Originally Posted by nicknaz
Other than switching the downpipe, do you think there are power gains from the exhaust?
Or to ask it another way, if someone wanted the "stage 2" power with OEM sound, this is possible by changing the downpipe and keeping the OEM cat back exhaust, or are there bottlenecks in the airflow with the OEM exhaust?
Cobb Stage 2 OTS Tune does not require a cat back exhaust mod. it will work with DP, FMIC, DCI as only mods.
with the exception of 135i. they tested to see that 135i's stock exhaust was too restricting.
My thought is that Cat backs are mostly for sounds, with minimal performance gains.