Losing oil pressure at high revs

[Leadfoot]

Noticed this yesterday whilst on track at Bedford:

above 5k (ish) revs in 3rd & 4th accelerating hard, my oil pressure is droping gradually.
Normally I'd expect 40 psi & <5k it's steady there, but during sustained acceleration the pressure is falling back past 20 - recovering with each gearchange.
I've checked that the level's ok.
I'm thinking that maybe the oil pump relief valve spring is the culprit?

[shpub]

Or the pump is knackered... or the pick up in the sump is broken... or one of the baffles is not keeping the oil by the pick up

[Leadfoot]

shpub said:

Or the pump is knackered... or the pick up in the sump is broken... or one of the baffles is not keeping the oil by the pick up

1/ knackered pump - wouldn't this be worse at low revs?
2/pick up broken - same throughout rev range?
3/baffles - problem is worse as I get into the higher gears & the engine spends more time getting thru' the rev range, so acceleration is tailing off compared to 1st/2nd. This made me think it unlikely to be oil surge (no probs when cornering either).

[shpub]

Depends how and where the pump is worn. Also the faster the revs, the more oil feed is needed and so if this is reduced though pick up problems etc the pressure can reduce.

I would chcek the relief spring first but be prepared for somthing else. Is this a serp engine or not?

[greenv8s]

Does it happen at sustained high revs, or only when accelerating hard?

[Leadfoot]

Serp engine.

Not sure if it's doing the same at sustained high revs - I only noticed it yesterday on the long straight at Bedford (it wasn't doing it there 2 weeks ago), didn't notice on the way home as was only bimbling along the motorway. Will have to check on that one.

[k77-widow maker]

Bedford is a bitch for this, my precat's oil pressure was all over the place, due to the g forces being subjected to the car.

So much so that I was thinking of getting something done with the sump, like baffled if it is not already.

[Leadfoot]

k77-widow maker said:

Bedford is a bitch for this

No probs in the dry the other week, just Weds evening in the rain & only on the straight.....

[greenv8s]

After I got the suspension sorted on the V8S I used to get 'oil surge' on long sweeping high speed bends. The conventional explanation for this is oil surge within the sump. I went down the usual route of fully baffled flap valved sumps and it helped a bit but didn't really cure the problem. I came up with a theory that the problem was oil collecting in the top of the engine and not draining back. I could visualize oil pooling in the corners of the rocker covers under sustained lateral G and not all flowing back to the sump. My solution was to add more oil to the sump to compensate for the oil 'trapped' at the top of the engine in corner, I now overfill by about 1 cm before taking the car on track. I never proved this was the cause, but the problem has never happened since.

If something similar is happening to you, you might find that the problem improves/goes away when you increase the oil level - even if the level didn't look low to start with.

[Leadfoot]

Level was right on the full mark. Never had the problem before even with a lower level.

Tried to get a relief valve & spring without success today, any suggestions (Croydon area - tried the local dealer & specialist) before I contact RPI/V8D/Power & get one mail order?

[Boosted LS1]

I'd guess that at higher rpm/load conditions the oil's being squeezed out from the shells a bit faster so your oil pressure isn't keeping up with the demand. It's probably thinning a bit as well if it's non synthetic. The 20 psi you have is the delivery pressure to your shells etc, not the pressure at the shells. Has the engine clocked up a few miles? If not I'd check the oil and the pump or look for a leak.

[cartoons]

i had the same problem at bruntingthorpe.when i accelerated the pressure dropped.turned out to be the pressure sender on the sump!