Im trying to learn about engines and Im sorta stuck. What does it mean 10:1 10:5......for a 103 or 107 what is a good compression ....

 

10:1 means the total volume of the cyclinder and combustion chamber is 10 times the volume of just the combustion chamber. When the piston rises from BDC it squeezes that 10X volume up into the 1X volume combustion chamber. I think the 10:5 is a typo for 10.5:1, the same still applies. 103" or 107" doesn't matter, displacement does not dictate the compression requirement, the cam does.

 

It was a typo. So 10:5:1 means it requires more for lack of better words power or force........

Also on cams, the size of the lift is what determines the compression ....is that right or.....

 

Not sure what your trying to say, just put 10.5 in place of 10 in my original explanation.

Negatve Bro. Valve timing is what dictates compression. Sorry I'm not really qualified to explain camshafts to you, start researching cams. If I try to put this in laymans terms I'll have all kinds of folks playing the symanics game and correcting my explanation.

 

ok thanks for the information .....it helped me out alot ..... understand the laymens terms.....my friends are like that also

 

I think part of the confusion is compression ratio and cranking compression. Compression ratio is the Top dead center volume divided by the sweep volume. This gives you a ratio such as 10 to 1 or 10.5 to 1 or 9.5 to 1. Using the : to separate is confusing. The cranking compression is definitely a function of valve timing. Cranking compression is measured with a compression gauge and has very little to do with compression ratio. The later the intake valve closes after Bottom dead center of the piston the lower the cranking compression will be.