Those springs may be your problem.
Last year we took my 72 Duster to the track
408
Trickflow 190
11.2 compression
Howard Solid 600/615 254/260@050 108 in at 103.5
Strip Dominator
800cfm DP
727/3500 4.10 / 28
I am pretty sure the springs are the same as you got on the big block heads. They are rated at 120 on the seat and a pac spring isntalled at 1.9.
It only did 113.5 in the 1/4. Something was definitely wrong..
After talking to my friend Mike we took off some springs and tested them. We tested a few at the install height and were only getting like 110 and you could see the scrub pattern on the tops of the valves had been moving around. The valves had been turning.
We started looking to try and find another spring that would work with that same install height and everything and ended up ordering Howards HRS-98632
Valve Spring Set Series:
Max Effort
Style Of Spring:
Dual
Outer Overall Diameter:
1.500
Outer Inside Diameter:
1.100
Inner Overall Diameter:
1.100
Inner Inside Diameter:
.816
Damper:
No
Closed Pressure:
145 @ 1.940
Open Pressure:
422 @ 1.250
Rate:
413
Max Lift:
.780
Coil Bind:
1.100
This ended up being a spring pressure of about 155 Seat Open 390/400 area.
We brought it to the track this year and the car did 118.5. We were not quite wide open we discovered the previous year but it wasn't by much.
I think your issue is those springs. I had wished I had bought the heads with the one size stronger spring.
The howard springs went right in though without anything else needed to be changed. Perfect for the 1.9 install height and everything. Went right in and they are not expensive. They are lik $140.
Howards Cams 98632 Howards Cams Performance Street/Strip Valve Springs | Summit Racing
I am also running there EDM oiling solid lifters. I would imagine when the spring breaks in a little the spring pressure will drop some.
