Supersprint before and after F30 335 N55 dynographs showing the difference between stock and full exhaust with catted downpipe
Some useful information here from Supersprint showing stock versus full exhaust only output numbers on an F30 335xi. Supersprint is using MAHA dyno which is a popular dynamometer in Europe. What is important to pay attention to here is the delta between stock and with exhaust. The F30 335 output with the stock exhaust is measured at 307.1 crank horsepower. With the addition of the Supersprint 100 cell catted downpipe, 80mm pipe, and mufflers, output goes to 318.2 horsepower.
This is a change of roughly 11 horsepower. Not huge but about what one should expect with a catted downpipe and no tune. These numbers would radically change before/after on a tuned car with more exhaust flow but on the stock tune the stock exhaust system does not appear to be a large bottleneck.
Supersprint 100 cell downpipe, 80mm mid-pipe, and mufflers:
Stock versus full exhaust overlay: