It could have been me. When I took my car to the strip (1/4 mile) I only had a modified airbox. I ran it with the muffler and without and there was no difference in time. Thing is, the ECU could not compensate for the extra flow so if I would have allowed time for the ECU to learn, then my times should have been faster. I then installed a flowmaster type muffler and the car was SUPER loud even with the resonators in place.

I would highly recommend against a Flowmaster. It might sound great on a V8 but not on our cars. I removed it after a week and went with a stock WRX muffler which gave me better top end and even got rid of the rattling in the engine at high RPMS.