bingo

When I start my car I have about 55 PSI. After it warms up I usually have 35 PSI. Today it started dropping pressure when I accelerate. It gets down to about 15 PSI. I verified this with a mechanical guage. The engine is a 355 built by a local machine shop. The heads and cam are an LE1 package. When the pressure drops the power remains and the engine doesn't change sound. The oil pump is a standard pump with the pickup tack welded on. I did a search and didn't really find anything specific to my case. Any clues or suggestions?

SS RRR

One possibility is windage. How many quarts of oil do you pour into the engine and what kind of oil pan?

bingo

Stock pan. It doesn't have a tray, just the stock baffle. It has been fine since February. It just started earlier today. No sounds or anything.

SS RRR

How many quarts of oil do you pour into the engine?

bingo

5 quarts of 5-30. It is due to change soon, but it isn't real bad. I am running a 1060 Wix filter.

MEAN LT1

Ive seen three instances were this has happened and all three were a cracked block. Good luck

bingo

Cracked where? How? The engine has about 2500 miles on it. It has never been run hot. I am going to be very unhappy if this is the case. I have read every post I can find on this subject and everything says LT1s are bad to do this. I am going to try an oil change Friday. I might try another weight.

SS RRR

Does this only happen when going forward? What happens when in neutral, sitting still and you hold it in the upper rpm range?

96ZCamaro

Yea, I also would want to know if it does it in neutral. But I am wondering if that one spring in the oil pump may have gone bad. Maybe sombody else will chime in on that.

SS MPSTR

couple of possibilities...pump sucking air due to windage, pick-up not welded properly to pump...the loss of pressure under acceleration symptoms you describe is the suspected cause of a few guys' engines being ruined due to cavitation while using a hv pump with a stock pan.

bingo

It doesn't do it in neutral. I can rev it to 5000 in neutral and it is fine. The RPMs/PSI raise like they should. Only under a load with the RPMs up. The spring was suggested by a friend of mine. Is this a common occurance? I don't think it is a HV pump. It came from the machine shop with the engine when it was rebuilt. It uses the bigger pickup tube. I think it is an M55S. I had it tacked in two places by a professional welder. I had a high volume/high pressure pump in my last engine. It caused the gear on my oil pump drive to strip out. What causes cavitation? I am going to research it. I am not going to drive it until I change the oil. Would heavier oil help? I read something about running it a quart low to reduce cavitation/windage. Any truth to this.

SS RRR

Run it with 4 quarts and see what happens. Because pressure is not being lost in neutral then SS MPSTR's post pretty much covers the possibilites.
I know you say the p/u was put in by a professional, but did the professional mock up the pump and p/u to the block and check the clearence to the oil pan? It's possible the p/u is positioned too high which would make it sensitive to oil levels while the engine is under load and accellerating.
Cavitation is caused when there is too much oil in the engine and not enough in the pan which literally causes the pump to starve. It would be a good idea to know whether or not the pump you have is h/v or not. Do you have a part number?

FASTFATBOY

My first engine did this, cam bearings failed.


David

SS RRR

So... even when your car was sitting in neutral and you revved up you would have good oil pressure yet when you would drive under load and accelerating the pressure would drop?
Never heard of that one before.

mdacton

a bad main will do that......when the crank gets thrust to it the oil just spills out the side.

I could see a cam bearing doing it too......when its under load it has thrust to it also.