Scenario...ITC Honda 1500, carb. Fresh, Mobil 1, 5W-30 with new Fram HP1 filter just as I always run, no change. Total capacity with cooler is just shy of 5 quarts. Everything checks out nice and tight with no leaks, etc. Idle pressure is 35-40 lbs, racing is 65-70, temp at race it 210 in 80 degree temps. At full speed, 4th gear, about 6G and climbing, oil pressure light comes on and pressure drops to 40lbs, stays there, then pops back up to 70lbs., stays there the rest of session. Later sessions, same thing happens, sometimes in turns, sometimes in short straights, once for half a lap. Pressure never goes away lower than 40 lbs and always comes back up to 70. Oil level and temperature remain good. Can't get it to repeat in pits.

Ideas...theories...I'm fresh out of spare bottom ends.