The FVD website says the Sound Version adds 11 hp to the crank. So that would be less to the wheels. I believe SpeedArt says 11 hp to the wheels. Remus says up to 21 hp, but they don't say whether that's to the crank or wheels. Either way, shouldn't the Remus make more power? I like the way both the Remus and the SpeedArt sound. I haven't really heard the FVD. I'd like good sound while still gettin' as much power as I can. I really like the Capristo a lot, but it's a little outta my price range at the moment.
I hear the speedart (and perhaps FVD) have been accused of underpromising and over delivering....independent testing was pulling around 20HP crank. Remus prefers to claim % increase VS a flat number since your existing mods will make a difference and a base and S version car will not show the same increase. The numbers on Borla and Remus are crank and you should see high teens at the wheels when accounting for driveline loss.
Of course every car is a little different depending on how the car was broken in, mileage, type of fuel, how dirty is your air filter, temp/humidity, engine variation, etc...so your mileage will vary when it comes to reporting numbers (not to mention Dyno testing has a range for error depending on the tester and conditions).
Vids of an FVD system on a cayman can be found on 6speed.
