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SR20 New Build Too Much Oil Pressure, please help

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Hello everyone,

How damaging is it having an engine that operates with high oil pressure? My main concerns are oil leaks, oil consumption, damage to engine bearings, damage to turbo ball bearing (has a 1mm restrictor), damage to oil filter and damage to oil cooler (I don't think it is rated for above 10bar).

I have pretty much convinced myself that this much oil pressure is not acceptable however i'd like opinions from others as this is my first engine build.

10 bar of oil pressure @ 5000 rpm. 1.7 bar @ 800rpm. Oil is 5w30.

I did a comparison between some logs I had from other cars to see how each engines oil pressure behaves as a function of rpm.

I recently finished building my forged sr20. Upon first start it had high oil pressure. It seems to me the oil pressure relief valve is not working correctly. The oil pressure sensor was newly added when this engine went in. I have verified the reading with a mechanical guage. The engine bearing clearances were done to just looser than oem spec. Nismo race bearings were used. Oil pump was not replaced during the rebuild but was inspected. Oil pressure relief valve was found to be stuck however was free'd up and then I polished the valve and reassembled and it moved smoothly. I believe I ended up using s15 vct oil PRV springs in the redtop oil pump, they were slightly stiffer. I have verified that oil cooler/filter relocation lines are not the wrong way around.

I'm not sure if high oil pressure to plain bearings causing damage is a bit of myth. Any info on this myth would be good.

Any comments or feedback is appreciated.

Thanks,

Jarrad.

Attached Files

That is consistent with a stuck pressure relief valve in the oil pump and/or too much spring force.

It's a pain in the bottom, but I'd suggest pulling the pump back out and re-checking the pump relief valve is still free to move in the bore and, if that's free, consider a slightly lighter spring - it also be due to excessive shimming, if you've done that?

Back in the day, it was felt that excessive oil pressure could scour, or de-laminate, the plain bearings - I haven't any confirmation either way. At a minimum, though, the power needed to drive that pump is going to increase wear to the drive mechanism and cost flywheel power.

Back in the day, the default would be 10PSI per 1000rpm.

Thanks for your feedback! Much appreciated.

I didn't shim the PRV, I had a shim and was going to but decided against it.

I suspect that the springs are too stiff in the PRV.

On the sr20 it is a pain to take the oil pump completely off. I'm hoping I can get just the PRV off with the engine in the car.

I have heard of that 10psi per 1000 rpm rule before, doesn't make sense to me that oil pressure would be linear with rpm since their is a PRV in the system. Maybe 10psi per 1000 rpm untill you reach the point that the PRV opens.

Well done diagnosing.

That engine and most filters, coolers, are perfectly happy with 6-7 bar oil pressure for example, but 10 bar is beyond what some components can handle. Risk to seals, coolers, becomes concerning.

Yup as you mentioned oil pressure will increase with RPM rapidly, then plateau somewhat as the PRV bleeds some pressure off. It's not uncommon to blow past the PRV pressure, but certainly not to 10 bar.

In terms of the turbo, there are regulators designed to control turbo pressure feed if you want to ensure you don't over pressurize it.

Hi guys,

Good news! Oil pressure relief valve is fixed!

I was able to get the oil PRV off with the engine still in the car which I didnt have my hopes very high for, I had to use a chopped up socket to get the job done.

Turns out, when rebuilding the engine I had used a PRV spring from a sr16ve oil pump in a sr20det oil pump and the 16ve PRVs have a much stiffer spring and a much shorter stroke for the PRV. Hence, using the sr16VE PRV spring in a DET oil pump housing, the PRV had heaps of preload and never opened.

Got the job done though. Graphs with the new pump curve are attached. Thanks for your help, was greatly appreciated.

Time to make some boost.

Attached Files

Hey man. I am having the same exact issue. Howd you get to the relief valve without pulling motor. Can you get in there by removing lower pan and girdle?. I am trying to avoid taking the pump completely out. Any advice is appreciated

i have 55psi at idle hot. And 120psi at 4k rpm. The motor is all stock internals. It sat for some time prior to me bringing it back to life.

Can't help you, Alex, but following on from my previous comment, which I thought I'd already done.

Jarrad, there are two main aspects when looking at the oil pump.

It has to have sufficient volume to overcome the internal leakage - through the bearings, oil squirters, follower squirters, etc - so it has sufficient oil pressure to pump oil to lubricate at the furthest parts of the engine, whether hot or cold. This flow volume is roughly constant through the rpm range.

The other is there needs to be enough oil pressure at the main bearings to overcome the centrifugal force on the oil in the crankshaft that is being thrown back against the oil trying to enter the crankshaft oilways from the main bearing - this is where the 10PSI per 1000 rpm 'rule of thumb' came from - some engines need more (Pontiac used much larger main journals and it was more like 15/1000), some smaller engines need less.

The reason the oil pressure increases with rpm is that pressure is just the measurement we use for the resistance to flow. As rpm increases the pump is trying to force more oil through approximately the same internal leaks, and as this gets harder to do the pressure increases more and more - in extreme cases it can explode oil filters, oil coolers and do all sorts of damage.

To get around the two different requirements, traditionally* oil pumps are made to have sufficient volume for the idle oil pressure and will use a spring loaded valve that opens to increase the 'internal leakage' and prevent excessive oil pressure. Get the spring seat and rate wrong and you can run into issues, such as you found.

So, for the most part, "high volume" pumps are a waste of money, unless bearing clearances and/or other factors have significantly increased the 'leakage'.

*I say "traditionally" because several engine manufacturers are now using variable rate pumps, where rather than bleed off the pressure the pump is designed to reduce the volume for each revolution - balancing that against the rpm it's operating at to maintain the correct flow and pressure, while minimising power wastage from bleeding off the already pressurised oil.

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