Since I'm still in the rebuilding stages, I have been doing a lot of reading. I am currently running 2 1/8" primary tubes into 3 1/2" collectors. I am going to build up another set of 4" collectors for testing, since the new motor is 500". I have been thinking about trying out some merge collectors. Maybe narrow down to 3" and come back up to 4" or 4 1/2"? Has anyone seen any real improvements over a standard type collector? From what I have read, bottom end torque really increases without sacrificing top end hp.