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> For us learners: what is exactly is being compared in a compression ratio? > What's being compressed and what does it all mean? > Compression ratio is a comparison between the volume of air/fuel in cylinder/combustion chamber when the piston is all the way down compared to when it is all the way up. So let's say you have a 1600cc engine with a 7.5:1 compression ratio. Just throwing numbers in here - when your piston is all the way down, at the end of its intake stroke, there is 400cc of fuel/air in the cylinder and 61cc in the combustion chamber of the head, so that's 461cc of fuel/air getting ready for the compression stroke. The piston, which displaces 400cc, comes back up, so now all that fuel/air that was there a sec ago is still there but has been compressed into a volume of only 61cc. So the ratio of volumes from piston down to piston up is 461:61 or roughly 7.5:1. Bring on the spark! Hope that helps. Freddie Lochner http://devoted.to/my69notch 69 Notch 66 Fasty ------------------------------------------------------------------- Unsubscribe? mailto:type3-request@vwtype3.org, Subject: unsubscribe