My dad used a Vari-cam on his Pontiac for a while, it work really good. James Rhoads invented them way back when, then switched to the variable leak down lifters still produced to today. The lifters in my 250 work pretty good considering the weak valve springs. Stronger springs and steeper cam lobes make the lifters work better, as mine don't have the pressure needed to really bleed down. They change the cam profile by not opening the valve as fast, not lifting as much and closing the valve sooner. Once the oil pressure comes up and over powers the springs, the lifters go almost solid so you get the most out the camshaft.
A simple way to describe them is having very loose valve lash, till about 2500-3000 rpm, then it goes back to normal.
Joe
