Hi Ace, If our machines are anything to go by, our 500 can pull 125 mph at peak power rpm on the dyno [46 bhp] with the highest gearing we run [and also reaches these rpm's and more on the track], peak power is around 6,200 rpm. BUT ... racing gearing will be different to a speed record attempt gearing and our gearing varies from track to track and is usually lower than the above, two circuits excepted. 37 bhp from the 350 gives 114 mph, so I would guess that 40 bhp should be enough for a light machine with good streamlining. I could count sprocket teeth tomorrow if it might help, but you know as well as I that you will want pretty tall gearing. Also Avon race tyres put around 2bhp more to the ground than the equivalent Dunlops, although 'Henchy' prefers the Dunlops for his cornering style. What I mean is research your tyres and their sizes, the right choice might be the 'clincher'. Good luck ! B.W.