Can somebody explain to me what a compression is and what those numbers mean ex. 13:1? i dnt know much yet and i tried searching it on HT and i cant really find an answer to my question. Thnks

 

http://auto.howstuffworks.com/engine1.htm

That site has alot of other usefull info as well, and its all broken down
To learn what compression is i highly advise you to learn the 4 stroke cycle of intake, compression, power, and exhaust

 

In the animation above you will see the piston travle from the bottom to the top of the cylinder. lets say our engine has 1.6L now we divide that by 4 cylinders, and we get about 400cc per cylinder(keep in mind that this is the volume available in the cylinder at whats called Bottom dead center, the bottom of the pistons travel)... now if you were to measure out the volume available in whats called the combustion chamber, at the top of the cylinder( or Top dead center). you will get a compression figure.
400cc per cyl
lets say 9:1 compression ration... now whats 1/9 of 400?
400\9= 44.444
so the combustion chamber size is roughly 44.444cc of volume
and the piston has squeezed the air fuel mixture down to 1/9 of its original size since it was drawn in at the intake stroke

 

thnks...that was a good site has a lot of info....

 

good link very helpful