Oil Pressure drop with RPM?
I have a question for you more knowledgable Vintage FF folks. I have a 69 lotus 61 with a vintage motor that seems to run good. I do not know the history, but it did pull strong at the track last summer. It had oil pressure of 50 psi and would drop with RPM's down to almost 20 Psi at 6k+ RPM. The oil light came on that has a separate sensor indicating the gauge was correct.
I have adjusted the oil pressure screw on the oil pump and now I have 75psi cold and 50 Psi at 6K rpms. Better, but why the drop with RPM???
Thanks-Brian
Pressure relief piston and spring?
I wonder if the pressure relief valve piston is sticking.
During your oil pump disassembly and inspection, did you look closely at the pressure relief components? Any concerning wear (or modifications) to the piston, piston bore, or spring? Is the spring still meeting its spring rate, or has time and temperture caused it to relax? Any edges or burrs built up in the bore that the piston can get caught on? Do you know for sure the spring that is in it is the "factory spring" for your brand of pump?
A good investigative experiment would be as follows:
- Start cold engine and idle for two minutes.
- Record the oil pressure at idle, then rev engine to 4500-5000 rpm and again record oil pressure.
- Allow engine coolant to warm up to 180F.
- Once again record the oil pressure at idle and at 4500-5000 rpm.
I'm curious to see the 'droop' of the oil pressure relief valve from low rpm to high rpm, and from thick oil to thin oil.
Had similar problem years ago
I experienced just such an issue. Turned out the gear on the pump input shaft that engages the cam was slipping when up to temp and as higher rpm's meant more resistance from the oil in the pump. It was a press on gear without a roll pin. But I have seen sheared off roll pins in the past also.