24F0 Hayabusa, 6#, 3 hole flange: I was very relunctant to exchange my 40F0 for the slightly heavier/longer 24F0, but Jesse highly suggested it, and he was dead on the money. Initially I missed the "thump" at idle that I had became accustomed to, but became more impressed with each run up and down the road, a lot smoother than the 40, more like the stock except much throatier with out the restriction. In the highly unofficial seat-of-the-pants test, there was no comparison; my DR ran like a scalded dog, except for it felt much more refined, if a scalded dog can seem refined. Jesse also included a very trick spark arrestor; never been checked here in Arkansas, but still looks cool as all get out, so that counts for something. In the spirit of full disclosure, the other bikes were running stock headers, whereas mine had the FMF... volume levels were very similar to the 40F0, but a lot smoother.