Topic: A112 compression ratio

[zippyfiat]

Can anyone tell me what the compression ratio of a "standard" Abarth A112 1050cc engine is?  According to head combustion chamber info. I have, the CR calculates to around 10.5:1 (without allowing for thickness of head gasket).  10.5:1 sounds too high - that can't be right can it?

Thanks,
Gil

[Pantdino]

Yes, that is correct. I have seen, I believe, 10.4 and 10.6:1 in literature. 
That's partly why they got so much more power out of the engine.

Jim

[Paul vander Heyden]

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