Vacuum Secondary in Action

What ACTUALLY happens when you floor a Vacuum Secondary Holley. This is on the 360 in my Van. Thank the Van :)
Enjoy

One thing I do love about working on a van is the engine is right there after the doghouse is removed. With the weight of the van and the rear gearing we had to put a stiffer spring in to keep the 600 carb from bogging. The stock silver spring was too weak, so think we went to the brown. Good stuff!