I picked up a RV6 exhaust system today and I'm planning on installing tomorrow. The question I have is, I have an atlp hi flow cat sitting in my garage and was wondering if I could use it along with my stock j-pipe and the rv6 system?

 

yes.
why not?

 

I wasn't sure if the flanges on the stock j-pipe where the same size as an aftermarket one. Will I get a check engine light from swapping the cat

 

No there is no o2 sensors after the third cat

 

deff use the hi flow cat bro.

 

Has anyone just left the rear air dam or whatever it is off the car. It's the black cover under the rear bumper. It looks cooler off cause you can see the whole exhaust.

 

^i believe I read in Inaccurate's diet thread that it does have an intended purpose.
but i'm not sure. I'll do some reading real quick.

 

I searched for the thread but I could only find diet 2.0. Does anyone know about this

 

When I had my WRX I installed a rear diffuser from the STI that looks a lot like the one on the TL. Dont get me wrong, the Subaru one had fins on it; whereas the TL one is relatively smooth. But I do believe it serves the same purpose in that is helps air flow under the car. I was surprised to see it then I installed my aspec kit.