FYI, the M23A in my spares dumps pressure at 57 PSI. Spun it with a 1/2 inch drill motor in a 270 GMC engine and watched the pressure gauge I had hooked to the block. Pretty linear pressure going up until about 600 pump RPM (1200 engine RPM) when it reaches 57 PSI, then stays there to the drill's rated speed of 850 RPM. Oil was 10w30 and temp was around 45F. Gauge was a 4" diameter fluid dampened model rated at +-1PSI.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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