I have been experiencing oil pressure problems above 4000 rpm which seems to be a relativly common problem on some rebuilt motors. I contacted Nick at Nutek and he told me that they run a lot of stock pans with Melling pumps with no problems. He did tell me that the Melling pumps they install on LT1s are M1055 not the M55 (which is what I have). He told me the M55 pump has a larger diameter but he honestly did not know why it would cause a problem. He also told me to make sure the pickup height is correct.

Well the pan is off and I checked the height of the Melling pumps pick-up and it was about 1 inch off the bottom of the pan. I installed a new blueprinted OEM pump (white spring) and its pick-up is currently sitting about .825" off the bottom of the pan at the mouth of the pick up and about .650" at the rear (see the photos of the clay Clay1 Clay2 ). Nick said that he sets them up so the pickup is .250" - .375" off the bottom of the pan. I am guessing that I need to drop this pickup almost .400" to get it set right. Is this the correct height and does anyone else have any experience setting the pick-up height?

 

Depnding on whom you talk to, 1/4" - 1/2" is the range. I prefer something a little closer to the min. I set mine 1/4" - 3/8". So, yes, what you've got, is excessive.

 

I agree with Arnie

 

Just out curiosity why does that make a difference? Isnt it basically filled past the neck of the pick up so no matter what its full either way? Is it a suction thing?

 

A problem develops when there is extreme braking, acceleration, or cornering forces that cause the oil to 'climb' the pan wall. It is not unusual to have the oil 'glued' to the wall at a 45* angle in extreme instances. When this happens during high rpm use, which implies there may be a couple of quarts of oil in drainback mode (not back in pan as yet) it becomes easier to understand the pickup could realistically end up sucking air in lieu of oil.

With a pan having the correct, (read effective) baffling in place, and a pickup reasonably close to floor of pan, (an effective/concerted oil drainback plan and pulling no more oil out of the pan than what the engine really needs, doesn't hurt) the likelihood of the pickup sucking air is greatly diminished.