formulas

[Chris Howard]

<snip>

>Lastly, does anyone have the formula for calculating mechanical 
>efficiency of an engine relating to compression ratio?

I think you mean thermal efficiency not mechanical efficiency:

              1
n   =  1 - -------
 th          k-1
            r

where   n    = efficiency
         th

        k = specific heat ratio = 1.4 @ room temperature        
        r = compression ratio

This formula is for the ideal Otto cycle. Real efficiencies will be lower
than this.

Chris Howard
Mechanical Engineering
University of Sydney
Australia
Email:    choward at extro.ucc.su.OZ.AU
Web:     http://www.usyd.edu.au/~choward/welcome.htm