compression from hot to cold

[BURKE_DADDY]

just wondering in general how much compression would differ from hot to cold.ie checking it cold and then checking it when the bike has warmed up?

 

thanks for the help

[wesw]

you will have more compression when your motor is cold cause the parts havent heated up and expanded a bit.

 

dont know how much of a difference there is between cold and hot.

[BURKE_DADDY]

you will have more compression when your motor is cold cause the parts havent heated up and expanded  a bit. 

 

dont know how much of a difference there is between cold and hot.

341665[/snapback]

 

sorry for the late reply but i forgot to track the topic didnt know anyone replyed.

 

wouldnt the compression be higher if the engine was warm?

[J-Madd]

sorry for the late reply but i forgot to track the topic

Edited April 29, 2005 by J-Madd

[RNBRAD]

You could calculate the pressure of a specific volume of air at different temperatures using an equation that I forgot loooooonnnnnggg ago. But, I do know that warmer air has a greater pressure, as the molecules are moving faster.

 

Ideal Gas Law PV=NRT. Only thing I remembered from chemistry.

 

There would be no way to accurately measure the change in compression from hot to cold, though it would change, but I'm not sure how much the air expands once inside the combustion chamber. It's in there for such a short period of time (with engine running)and you would have to calculate it's rise in temperature just before combustion would normally take placed compared to the ambient temp. Too many variables and no way of testing it accurately though theoretically it happens.