I wonder what lifters are in that crate motor? By this I mean are the the M-6500-R302's or the M-6500-R302H's? If you remember the crate motor part number you could call Ford Performance and see if they would have an idea as to which lifters are in it. If it is the M-6007-XB3 then on that instruction sheet (see attached) it just says "Current production lifters".
This excerpt is from the 2020 Ford Performance Parts catalog on page 138:
M-6500-R302H DESCRIPTION
It’s not often that little changes can deliver big results – but in the case of the Ford Performance R302H Lifter, that’s exactly the result.
Before getting into the technical details of the lifter, here’s the background on why and how this special lifter was developed by the engineers at Ford Performance. Circle track racers who use the production hydraulic roller lifter in 347 crate engines reported that their engine seemed to lose power during long green flag runs. Dyno testing by Ford Performance engineers confirmed that – and showed a dramatic performance fall off over 6000 rpm with hot oil temperatures. The problem was traced to the piddle valve check ball, which would become unseated at high rpm when the oil got hot. The fix was a lighter-weight ceramic piddle valve check ball combined with a higher-rate piddle valve spring to keep it seated. The results of these two small changes were impressive – and noticeable by the racers. The power range was extended 300-400 rpm in hot operating conditions – and more importantly, the performance fall off on those long runs was gone.
This unique lifter construction for a drop-in hydraulic roller lifter is an exclusive from Ford Performance and fits any small block Ford roller cam application. While the R302H was developed specifically for racing conditions, it’s the right choice when assembling a high-performance small block that uses a hydraulic roller camshaft.
It could be that you are experiencing the issues they had with the non-H models.
I would still go to a better spring as it's just time in the river and drag motors tend to live at high rpms so they will wear a spring out faster than a street car even though its only 1/8 or 1/4 mile at a time.
www.americanmuscle.com
It requires beehive-specific retainers, locks, and valve stem seals, properly sized spring locators and shims.
