You're rpms will depend on how you build the moter,However the 10 and 11 horse moters(25 cid) use the same piston and rod as the 12 and 12.5 hp (28 cid) but have a differant (shorter) stroke and shorter deck height, I noticed the 11hp moters reving up higher than than the 12s, and the couple of guys running them have been doing so sucsesfuly stock against mildy modified 12s. (at least at are 1/8th mile oval antway)One particular fellow has used a stock 11 as his back up,and seemed to think it was quiker.Ive always been told these moters are the same,So we always blew him off thinking he was pulling are leg about what moter he'd run.But know that I checked it out myself I can tell you theres almost a 1/4 inch diff in stroke and deck. Now that I know what if seen and found out, I think when I can, Ill build me an idintical 11hp as my 12hp and try it out. If anyone has tried this or has any input on this,Im starving for input.P/S This means you goerge. tb