Depending on the meterial the shaft is made of, changes will vary. My buddy put in a Z1 aluminum 1 piece and got maybe 3 HP out of the deal. Its just beneficial if you're down under the car removing the shaft frequently or if your bearings in the ... uh, middle, saddle thingy(haha, i cant remember what its called lol)... are wearing out quickly due to hard driving. More of a conveniance type of part unless you have BIG power. Its not a bad idea though. I would put one in just because of the above facts.