This high performance muffler has been developed for vehicles with 4" sidepipes such as 1965-74 Corvettes or vehicles equipped with Hooker Super Competition Roadster and Side Mount Headers. These mufflers produce an average of 23% more power than open headers and feature a high-flow, perforated core that operates at 99% efficiency. High temperature packing material absorbs noise while producing a powerful mellow sound. These mufflers, as tested on a 1968 Corvette with a 427 cu inch engine increased horsepower by 40 at a peak of 5500 RPM and 20 ft.-lbs. at peak of 4500RPM versus a leading aftermarket undercar header/turbo-style muffler combination. The outer case is constructed of durable 16 gauge aluminized steel protected by electrostatically applied high-temperature black paint. The inlet/outlet is a 2.5 perforated core in a 4" casing. Sold in pairs.