Yes, 10.5:1 is the published compression ratio for theA112 1050cc - 70HP motor. Given the cam specifications for duration and lobe center for the standard cam, the Effective Compression Ratio is 8.65:1. This would indicate that the motor would run quite nicely on 95 octane fuel. The horsepower curve shows increases in HP up to about 6500-6700 RPM, and then the power drops off.
The effective compression ratio is calculated by determining the position of the the piston in the bore at the actual time that the intake valve closes. As with most engines this event is "after" BDC, thus the total volume available for compression becomes less. This is one of the keys to making horsepower, namely determining what is the optimum combination of camshaft duration, lobe center and effective compression ratio.
Paul Vanderheijden
www.scuderiatopolino.com