Thanks for that Chuck, I knew what I meant, just didn't use the right word. I looked it up and found this article, it's pretty interesting.
http://www.enginebasics.com/Advanced%20Engine%20Tuning/Static%20vs%20Dynamic.html

Here is another from Comp cams, look at question #10.
http://www.compcams.com/v002/Pages/404/camshaft-faq.aspx

In my 250 I have a set of Rhoads variable lifters. They bleed off at low rpm and pump up at higher rpm, thus changing the duration and cam events. I get a much smoother idle yet still have the full benefits of a slightly larger cam.

Joe

1937 Chevrolet Inline-powered Streetrod