Might tear that old pump apart and rebuild it. We use a 4 vane on the vette and are at 20"+ I use them on my junk too and we are 15-17 depending on the engine its on. I think the dragster could likely use something better maybe. But we have some ither issues to fix in regard to vacuum there. I also have a Star pump and it's a very nice piece for sure but the results are similar. We don't regulate vacuum with any of them and never seen any issues with the loads we pull.