Topic: Yoshimura 812cc big bore

[rokhedjo]

Any idea what the compression ratio was on the Yosh 812 big bore kit was?

[754]

Got a pic of the piston ?

[PeWe]

Probably made for stock chambers, around 22.5cc.
Compression make power, not too much though.

My bike became happier when my cheap compression tester showed 200PSI instead of earlier 170-190 area with different cams with my old head.

Last head with smaller chambers popped up the dyno chart.
Previous head had even 5mm stemmed valves and ported more.

[Jerry Rxman Griffin aka MuthaF'er]

Mine is likely 10.25:1 or 10.5:1. It is NOT 12.5:1. Works fine with stock head and Yoshi Daytona cam and HD springs.