fit fine. I'm running a 3" ATP test pipe and it fits wonderfully. You'll definitely hear the turbo more, and it should gain you some higher torque numbers and quicker spool. Make sure you use new gaskets, and you're going to want a spacer for the rear O2 sensor.

Have you upgraded your diverter valve yet? Spiking 25psi with a K04 on the stock DV will trash it in short order.

 

The cat works as a muffler also. Removing it will increase noise and flow. A full turbo back will reduce it further and also remove some weight from the car