High RPM Oil Pressure Drop.

[Josh Noser]

I have a 68 L-71 and I have the problem of a high RPM oil pressure drop. As I understand it the oil is getting trapped upstairs. I have the correct 6 quart oil pan. I read in the archives, from Duke I believe, that it is ok to run extra oil. Is this ok? If so how much. Also I am running 10 w30, is here a better weight oil to run?

Thanks for all the help!

[Mike Cobine]

Re: High RPM Oil Pressure Drop.

When racing these engines, like most engines, oil takes too long to drop back down. The most common method is polishing the insides and cleaning up the drain holes to promote drainback.

Usually, you can just ckeck the drainback areas in the heads and the ends of the lifter valley.

If you are running sustained high RPM, then I assume you are not doing the normal judging events, and so a few deviations from stock may be allowed. One is to use an Accusump, an oil accumulator that stores oil under pressure on an air spring that then pushes back into the oil system when pressure drops.

If you are actualy racing, then you should consider a dry sump system and an external oil tank.

Also, if you are racing, then you should consider 20W50 racing oil.

[Clem Z.]

Re: High RPM Oil Pressure Drop.

you are correct as the oil is not returning to the pan fast enought as i had this problem with my 66 425 HP 427 so i just ran it 1 quart over full.GM still recommends that you run 1 quart over full even on the new corvettes when doing "spirited driving" this is one disadvantage of the "piddle valve lifters" they use in BBC as they allow lots of oil upstairs. when we raced BBC engines we always used "edge orifice lifters" but we also used needle bearing roller rocker arms

[Josh Noser]

Re: High RPM Oil Pressure Drop.

I am not racing but this happens when I floor it and the engine revs ~5,000 or > RPM. I will check the oil return holes. The car is fairly original but I don't plan to have it judged but on the other hand I don't do any modifications that cannot be undone simply by reinsatlling the original part. The car is street driven but just mainly to cruise. Baised on that what is recomended I do to solve this problem? Also recomended oil?
Thanks,
Josh

[William C.]

Re: High RPM Oil Pressure Drop.

Clean the drain holes at the corners of the heads on the outboard sides, check to see if you have the correct dipstick, and check the pickup on the pump to make sure it is as low as possible in the sump.

[Josh Noser]

Re: High RPM Oil Pressure Drop.

Thanks Guys--I will check the return holes and run an extra quart of oil and see if that helps. I have the correct dipstick and it reads full when I put 6 quarts in.

[Mike Cobine]

Bill's right

It used to be very common for the pickup on the pump to get knocked up from the bottom of the pan, so tha tyou could have an inch or more of oil it couldn't get. And that inch can be critical.

Unless you can see the pickup through the drain hole, you will probably have to pull the pan and measure.

The pan is really easy to pull. Turn the steerign wheel to the right. Disconnect the idler arm on the right side frame. Have someone turn the steerign slowly left while you pull down on the steering linkage. Then you have plenty of room to remove the pan.

If the pickup has moved, you need to pin or weld it in place to prevent it from moving up or worse, falling out.

[Josh Noser]

[Clem Z.]

Re: High RPM Oil Pressure Drop.

are you sure you have the HI PER oil pan with the trap doors and the box around the pickup because the oil could be climing up the back of the pan on acceleration.

[Michael H.]

Re: High RPM Oil Pressure Drop.

I agree with Bill. I would suspect that your oil pickup screen is not installed correctly. It's very important that this be positioned correctly in the oil pan. These do have a habit of moving up and you wind up with the exact problem that you describe.

Michael

[William C.]

Re: High RPM Oil Pressure Drop.

If it runs to 70, it should hold 70 until you shift. Any falloff is a sign of pump starvation or cavitation.