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Mag 10 has 904 12:1 racing pistons on his profile, his two cents on the subject would be interesting to hear. My experience with Octane issues have been associated with car engines and as their exhausts are usually configured different from bikes, you can hear the pinging/pre detonation sounds a lot easier. I currently own a 300H.P. Alfa R. that craves 96 Octane min., so I feed it the best gas I can find and add a $10 a bottle stuff to every tankful to bump up the O. level.



Here is my 2 cents (adjusted for inflation - zero) the setup with the 12:1 s kicks a$$. That said fuel is a problem. It wasn't so much of an issue when I built the motor but it is now. It really runs best on 98 octane. On my way to work there is a track and the gas station nearest has 115 and sometimes I will blend it with 91 or 93. The higher % ethanol fuels seem to do better without knocking.
If you do go with the higher compression motor I would strongly consider retarding the timing. I have 8.25 degrees retarded on the pickup head and 3 more in the procom at the bottom end. With that it will be okay on 93 with ethanol.

05 speedmaster - 1100cc, 11:1 racing pistons, Carillo rods, thunderbike cams, ported and polished head, 2mm over intake and exhaust valves, Barnett kevlar clutch, scepter pipes, oversize manifolds, 45mm HSR's, TTP stage 4 firestarter