Exhaust Port Torque Cones for Harley-Davidson Big Twins and Sportsters EXHAUST PORT TORQUE CONES FOR BIG TWINS AND SPORTSTERS.Improves power by increasing the exhaust gas velocity. Helps to reduce exhaust reversion. Simple installation requiring no permanent modification. Great for use with unbaffled exhaust that require some type of back pressure to run right. Precise angles for maximum effect. Extra exhaust port gaskets are not required. Fits all Harley-Davidson Evolution models, all years and Twin Cam 1999-LaterGreat for any custom chopper. Why use torque cones? Exiting exhaust gasses are sometimes pulled back into the engine by descending piston before exhaust valve gets a chance to close. Exhaust gases in the cylinder contaminate the mixture of fuel and clean air and significantly reduce engines performance. Torque cones are commonly use