I'm just going on the dyno operators opinion. The vacuum gauge we had showed vacuum at 7000. Then as it went higher it was pressurizing they system. But with that said I don't disagree that those aggressive lobes can drop suddenly. Perhaps a combo of both?

1971 Plum Crazy Super Bee. 572 World Aluminum block with a Cope 727 & Dana 4.10 out back. 9.88 @ 138 with a 1.35 60 NA. Dialed back to 10.0’s. 4000 lbs with me in it.