I had a really mild 505 on the dyno last week.......the cold water test on that was a 14tq/8hp gain.

I've seen it change the numbers on a 700-800HP BBC by about 25hp.

Just depends on what it is.

68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads