Designed for hard tuned, street driven vehicles, the ps revolution's exhaust pressure activated "active valve" system provides the hardcore enthusiast with the best of both worlds. the retracting valve is engaged and disengaged based upon exhaust gas pressure. this revolutionary new muffler design allows high powered street cars to maintain a tolerable, and legal, exhaust note at idle and light throttle acceleration while completely disengaging during high throttle, high load situations.