Hello everyone here's a header tube and length calculator to get you in the ballpark... http://www.bgsoflex.com/bestheader.html For those of us running the smaller engines you need to know the cubic inches of your engine ...Also keep in mind exhaust pipe may have a thicker or thinner wall depending on what you're using for your primary tubes so adjust the size accordingly...It's amazing how the length changes with RPMs as well as tube size...Enjoy !!