That is plenty of pressure for any normal application. I use 65# (or in that range) on 8500 rpm stuff, 7000 rpm stuff, and normal street stuff. It has never caused an issue. This is with "normal" bearing clearances and nothing really to far out of what would be "normal"ap72 wrote:thank you for that tip. I may add an accumulator for that reason.
So to answer my original question it seems a 65lb spring is the max I would want to go?
how much oil pressure is too much?
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Re: how much oil pressure is too much?
Re: how much oil pressure is too much?
???David Redszus wrote:...As bearing clearance increases, the flow orifice is increased allowing a greater outflow flow of bearing oil but with a resulting drop in oil pressure. Now it is necessary to increase oil pressure to maintain volume flow.
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Because it is a positive displacement design moving an essentially incompressible fluid, if the pump is operating below the relief spring cracking pressure, the volume should be dependent only on RPM and to a slight extent internal leakage. Once the relief valve comes into play the overall flow restriction will reduce net delivery volume at that RPM (as some flow is recycled internally) and increase pressure (although at a lesser rate than if un-relieved) as more backpressure forces the valve to open further, which requires further relief spring compression and thus higher relief pressure. (e.g., if the relief valve piston was say 1" diameter, there would be far less output pressure variation, as very little spring force increase wold occur with the slight piston travel necessary to dump the excess flow)
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: how much oil pressure is too much?
many 1/4 mile passes on a 9700 rpm 355 sbc at 60- 65lbs, zero issues
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Re: how much oil pressure is too much?
If all the wear was proportional to the miles, then there's nothing you could do about it, don't wear shoes if you don't want them to wear out, but it's mainly concentrated at cold startups with/without high RPM & empty oil filters, so prime it.ap72 wrote: ...just the regular old "100,000 miles" bearing wear. I don't like that.
Don't unnecessary heat the oil, burst a filter casing or break a drive gear.
Re: how much oil pressure is too much?
My machinist and those of the major rebuilder with whom we do business both say the same thing about SBC wear patterns. For it's first forty years, the carb/distributor days, the SBC typically never had main bearing or crankshaft wear problems. They did always have worn rings, ridge at the top of the cylinder. Once EFI, crank triggered ignitions and moly rings came in, cylinder bore wear went away. A 150,000 mile engine might still show the OEM crosshatch. However, with the advent of overdrive automatics with lockup converters, the mains and the crank went bad. It is the lugging uphill under load at 1500 RPMs which causes the crank/bearing problems they see in used cores these days. Keep the Rs up and no worries."working great" is a relative term I guess. I use mostly moderate mileage used cores and every single one of them shows bearing wear. Not unusual catastrophic wear mind you, just the regular old "100,000 miles" bearing wear. I don't like that. My goal is to pull that engine apart at 100,000 miles and have the bearings look EXACTLY as they did when I pulled them out of the box.
Jack Vines
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Re: how much oil pressure is too much?
A totally different best but I was quite surprised to see the top fuel guys not batting an eye at running 200 psi at 8600 rpm with 70wt oil. Of course the oil looks like baby crap after just doing a burn out.
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Re: how much oil pressure is too much?
A HV pump is good for higher pressure at idle and very low rpm, but a lot of people (me including) are having issues with oil pressure dropping of at high rpm. It seems to be specifically related to the HV pump.
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Re: how much oil pressure is too much?
Belgian1979 wrote: but a lot of people (me including) are having issues with oil pressure dropping of at high rpm. It seems to be specifically related to the HV pump.
You need a different pan if you are seeing that.
I run a Big Block pump with a 50 lb spring on my 9000 rpm small block just for the added volume. That is all you need.
GURU is only a name.
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Re: how much oil pressure is too much?
Upon recently examining the oil pressure traces from a six cylinder turbo motor, I was rather suprised to see oil pressure fluctuations in excess of 20psi (65-85psi), at very similar rpms (4800-4900). The fluctuation occured at 1.45Hz and varied in amplitude with increasing rpms. And this was from an engine running on the dyno.Because it is a positive displacement design moving an essentially incompressible fluid, if the pump is operating below the relief spring cracking pressure, the volume should be dependent only on RPM and to a slight extent internal leakage. Once the relief valve comes into play the overall flow restriction will reduce net delivery volume at that RPM (as some flow is recycled internally) and increase pressure (although at a lesser rate than if un-relieved) as more backpressure forces the valve to open further, which requires further relief spring compression and thus higher relief pressure. (e.g., if the relief valve piston was say 1" diameter, there would be far less output pressure variation, as very little spring force increase wold occur with the slight piston travel necessary to dump the excess flow)
Bill, can you offer any suggestions as to the cause and cure for fluctuating oil pressure?
Re: how much oil pressure is too much?
Dont be afraid on the 302 Z-28 Factory Oil Pump and pan. Good HV pump with excellnt baffling.
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Re: how much oil pressure is too much?
The pan was different AND the stroke was 3.00 NOT 3.75". That is where people get confused.......rocks409 wrote:I thought the z 28 pump was std. volume-high pressure ?
GURU is only a name.
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Re: how much oil pressure is too much?
David Redszus wrote:...Upon recently examining the oil pressure traces from a six cylinder turbo motor, I was rather suprised to see oil pressure fluctuations in excess of 20psi (65-85psi), at very similar rpms (4800-4900). The fluctuation occured at 1.45Hz and varied in amplitude with increasing rpms. And this was from an engine running on the dyno.
Bill, can you offer any suggestions as to the cause and cure for fluctuating oil pressure?
The first two that come to mind are 1. Some kind of vortex/cavitation issue in the pick up that causes periodic air/vapor embolisms; the resulting 'packets' of compressible fluid could cause such pressure fluctuations. 2. Resonance of the relief valve poppet/spring system, excited by gear tooth-induced pressure pulsations. One more would be an air pocket in the system or a 'springy' section of oil passage that could resonate when excited at the correct frequency by one of the aforementioned mechanisms.
Felix, qui potuit rerum cognscere causas.
Happy is he who can discover the cause of things.
Happy is he who can discover the cause of things.
Re: how much oil pressure is too much?
af2, I don't see what my post has to do with pan or stroke. rally mentioned the z-28 pump is HV. I questioned that.