One of the most popular and cost effective performance upgrades you can make to a Harley-Davidson motorcycle is to replace the stock exhaust with a set of low restriction high performance muffler The stock exhaust pipes and S&S performance muffler makes a great high performance exhaust system with a low price tag The S&S Slip-On muffler will increase the performance of any stock engine This change alone will produce almost eight more horsepower and about five more foot pounds of torque on a stock 88 cubic inch Twin Cam engine Also highly recommended is the S&S performance mufflers for big inch engines because of the excellent low and midrange torque they provide