Hi, Bob;

What type of engine? If a VW, then yes, there are rings between the cylinder and case that you can vary to adjust the deck height of the piston in the cylinder, determining compression. I have an AeroVee, and when building, we have the option of selecting either 7 or 8:1 ratios.

I built mine assuming that 100LL or the next gen fuel will be available; if not, I can always make some relatively (key word there) simple adjustments. Bear in mind; you'll also have to probably adjust the valve pushrods as well (as in, cut a new set).