Last winter we messed with our moroso header ev system because we had a problem with the check valves rusting and gettin stuck, I cut the weld holding the tube in the collector < open headers> and played with moving the tube around while running the engine @ 2500 rpm to find the spot with max vacuum, I also booted the check valves and found some more vac with out them, With the morosso system installed as per their instructions we made around 2 to 2.5 inches, I posted last year about anyone not running the check valves cause I was not sure if this was gona be a problem and for the most part had not found anyone blowing up on a back fire. Raff posted a pic of a curved e vac tube that was square with the collector tube so I tried it out and found some more vac that way, I also found that the breather cap tube was too close to the baffle in the valve cover and found some more there, So by the end of messin around we more than doubled the vac @ 2500 rpm, I have seen as much as 5.5 inches and have not blown up yet. As far as power goes I cant tell any difference but no more oil leaks