My car has a built 355 with about 12k miles on it. it runs strong oil pressure at idle cold is aroun 60-70 psi and once hot around 25-35psi and when the Revs come up the pressure hot jumps to around 50-60

Here is the problem, Sometimes when I get on it hard in first or second when the RPMs get over 5k the oil pressure drop from 50-60 to 30-40 is this going to hurt my motor? it doesn't semm to drop below 30PSI when it does this but I thought it was weird. what could be causing this to happen? is the oil sloshing around? or is it somewhat normal for it to happen in the higher rev ?range shift point is aroun 6500 rpms only does it under HEAVY LOAD

 

Mine does it too.

 

what kind of oil pump and pan you running? windage tray?

 

Sounds like windage.

 

If your looking at your stock gage you should really get a mechanical on it and put it in the car with you so you can verify. I can tell you that mine looked to be running low but when I got the mechanical on it I saw 10 to 15 psi over what the stock gage was saying.

 

...or perhaps cavitation. The question about the pump and tray needs to be answered.

 

Okay some details on my problem which is similar to the OP's.
Melling 10554 standard volume pump with white spring and Mobil 1 5/30. Stock pan and windage tray. Rest of stuff in sig. Yes I also have a mechanical gauge that show the drop just like the dash gauge and the bypass in the spin on adapter is hard plugged.

First or second gear WOT oil pressure is around 50# till around 4K RPM. At 4k RPM it drops to 35# until around 6K RPM. At 6K RPM, it shoots back up to around 60# or so. Pressures are great at all NON WOT ranges.

I stated in another post the recently my pickup fell off and I had bad pressure loss when hitting the brakes. That has been fixed and there is no obvious engine damage and the pickup is between 3/8 -1/2" off the floor.

I noticed this WOT pressure drop behavior months ago prior to the pickup falling off so I dont think its a new problem as a result of the pickup falling off.

I have run oil level to the MAX range on the dipstick as well as a half quart overfilled. Problem remains. I am gonna try running a half quart underfilled plus remove the K&N oil filter and put the Wix back on too. Might even try some 10/30 oil but that will definitely raise the pressure everywhere. Right now my idle pressure is around 20-20#.

It seems g-force related to me like the oil is climbing the back of the pan because the problem is less obvious under softer acceleration. So if that is the case what makes my oil pan and oil behavior so much different than everyone else's?

When the pump was out, I took it apart and it looked golden with no wear or other issues. The pickup is press fit and welded all the way around the tube.

Thoughts?

 

I cannot be sure about the pump I believe it to be a melling standard with the white spring ( I trust my builders expertise ), but the pan and windage tray I believe are stock. I cannot find my build sheet at the moment. I run a M1-302 filter with M1 10-30 also about a half quart overfill ( to account for the taller filter).

wrd1972 desribed the problem to a "T" like he said it only really does it bad in 1st and 2nd gear at WOT in my M6

I guess I am asking if this is really a problem and what can be done to fix it if need be? How common is this?

Explain windage and cavitation to me please?

 

What about the pickup hieght? Do either of you know what hieght the pickup is sitting at?
Windage is caused by the rotating parts. Just like a fan blade, as the pasrt move they create wind in the crank case so yoo can end up blowing the oil from level in the pan to one side. Stock these engines have windage trays that reduce the amount of wind that blows on the oil in the pan allowing it to stay more level.

 

Cavitaion is caused by wind and other factors. As the wind blows on the oil in the pan it moves it and can cause a stiring effect where the oil rotates around in the pan. This can cause air to enter the oil and the oil can become polluted with air bubbles. as the oil gets sucked up the pickup tube the air bubbles rejoin one another and can cause air pockets or big bubbles that enter the oil pump and cause the pump the cavitate on the air and loose pressure untill the pump reprimes itself with more oil than air.

 

not sure about the pickup height in my motor. So, what can be done to reduce cavitaion?

 

I have the same problem.
I think oil is climing up the back of the pan, gets grabbed by the crank, and thrown down into the pan. Oil will airate and cause pump to cavitate.
I should weld a plate in the back of the pan to prevent oil from climing,
but I found out that adding more oil makes it worse, so I removed some
oil and it got better. When I dropped it to the low mark on the dipstick
problem was gone. I have been driving like this for 37K miles, but the proper way would be to pull the pan and fix it right.

 

Bolek I really think that you are right. I just did a little high speed run down the highway and the problem is nonexistant in third and fourth gear, would an aftermarket oil pan with baffles fix this issue?

What kind of pan does everyone recommend?

 

My pickup fell off a week ago. It is now between 3/8 and 1/2 inch. Maybe closer to 1/2 but not more. Before it was much closer to the pan floor and I still had the pressure drop problem. I dont think pickup height in my case is the root cause.

I am going to try this:
http://www.summitracing.com/parts/MIL-32500/

Dont know when I am going to get around to it though. This should help keep the oil from climbing the back of the pan if that is what it is doing.

 

Update guys.
When I was running a quart over full, the pressure drop was closer t 4.5K RPM. When I run around a half quart under, the drop is closer to 5.5K RPM. I think the oil is getting churned when over full.

If I drive in second and very slowly pull to 6K RPM, pressure spike downward from 60# to about 35# then spikes back up. This happens very fast.

I have now convinced myself that this is NOT g-force related and that the oil is not climbing the back of the pan. I am starting to think the pan is getting sucked dry or the oil is not draining back fast enough. Funny thing is I am using a standard volume Melling select oil pump. I still intend to try standard Penzoil 5w30 at my next oil change.

My oil pressure seems very good on M1 5w30 so I am not convinced I have major bearing wear or something really bad. I have 20# at idle and pressure builds to 60# at upper RPMs. What the Hell else can cause this? Would lowering the pickup from just under 1/2" to 3/8" really solve the problem? That seems treally thin.

Maybe thinking about a bigger Canton oil pan.

 

What head gaskets are you guys running? Are you running a stock style gasket that has small holes for the oil to drain back to the pan from the head? What does the white spring do to the pressure or volume?

 

I am running the Fel-Pro .039" gaskets. Cant think of the number right now.
The white spring is used to allow the pump to achieve a higher pressure than the purple spring before bleeding off. It should provide additional oil pressure at higher RPMs.

 

Seems I once read that people would chamfer the oil hole in the rear main cap to help resolve cavitation issues. Apparently, it can cause turbulence in some cases.

 

Okay I pulled the K&N filter and installed a AC Delco filter just to rule that out. I also ran lesser amount of oil to see if it truly acted like it was sucking the pan dry. The pressure drop acts the same if its a quart low, at full over slightly over full. I now do not believe it is sucking the pan dry. I would assume that if this were the case I would also get a oil low indicator on the dash.

Starting to believe this is a cavitation problem of some kind and my engine builder is leaning toward this too. He is going to call Melling and discuss the problem with them.

This problem acts like a purge problem where the pressure is being quickly systematically purged off for a second then quickly recovered at 6K RPM. This is just friggin nuts so I am ready to blame the oil pump.

I had the white spring out of the pump just a week ago and saw no obvious issue ith it. I really wish I would have noticed if this was an issue to this degree before the pickup fell off. I noticed some drop but I never payed great attention to it and just dismissed it.

What other good pumps are out there besides the Melling select pumps?

 

Gerotor pumps are supposed to be anti-cavitation, but are not cheap.