I used to have a BH001 HKS exhaust system on my Honda Civic Si, but decided to replace the system with an Aero Performance Exhaust 2540i along with Aero´s Stealth 194. My car instantly gained torque off the line and even added fuel economy, but the best part is that my Civic's sound went from a whining high pitch to a low mellow deep tone with the Aero Performance Exhaust system. My Civic Si now sounds like a monster. This muffler is awesome! This is the best performance import exhaust out there.