This is the HOT set up in drag racing. This patented award and race-winning vacuum Wave Collector was designed to replace your current open header collector and serves as a power producing merge collector and muffler -- all in a single unit. The technology in this unit results in pulling air through the engine faster which creates more power. When an exhaust valve opens an energy wave is created from the expanding combustion gases. When this wave encounters a lower pressure area such as a larger collector pipe or the atmosphere a reversion wave is reflected back toward the exhaust valve. Borla(r)'s Vacuum Wave Collector Muffler ensures this wave's "anti-node" reaches the exhaust valve at the precise time for its lower pressure to help fill the combustion chamber with a fresh charge and to further extract spent gases from the chamber via a vacuum effect. Made with the same patented award and race winning flow through design as the Standard XR-1 Collector/Muffler. This muffler however is designed for door car applications where a Standard size Collector/Muffler is too large. This muffler is recommended for Full Chassied Cars. Accepted in NHRA IHRA Hot Rod Series Brackets Super Chevy and NSCA. Recommend for high horsepower applications. T-304 Stainless steel will never rust. 100% welded construction for strength. T-304 stainless steel wool for sound control. Best of all it's made in the USA. Just what you'd expect from the world's most experienced (and most winning) exhaust brand.