For starters i have a J2 Engineering dual exhaust on my 2012 GSR with a aftermarket down pipe and shortram intake. The car has been tuned and is running 400hp to the wheels. My question is if i was going to run a strait pipe fron the axle back would I need a retune or would i be ok?

 

nah

 

Axle back wont change a thing on your tune.

 

You will not need a tune. If you swap you cat for a test pipe or a high flow cat then you will need a re-tune.

 

400 HP with just intake and exhaust huh?

 

I just caught this in his original post. There is no way he's making 400whp with just an intake and a exhaust. I made 406whp/411wtq on an Evo X with a stock turbo, E85, and every single bolt on power mod you can put on this car. On crappy Arizona 91 it made 362whp/362wtq.