Eurotuner Magazine has tested the following cat-backs....AFE = No gain; BMW M Performance = +2-3 hp avg (+5 hp on best run); and Gruppe M titanium +3 hp avg (+5 hp best run). In addition to hp gains, area under the curve in both hp and tq was slightly better at 2-3.5k RPMs.
Originally Posted by pbonsalb
I'd like to see dyno results since claims vary widely. BMW claims no gains for its performance rear exhaust, AA claims around 10 hp, someone reported that Eisenmann Race was worth 15 rwhp, and Akra claims something like 3 rwhp, but I don't think I have seen any dyno tests.