The Vince Gironda Perfect Curl is an exercise that Vince is very specific about. The objective is to place maximum tension on the biceps. Start the exercise as if you're doing a regular standing barbell curl (you can use a straight bar or an EZ-bar).
Before starting the movement, bring your upper torso backward (shifting your weight toward the heels). Note how the shoulders are aligned behind the hips and knees in the starting position. Now slowly curl the weight up from that position.
As you lift the weight you're going to slowly bend the upper torso forward so that in the end position the shoulders are in front of the hips and knees. Lower the bar using the opposite motion. Start in the torso forward position and as the bar is lowered, bring the torso to the backward position.