ek9 system is fantastic, you dont need to upgrade on stock car and MASSIVE bonus of being quiet so hear engine rather than exhaust
I agree with this, with the less restrictive exhausts fuel usuage goes up a fair bit, torque is decreased and it only feels faster because of the noise. Only really works changing the system with a mappable ECU. In my experience anyway.
so would a plug and play ecu not pick up on a less restrictive system?