like my buddy has a 84mm bore and a 64.5 stroke and he wants to know how many cc's it is and i dont know what formula u use to get it

i thought it was just bore times Stroke

Should be radius of the bore squared, times 3.14, times the stroke, and then divide by 1000 to get cc's. Your buddy has around 357 cc's.

I forgot, for multiple cylinder motors, multiply that number by the number of cylinders.

ok on the compression like 10:75:1

what does each numeric value represent

10 75 1 ???

Compression ratio is how much space in in the cylinder at the bottom of the stroke compare to amount of space when it is at the top

Its 10.75:1

10.75:1

ok for an example

at the bottom of a stroke you can give it a value of space being 10.75
and at the top you can give it a valve of space being 1

the numbers represent the amount of space, but what are the numbers 10.75psi 10.75mm 10.75cc 10.75in ??????? 1mm 1cc 1psi????

At the bottom of the stoke you would have 357cc and the top you would have 33cc

or it compresses the fuel/air mixture 10.75 times