Akrapovic Aprilia Shiver Exhaust 2008 - 2009. The Akrapovic SLIP-ON exhaust system is designed for riders who want to upgrade the looks and performance of their bikes at an affordable price, without making a major modification. The Street Legal version of this system officially conforms to all exhaust system noise level regulations for street use.  Measurements of the Akrapovic SLIP-ON system on the APRILA SHIVER 750 (with muffler insert):  Power & Torque: The SLIP-ON system offers a performance increase throughout the entire rpm range. At 9260 rpm we measured 83.7 HP. The situation for the torque curve is similar, with the best results coming in the middle of the range from 3500 rpm to 6000 rpm, where the dropout in the stock curve is filled.