Pressure drop with increased RPM
 

I have a newly rebuilt 460. Maybe 50 miles on it. I just got the car back and went for my first short ride (bad weather). The engine was nice and warm and I noticed when accelerating the oil pressure first dropped then increased.

My leg is broken, so I wasnt driving so I didnt really force the issue I was just observing the first run of the car.

Is this a problem? I plan on going out in the car today, should I run the car a certain way to further gather data on this issue?

Just start it up, let it warm up, then while sitting still out of gear, give it some gas. Oil pressure should go up with rpm.

If oil pressure goes down with rpm under acceleration, it could be an oil pickup/oil pan issue.

Low oil level?
Leak at or loose oil pump pickup tube?
Excessive main bearing clearance?

If you are running an oil cooler, it could be the cause also.

I once had an issue with oil pressure dropping with increased rpm's. I had just installed a new timing chain along with a new HV oil pump and pick-up tube in a 289 in my '66 Shelby GT350. When I started the engine, the oil pressure would DROP when the engine revved. The cause turned out to be a hairline crack in the (new!) oil pick-up tube that I had just bought - it was sucking air when the engine was revved up.

Jeff

Since your engine is new I doubt this is the cause but a pressure drop as rpm increase may be worn rod bearings. The rod bearing face centrifugal force from the rods bearing going around the crankshaft center line. The oil gets slung out due to centrifugal forces. Funny I just read an article last week on the subject.

what cam is in the motor? solid lifter? roller? hydraulic?

a pressure gauge that is showing a fluctuation, if you assume it is no fault of the gauge or sender, is the pan being sucked dry of oil, or a massive oil pressure leak, such as the pickup tube. a solid cam in the 385 series motors can suck the pan dry in no time if the proper restriction in the oil galley is not present. eventually it will mean rod bearing failure.
verify that the valve covers are not filling up with oil. it will make a mess but spin the motor over with ignition disabled and a valve cover off oil should be fed but not overly flooding the top end.

I'd bet on a bearing problem. Excessive clearances on the mains allow the crank to shift on leading throttle, momentarily increasing journal to bearing clearances and allowing oil pressure to drop until the pump "catches up".

I actually had the same issue with the original 427 in my Cobra, which had been run hard before I bought the car.

Having seen this brought up I will put my .02 in. A buddy of mine rebuilt a 383 Dodge motor one time for his van. He lived about 2 hours away from me and on his maiden voyage down to see me he called about half way with problems. He was graduly loosing oil pressure at highway speeds. If he drove real slow and kept the rpm's down it seemed to be ok. I took off and met up with him to see what we could do.

After we went through all the normal questions and dumb looks at one another we decided to drain the oil and have a look at it. We bought a 3 gallon drain pan from the auto parts store.....damn near filled it up....lol. He had forgot that the dip stick was the wrong one. He also forgot how many qts he had put in initialy. He filled it up untill it registered on the stick. The crank throws were cutting through the oil and severly airating it. We got the specs on proper oil amount from the parts house...filled it that level and off we went. Didnt have a lick a trouble after.

Just something to think about and possibly eliminate.

CBattaglia,

You're not alone. One of the leading 460 builders, Jon Kaase, posted this thread: http://www.460ford.com/forum/showthread.php?t=145132

No resolution has been posted, sigh...

There may be an idea or two in the long thread that could help you.

Tom

Jon Kaase found the solution. Just change to a 12" deep oil pan. :p

Actually it does seem that changing your pan and pick-up might help. What pan and pickup are you running and how does that compare with what others with 460s are running? (I have an FE, so can't really comment on what works, doesn't, but something to consider).

I have a Canton Road Race Pan and the Kasse Oil Pump. No problems - works great.

STL Mark,

Oh oh... :eek:

I have the Canton 460 "Road Race" pan also. In a word, it doesn't work. I know one other Cobra owner who used the same pan on a 460 and had the same exact problems.

The pan is likely OK for gentle street driving. If you corner spiritedly, even on the street, it stinks - the oil pressure drops to zero or thereabouts. I discovered this first at a small track and then at Sebring - on right turns more often it would lose pressure. Nothing helped. I took the pan off multiple times, checked the operation of the trap doors, checked and re-checked the pickup-to-pan clearance and everything else I and Canton could think of.

Bottom line: the Canton "Road Race" pan for the 460 does not work. Possibly another brand, say Aviaid, Armando or other brands may work, but this one does not. I wish I'd tried one of them instead.

Solution? Accusump. Guess who makes it? Right, Canton. Wonder why?

Anyway that's the only solution for track use I know of so far. It's also great for pre-oiling if the car sits for a month or so between starts as happens occasionally with mine. I'm still watching the Kaase thread but with less optimism as time goes by since I don't have another 6" of ground clearance to work with.

Let us know if there re other possibilities!

Tom

Thanks! This is some great information. We still havnt got to the bottom of it yet. My builder is in ohio and i am in ny to make it worse i have a broken leg. so i need help and other peoples time. Anyway we are eliminating the small stuff (crossed oil lines on remote filter, the filter itself, pressure guage) We cut the filter open to ensure that we didnt suck something into the pick up causing restriction.

I think this is coming to a head. We used a brand new pick up on this motor, first time he used this type of pick up. (this is the only change made from the original motor). I was suspect of the new pick up from the beginning. The Kaase post leads me further down that path. The original pick up broke off which caused my motor to blow. That is why it was changed with another. I will pass this info to my builder as the fix may be to change the pickup or the pan. The 8 QT canton that I have takes up every inch of space, not sure that it can handle a larger pan?? I dont know the exact style of pick up used.

Thanks again for the info, I will be sure to report back on the solution.

Does an accusump eliminate the oil pump/pick up process all toghether? Im a bit of a novice and dont have a full understanding of how it works.

CBattaglia,

An Accusump is a very simple accumulator. It is a piston inside a tube about 4" diameter. One end of the tube is solidly closed and can be pressurized with air.

The small air pocket provides force on the piston to move the oil into the engine block. On a 460 there's an entrance to the oiling system just above and behind the mechanical fuel pump location, toward the front of the cam chain cover on the driver's side. Others have suggested using the gauge port at the top rear of the block but I have not tried this location.

The Accusump is pressurized by the oil pump when the engine is running, and if the engine oil pressure drops, the Accusump's pressurized air pocket forces oil into the engine's oil passage.

The capacity of the Accusump is one, two or three quarts - I use the three quart size on my 460s.

There's a valve located between the Accusump and the engine that needs to be opened after the engine starts (or just before starting the engine if pre-oiling is desired) and needs to be closed before the engine stops to prevent all the oil from being moved from the Accusump into the engine.

The valve can be a simple ball valve, or an electric pressure switch and solenoid valve combo depending on your preference. I have used both methods (on different engines).

There's a pretty nice explanation of this at http://www.accusump.com/accusump_tech.html

Hope this helps,

Tom

I'm not saying this is your cause but one you might want to rule out. For several years my car showed low oil pressure and was very unresponsive to RPM gains. It would always seem to fade. I was always chasing this and changing that to resolve it. One day I had what is called a lightbulb moment and decided to run a bigger gauge wire with new crimp on teminals from the sender to the gauge. Bingo! I had great pressure and now the pressure responded to RPM changes. I ended up swithing to a mech. gauge anyway but if your running elect. you might double check your wiring. Good luck!

John

I have a 429 and experiencing the same issues under load. At a stop with no motion I can rev. it up all day long and the oil pressure increases with the RPM. Once steady driving like on the highway no problem either. When I accelerate or go into a corner the oil pressure will drop from about 50 PSI to about 20 PSI. I have put my problem down to the fact that I have a modified front sump oil pan. When I built the engine I shorten the sump by 2" and lengthen the sump to maintain volume and put in a baffle gate to stop oil flow from the pickup. I don't think it worked. When I get on it a little or go around a corner I think the oil slops away from the pickup or gets foamy which may be the cause of the drop in pressure. I am hoping by putting in a rear sump pan (Canton Road Race) it will correct the problem. I am getting nervous when I read this thread, time will tell.

This was definately on my radar. My gauge is mechanical.

Call Kasse. He is "the man" when it comes to these 385 series engines. His pump will easily support your build. With his pump, my oil pressure is about 80+ on cold start up. Runs at 65 when warm and under load, and 45 at warm idle. Rock solid the whole time. My stock Ford pump used to dip to 15 or 20 at warm idle - not good. I have tracked my car before and driven it to the limit several times and have never had a problem with dropping pressure as described. For the pan, I'm sure there's better pans out there, but I doubt there's a better pump for these engines. As for Accusump, always a nice addition if you have the room. A great safety feature in case of a failure.

But, don't believe me - call the man himself.