Recently, I just finished a motor for my drag car and slid it in place... I had payed very close attention to botttom end assembly double and triple checking all measurements along the way (plastigage, etc...) and have now run into an interesting issue. When the engine is idling cold I get approximately 50 PSI oil pressure with VR1 50W - after oil temp reaches about 160, the idle pressure drops to 30-35. This is all good - BUT - the second I hit the throttle, the pressure begins a steady slide down until it reaches about 5-6 PSI and comes back up close to 30 when I release the throttle. I have a Hamburgers full sump pan, 8" deep with windage tray, high pressure pump etc... So here are my questions that maybe someone can offer some insight on:

1. Though it is a full sump, I see where companies like Moroso rate a full sump pan at 7 quarts - that seems low to me. I am running 9 qt's in this pan. Anyone have any ideas how much I should be running? (No dipstick provision)

2. Could this condition (low pressure at higher RPMs) be caused by the pick up tube being too close to the bottom of the pan? Makes sense to me, would like to see if anyone else has had experience with this condition.

3. I don't believe this to be a bearing clearance issue since pressure is stable at lower RPMs and clearances were validated to be 0.0015 on the mains. I am open to any information that would lead me down that path however.

I recall from one of my first rebuilds a long time ago that excessive bearing clearances caused a low oil pressure condition throughout the RPM range, but I do not recall it going in a negative direction when throttling up.

I have changed the oil and filter twice to ensure the assembly lube was not getting trapped in the filter and contributing to this. I am using, as stated above, VR1 50W and Napa Gold filters. This is a 454 block bored to 459, Brodix heads 13.9 CR, alcohol injected etc. The pump is a Melling HP pump with a screw in pick up tube. Because the pan is standard depth at the rear of the pan, the *only* thing I didn't check when assembling was the clearance of the pickup tube - however, I've always run them at about 3/8" without any issues. Hard to imagine this one would be that out of tolerance...

Does it seem like this condition is cropping up due to starvation?

Any and all help is *greatly* appreciated.

Thanks!

Low oil pressure with increasing revs indicates that insufficient oil is returning to the pump. The possibilities are that the oil is foaming, the pump is having pickup problems or leaking internally, unstable bypass valve, full flow filter reaching capacity and the bypass valve not opening, insufficient drainback.

Your clearances sound good. Usually, excessive clearance results in low idle pressure that picks up with revs but continues to be low relative to engine RPM.

One problem encounterd at high revs is the oil frothing. A lot of air gets trapped and then this foam is drawn into the pump resulting in falling pressure. A good crank oil stripper and windage tray help to steady the oil in the pan and let it degas to reduce foaming.

The oil pickup needs to be right down at the bottom of the pan. Like a not more than a quarter inch clearance. Too much space allows a vortex to form and the pump sucks in air. A factory style guide should be used on the pick up tube rather than nothing or just a screen. The guide helps smooth the incoming oil and resists the formation of votricies.

Internal pump leakage occurs when the gear to housing clearance is excessive both end clearance and gear to side housing, the gears are loose on their shafts allowing them to move around and or chatter. These things allow leakage out of the teeth, they tend to get worse with RPM. Chatter is often helped with a small mill vrove in the end plate to bleed a little pressure into the shaft bushing or the gear.

An unstable pressure by-pass, where the check valve begins to vibrate allowing pressure to vent back to the pan. This is hard to check for on the engine, it needs a lab to set it up and run the pump so the bypass can be observed.

The oil filter, if the engine is so equipped, has a pressure bypass valve usually in the filter or the filter adapter on the engine. If the filter is both out of flow capacity and the bypass fails to open, the result will be falling oil pressure against increasing RPM.

The lack of a sight window or a dip stick doesn't allow you to really know what the oil level is inside the pan. Bast alternative is to put it on the bench and measure its capacity. but you really should have a means of quickly measuring oil level.

Some other things to consider are oil getting away from the pick up under acceleration or braking. A well around the pick up with some trap doors to allow oil into the well but trap it against leaving is a good idea. Top end drainback may not be sufficient, many top end mods that reduce and redirect drainback are intended to be used with a drag engine that has restricted top end oiling. These things can hamper drainback on street, circle track, or  road course engines where lots of top end oil is necessay for rocker pivot and spring cooling.

So there's a couple things to ponder.

Bogie   

I am running restrictors in the top end since it is all roller - a configuration I've used many times in the past on other drag cars with great success.  All returns on the block and heads have been smoothed and optimized to get oil back down as quickly as possible. The bypass-style filter adapter has been replaced with a billet non-bypass type. I'm starting to think I am seeing one of three potential scenarios:

The pickup is too close to the bottom of the pan

The trap door bafflles are stuck closed not letting oil get back to the back of the pan

The oil pump is bypassing and getting stuck until RPM drops.

I'm leaning towards one of the first two... Unfortunately, I won't have a chance to validate until the weekend.

If the sump to pan clearance is so small that it is cutting off oil flow, why do you have sufficient pressure at low RPM?

Less demand. You could probably breath through a straw while you are sleeping but try to do it while you're running...