Solid Flat Tappet Valve Springs

Fuel pressure?
That's what my machinist suggested. I run a decent mechanical pump. I believe its about 90 gpm. 26/10/15 slick 4 speed, 3.55/ 3.91. 4.30 no exceptional change in 60'. I swapped to a 11.5;1 360 and a Schneider grind 246/.510 solid on 110 with 308 heads and same spec valve springs. 1.94 1.6 valves and it comes on a lot stronger. Shelfing this car and working on a 1984 Daytona for this season.