Years ago my car ran 11.87 at 111.9 mph w/ a set of bone stock 906 heads on a 509/292 MP cammed 440. I switched to a set of mildly home ported 915 closed chamber heads...no other changes and the car ran 11.40 at 117.4 mph in similar conditions. That gain in flow and a little compression REALLY woke it up. Was a whole different animal.

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax