Regular readers will remember that we've done a lot of cool performance upgrades on our buddy Jack's '69 Mustang SportsRoof. Starting on the pavement, we went with BFGoodrich tires on Vintage Wheel Works' Vintage 45 wheels. Baer Brake Systems provided superior binders for Jack's car, while Auto Krafters parts have completely refurbished his suspension. Under the hood, Air Flow Research and Comp Cams products have seriously helped the 351 Windsor engine. A set of Hooker Super Comp headers was worth over 18 hp when we started the engine upgrades, but the passenger-car-type mufflers and 21/4-inch pipes remained in place.
When we left off on the engine modifications, Jack's car was making 277.3 hp at the rear wheels on Superior Automotive's dyno jet. We wanted to revisit the exhaust system to see if we could improve the engine's power output even more. The exhaust technology experts at Flowmaster suggested a pair of their 40 Series Street Mufflers--featuring Delta Flow technology--along with some 21/2-inch tailpipes. By going to these mufflers and the larger tube diameter throughout the system, we're confident we'll gain power. We wanted to know how much, so we made an appointment at Superior Automotive to dyno-test the car once the new exhaust system was in place.