The shape of the pipe doesn't matter one way or the other. 2 cycle are designed to run better with a certain ammount of back presure to the engine. The pipe short, long, fat or tall is there to restrict volume. How you restrict the volume is how it effects the reformance of the engine. There are a lot of pipes out there that lay claims to one thing or another that do nothing but restrict air volume and they call it tuned [sm=confused.gif] tuned to a 350 yamaha [sm=lol.gif] word of mouth or experiment yourself is the only way to know for sure if a pipe will work for you [:-]