Ok, so I got an APR chip for my 1999 B5 Audi A4 1.8t a few weeks ago... Great improvement to performance btw...
Now I'm thinking about getting a Borla cat back exhaust system. My friend says that will mess with the chip and that I'd have to get it reflashed after I get the exhaust system. I'm inclined to disagree with him because logically that would mean I'd have to get it reflashed after every single engine upgrade/change, but I'm not 100% sure so I thought I'd ask if that was true or not.
You do not need to get it reflashed, but if you switch to the bigger injectors you need to get the stage II tune, which is free if you would order your injectors from APR or an APR dealer, I have the APR Stage II kit with the APR exhaust, and my car is alot faster than it was stock. Will take it to the dyno in the next couple of days.
Alright, so I should be fine then... I'm not going to get bigger injectors for a while, first I'm going to get the Borla exhaust and then probably find a cold air intake. Thanks!
I would go with bigger injectors before I got the cold air intake. The CAI does not make a great gain on performance with these cars, the stock air box is plenty sufficient with the little bit of mods that you and I have, injectors will make a much bigger difference than a CAI. APR reflashes your chip (ECU) for free when you get the injectors too.
Printable Version
Catback with APR chip? - 
