Oil pressure drops at hi RPM.....Stumped

[cjperformance]

How well is your oil deairated? I have had to chase a similar problem but in a shorter term rpm combo BUT in a wet sump. A long length of high pressure clear tube in this instance showed the problem instantly. This was in a ford clevelend and was already using an external main feed line, substituting this for clear hose looped past a video camera showed it up.

[mag2555]

As posted above I would look for airation kicking in above 6500.
This was even found to be a issue on some big Loco engines that do not top 900 rpm with a dry sump system!

[racear2865]

Ive got a customer with a 355 we just freshened up. No big changes. On dyno, looked great. In the car as it approaches 7000 rpm, pressure begins to drop and drops. Cannot find any thing wrong. About to conclude a crack between channels someplace. No cheap parts. Was run on dirt track entire year, then made no changes and put on bracket drag. Changed oil pan and other small stuff, no changes.
reed

[Racerrick]

the first poster has way too much pressure for a sbc! 65 is all you need. the oil is too cold to flow properly. if all the obvious solution don,t help the pump most likely cavitating. increase the pickup tube diameter. use suction rated hose. slow the pump down. smaller pump. I prefer Motorcraft brand 7.3 diesel filter fl1995. it is readily available, the newer ones are very efficient, 95%@18 microns and still flows 20gpm , burst is 200psi and 30gram capacity.

[Newold1]

Talk to the guys at Peterson who have speed record car experience. They will be able to better analyse and help you research the issue or they can contact some racers in that arena who have experience with this type of issue. Some simple thoughts, was pump pulley matched to sustained rpms, how far and what is routing between pump and tank, where is oil pressure sensor mounted in system, is the oil pressure measured mechanical or electronic. what type , size and brand # of oil filter, are pump inlet lines reinforced or hard wall, what is actual oil being run, have you tried raising oil temp to about 160 degrees, is engine using spring oilers in addition to piston squirters, what's the windage configuration. Just throwing out some thoughts.

[R.Brown]

I did not read any responses, but do you have some kind of internal support to the scavenge lines, and the supply line from the tank? Also what size are the lines? I've personally seen things like this happen on the dyno, and have since then never build a dry sump system without using internal support coil on any suction line. Now-a-days there are some places that make vacuum service hoses that do not require the coil installation, a place in NC... name escapes me... ahh, Brown & Miller.

From memory, The vacuum rating on hoses is at ambient temps, and is a whole 'nother story when up to normal oil temps.

Just a thought,
ryan

[leahymtsps]

The bottom of the tank and the pump are at the same level
yes there are 2 tube 90's one at the tank and another at the pump. the supply line is -12
oil pan is a Dan Olson right side kickout, scraper, windage tray, #12 pickups, separating diverters, and capturing trough
the pump is a peterson 4 stage. 2 to the pan and one to the valley

Personally I would be using a -16 supply line


Tom

[Turborick]

got a restrictive filter element between the pump and engine? or between the feed and pump? Sounds like restriction or cavitation somewhere.

We run a K&N hp-3002 filter
the feed line to the pump is a -12 with a flat spring inside
I agree with the cavitation theory

[Turborick]

slow the pump down. too much pump rpm

I think im going to try this next

[Turborick]

Suction hose collapse maybe? From tank to pump.

flat spring in feed line

[Turborick]

I expect your HP is well into four digits, but 100 + psi still seems way high. We run ~ 60 in our 750 HP/8300 RPM SBF road racer..

Where are you tapping in for the pressure signal and could you perhaps tee in a second sender immediately after the relief valve to see if there is an excessive restriction?

pressure transducer is feed from 1/4" plug right above the stock filter boss
relief valve is integral with the pump

[Turborick]

I have seen large main or did clearances cause this. In excess of .028r.030m. It hears the oil up real quick. What's your side clearance in the rods and litter clearance. ?

bearing clearance are .0024 / .0028
don't know what the rod side clearance is what should it be?

[Turborick]

How well is your oil deairated? I have had to chase a similar problem but in a shorter term rpm combo BUT in a wet sump. A long length of high pressure clear tube in this instance showed the problem instantly. This was in a ford clevelend and was already using an external main feed line, substituting this for clear hose looped past a video camera showed it up.

I looked in the dry sump tank right after a dyno run and didn't see any airation the runs lasted about 30 seconds
clever idea with the clear line and camera

[Turborick]

the first poster has way too much pressure for a sbc! 65 is all you need. the oil is too cold to flow properly. if all the obvious solution don,t help the pump most likely cavitating. increase the pickup tube diameter. use suction rated hose. slow the pump down. smaller pump. I prefer Motorcraft brand 7.3 diesel filter fl1995. it is readily available, the newer ones are very efficient, 95%@18 microns and still flows 20gpm , burst is 200psi and 30gram capacity.

I might try lowering the pressure but for now I will try slowing down the pump first if that works I will put in a smaller pump section
running a -12 suction hose with a flat spring inside and at this time no room to go to a -16

[Turborick]

Talk to the guys at Peterson who have speed record car experience. They will be able to better analyse and help you research the issue or they can contact some racers in that arena who have experience with this type of issue. Some simple thoughts, was pump pulley matched to sustained rpms, how far and what is routing between pump and tank, where is oil pressure sensor mounted in system, is the oil pressure measured mechanical or electronic. what type , size and brand # of oil filter, are pump inlet lines reinforced or hard wall, what is actual oil being run, have you tried raising oil temp to about 160 degrees, is engine using spring oilers in addition to piston squirters, what's the windage configuration. Just throwing out some thoughts.

Peterson speced out the hose size and pump speed for our 9500rpm sbc
hose is 5' from tank to pump no tight bend mostly straight with a flat spring inside
pressure transducer is feed from outlet above the stock filter boss
filter is a K&N HP-3002
oil is 5W30 Quaker State Ultimate Durability
this problem was not as bad when we ran the oil a 110 deg F so don't want to heat it up any more till we figure this out
no spring oilers
pan is a dan olsen left kick out aluminum with built in scraper