I had the full F1 system on my E90. It sounded like a monster. Words can't describe how it sounds in person.
It was extremely loud when the valves are open and it stinks quite a bit too. Anyway, I spoke to iPE on the low end torque issue. I got a custom build X pipe with 200 cell cats. I could feel the torque improved immediately. It sounded deeper, I would say - 25% in sound volume. The smell pretty much went away. I set the valve unit at 4000 RPM. The only mod I have is the exhaust system. After searching around, I would get the most out of it with a stage 2 tune. Which x pipe would perform better? F1 or my current x pipe? Thanks for any inputs!