I'm having a poor top end pull. The car has 60ft times of 1.680 & runs 12.30 @ 107mph(2400lb car) with 4.10's & street tires. Car goes great 1st/2nd & as you seem to grab 3rd & 4th it lay's down on me. Now I lean it out & gets worse/ riching seems to help but wants to flubber bottom end. Now the motor was just built up. 306 dome pistons(9.5-10 to1), .595"int/.572",224'int/230'exh,110 seperation/GT40 iron heads 1.84/1.54 & explorer intake home ported,1.72 rockers,65mm TB,75mm<AM,24lb inj., 190lph.,A9l with SVO Extender. Run 15'/43-45lbs fuel stk rails & lines. I was blaming the cam but I'm leaning towards fuel. Still running air temp sensor in intake as well. Ignition is Accell dist. & modual with MSD coil. What do you think??  

What valvesprings did you install on the heads? Sounds like maybe the springs are going away at higher RPM.  

Yeah. I contacted flow tech,running there cam & he's telling me the same thing. Not near enough spring(110/330).Crane doubles 99838. I've been advised from him to go to a beehive spring, has anyone done this??  

Phoned Crane tech line @ asked them about better spring to sneek in there & he figured I'm not having so much springs going away, but stk. ford hyd. roller lifters that can't handle that lift load. Has any one gotten away using stk lifters or is every one dropping in after market lifters with there big hyd. roller sticks? I did have some lifters clacking @ idle after 3 hard passes @ the  track now that I think about it & then went away. What you think?  

did you put in a high vol pump w/ stock pan?  maybe runnin out of oil & lifters are collapsing?  if no maybe try a vac resivoir as you may not have enough vacucum to by pass enough fuel in regulator.  as vac decreases then the added fuel you added isnt getting bled off @ idle by the regulator w a poor vac signal how many " @ idle?.  

Thanks for the replys. I've since fixed my problem. You can only go so far with stockish Exlorer heads & intake for flow & performance N/A. I tried heavier springs(same) as well as I threw in a set of lifters(same). Finally got to the point I bolted a nitrous kit on (150 shot) & it finally pulled & performed the way I thought it should.... I'll be puling the heads & intake for aftermarket Edelbrocks & a solid roller cam this winter & long tube headers & hopefully be as good as with the juice. I figured my stockish motor combo was good for may be 300-350hp on motor. I like to think that it has 450hp w/NOS. I never made it to the track after,but I had a couple goes with a buddy & he use to walk away on the top(11.90) car & now I crank him hard on the top. My MPH went from 107- to 116 thru the end. ....WOW nitrous...............