900ss with factory pistons. I have 10.8:1 pistons in my 900ss, needs 91 or higher octane or else.. high comp pistons were a common upgrade on the carby bikes. At 11:47 PM 7/19/2007, you wrote: >So you'll get the most power with the lower octane if you can run >it, and a 900ss has a pretty low compression ration. > >marko