any one got any info on length of pipe from headers to the end of exhaust for best performance on straight threw pipes in 3inch twin system for 409 clevo

I remember reading a good tip in Hot Rod magazine a few years ago that seems to work - start with a fairly long length of pipe, draw along it with a grease pencil or paint and pull a run - where it gets hottest, i.e where the grease pencil or paint burns off first, should be the hottest and therefore optimal point at which to cut the pipe... we tried this years ago on an old stock car we ran and it seemed to help torque....

thanx mate that sounds like it could be a good starting point