9.8-1 is safe with a adjustable ignition and fuel set right on 93 octane, 9.5-1 is a goal if good gas is a problem with a EV27. Running a Woods that is comparable to the EV27 except has high lift and have no problems with 9.8-1. earlier the cam intake closing, the lower the compression should be set at, that is why the EV13 is recommended 9.25-1 and EV27 is 9.5-1, early intake closing cams are compression builders.

 

10/1, ev27 is plane awsome set up. Tried and true for many years without over killing the engine.