The best performing pipe we sell depends on the bike that the pipe is being installed on. Typically, a 2 into 1 pipe will provide the best performance for most applications. If your bike has a multitude of significant engine modifications such as a big bore kit, high compression pistons or a performance Harley cam, then a straight pipe exhaust system may have a slight performance advantage. A shorter pipe will be louder than a long pipe. It is important to remember that a loud pipe does not necessarily mean better performance.