Header evac system
 

Take a look at this youtube video. I did the same test under similar conditions with a leaf blower and I got the same results. With regards to the placement of the 1/2" pipe venturi tube for the evac system. You actually will pull more vacuum inserting the tube straight into the exhaust flow with the 45 degree cut facing towards the exit. This is not the way it's traditionally done but it does pull more vacuum in that configuration. To clarify insert the tube at 90 degrees to the exhaust flow with the angle cut facing the exit. Just an FYI


https://www.youtube.com/watch?v=uL4rnN-Sr9M

After going to vacuum pumps on my big power builds, I don't think I would ever go back to a header evac system.