The DynoMax Ultra Flo converter-back exhaust system (PN 19434) from DynoMax [(734) 384-7806; www.dynomax.com] posted a gain of 17 hp and 13 lb-ft of torque at 5,400 rpm in recent dyno testing by DynoMax. Designed for the V-6, this is one of a handful of true dual exhaust systems on the market for the 4.0L. DynoMax’s Ultra Flo after-cat system for GTs, Shelby GTs, and GT500s (PN 19414) includes 3-inch mandrel-bent piping and polished tips. DynoMax’s testing showed gains of 11 hp and 15 lb-ft of torque. If you prefer, this system is offered with a pair of Bullet mufflers.