To be able to calculate it, you need to know (the builder should have measured during assembly and written these down)
1) combustion chamber volume (Stock head is around 55cc? I think)
2) distance from piston top to cylinder top at top dead center (somewhere around 1,5mm is common I guess)
3) stroke (Stock stroke is 69mm, and that's what you have)
4) bore (yours is 94mm with that engine size)
#1 and #2 are critical, no guesswork accepted. Values I gave are there only to give you an idea of what ballpark the values usually are in.
one very important "spec" you left out was what kind of distributor you have installed...Jan's answer will get you there, but it is kind of a "one size fits all" type thing...as he said compression ratio would be nice to know as would fuel quality and octane that is available to you...
------------------- Chris Perdue
*All opinions are those of the author of this post* "Sometimes you're the windshield, sometimes you're the bug"
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