I have been having this odd problem and am hoping someone on here may have some ideas. Here is the motor
4.030 bore 4 bolt main
Eagle 4340 forged crank 3.75 stroke
6" H beam rods
SRP Forged 12.9:1 pistons
Total seal gapless rings
Cleavite H bearings
Comp cams 4/7 swap Mech. Roller cam
Comp cams roller lifters w/ rev kit
Oil restrictors in back of block.
Lifter galley's have been plugged and screened.
World products heads with + .100 valves and pushrods to correct geometry

I can give more detail if necessary. this motor runs on Methanol and puts out around 640 HP.

now the problem.. The first night out i had great oil pressure. then my warning light came on. it was down to around 10 psi. i took it home and measured all bearings etc. every thing was fine and looked good. I put a new Moroso racing oil pump on, new pick up tube ( and set it to 1/4" from pan bottom, and a new oil pan. this is a circle track car. The next race it was golden. 8000 rpm's and oil pressure to spare. then this last Saturday night the light came back on and i was at zero oil pressure. I pulled into the pits and we started looking. pulled the oil line and no oil was pumping out. I pulled the dist. and turned the oil pump shaft with a long screw driver. Oil squirted out of the oil hole. scratching my head i stabbed the Distributor, set the timing and had 65 psi at idle. then i went out and ran the entire main event with plenty of oil pressure. This motor is spotless inside, Distributor to oil pump drive shaft has plenty of engagement. I was thinking maybe the bypass was sticking open on the pump. but 2 brand new pumps? I run HP4 oil filters and change them every race along with the oil. Myself and all the engine guru's localy are all scratching our heads. so if anyone has more idea's let me know. I will try everything. also, i checked and the rear cam bearing was installed correctly.