SBC oil pump & pressure question

[ian_uk1975]

I'm currently running a Melling Select 10550 HV (+25% vol) oil pump on my 383. I didn't really want an HV pump as I'm running tight-ish bearing clearances, but I was anxious about the stock Melling M55 pumps due to the problems some people seem to have with them. The stock volume Select series pumps weren't available from anywhere I could find in the UK at the time, so I took the 10550. With 10w30 oil, my hot idle oil pressure is 56psi @ 950rpm and 90psi @ 5,000rpm. When cold, it's easy to hit 100psi+ on the gauge. What I don't understand, is why my oil pressure can be getting so high, as my understanding is the oil pump should bypass oil once the bypass orifice has been exposed? I've tried to max-out the oil pressure to see if/when oil starts being bypassed, but I've briefly had it to about 110psi+ and the pressure showed no sign of abating. The pump came with a spare spring for slightly lower pressure, but I think even the installed spring should start bypassing oil @ 70psi, so why am I seeing so much more?

Should I change the spring for the lower pressure spring? Would this make any difference given the above?

Would I be better-off swapping the pump out for a stock volume pump? Logic tells me this wouldn't have much effect on peak oil pressure though.

Thanks.

Edited by ian_uk1975 on Sunday 26th February 23:21