Cool, do some of these engines perform different on the dyno than their stated factory specs. It seems that all of the OS XZB 21 speed tuned engines all have the same HP rating of 2.61 at 34 k. Except my Blue Head XZB ver 2 which according to the info I got with this engine it it was slightly more powerful than the spec two at 130 USDs cheaper. I had an older XZB blue head 21 that ran great for me. I regret selling it but it was part of the deal and then the guy I sold it to blew it up! Thank You Michael