Dynamic compression.... anyone know much about it?

[RomanV]

Okay, so i'm trying to get my head around the idea of dynamic compression. From what I can gather, it's the compression ratio that's measured from the time that your intake cams shut, to when the piston is at TDC.

But what relevance does this really have?

I've heard that if you've got big cams and a big compression ratio, your dynamic compression could very well be the same as a 'normal' engine. So then what's the point? I suppose to move the efficiency range further up the rpm range.

I've also heard some talk of VVTI effectively altering your dynamic compression, which makes sense. So I can see why you'd want a higher dynamic compression at partial throttle, but why would the cam advance or retard as your rpms increase? Is it related to the VE of the engine?

I think I've half got an idea of the relevance of it, but I cant really find anything useful or helpful on the net.

[Pelo]

This guys website is quite good. Thats about the limit of my knowledge on it though!
"Specifically, the intake valve closing point is intimately related to an engine's dynamic, or "effective" compression ratio"
http://e30m3performance.com/myths/more_myths1/comp_ratio/comp_ratio.htm