I saw Shannon Jenkins running Pro Mod at the 1/8 mile Kennydale, TX strip, back when he was running Reher-Morrison power, in a full custom '67/'68 Camaro. I observed him make a miniscule wickerbill (Gurney flap) adjustment on his rear spoiler that I perceived was meaningless. But with Jenkins making the adjustment, and David watching, I readily accepted that brain trust was worth believing. Of course this was ultra high HP, monies no object body design, yet just an 1/8 mile track.