[eod_blaster]

Need a lesson on compression ratio terminology. Ultimate question is when someone says a cam works at XX.X C/R, what are they talking about - CALCULATED or CORRECTED ??? Also, what is and where does STATIC C/R come into play????? thanks for any help

 

[HIPPO]

Normally when one mentions that a specific cam will work best @ XX CR, one is referring to the calculated static CR.

Once you get into dynamic CR the cam specs come into play, ie you can play the cam specs against the static CR to achieve a specific cold cranking pressure at a given altitude.

In it's simplest terms, once you get past that you have to figure VE and a few other things to figure BMEP, but that's beyond the scope of a forum.

 

[eod_blaster]

Hippo, thanks, exactly what I needed. Not trying to become an engineer on this, just the basic's!

 

[dcfatboy]

Once you get into dynamic CR the cam specs come into play, ie you can play the cam specs against the static CR to achieve a specific cold cranking pressure at a given altitude

Hippo, are dynamic CR and corrected CR the same?

 

[HIPPO]

Different people use these terms differently.
To me "corrected" CR is when taking engine growth due to temp into consideration, and "dynamic" CR is a calculated number taking cam spec into consideration.

 

[dcfatboy]

Ahhh. I see. Thanks

 

[HIPPO]

Don't take it as an absolute though.

When you get real technical, mostly with engines that do not have the enormous heat related growth as these the way to look at it is that "corrected" will take cam specs into consideration and "dynamic" will also take VE into consideration. In this sense the dynamic CR changes at different rpm levels and will reach max value where VE is highest, ie the TQ peak. Old friend BMEP comes back. LOL.

At the level these engines are most often figured out it doesn't much matter wether you call it corrected or dynamic. LOL.