and yeah, back on topic.... diesels have more compression only because they have huge rods and a much larger stroke than any gasoline engine. but ill leave the math to the people that can do it correctly..
that isnt true. deisels have such high compression ratios because the high piston height and small dish in the pistons creates a 20:1 compression ratio. they use that because the higher compression ratio you have, the (relatively) more effecient engine you run. thats why two engines equally sized, one a deisel, one a gasoline, will get different fuel milages, in favor of the deisel.