Originally Posted by boatmonkey82
gm 383 eagle forged crank h-beam rod ect if i remember i used a high pressure melling pump with 15-40 oil , all has been fine till now . The oil level is good but at high rpms the oil pressure gets up to 60-70 then starts to fluctuate and start dropping if i stay in it . bypass ? arreation? bad oil pump ?
the main issues i have had with this motor is after about the first 3k i left the light pouring the coals to it and the lower crank gear shattered , yes it was billet , yes it bent a intake valve . fixed all of that and had a arp head stud fill the oil up with water fixed that and have driven say 5-6k since and now this problem. I am very hard on this motor hence why i spent too much on the bottom end to have this happen . the oil pan is aluminum pro comp finned deal with no trays or baffels .
Lets move to the pan, it needs trays and baffles, it doesn't need fins nor aluminum, leave that stuff for the East LA low riders.
50 to 70 PSI at WOT is fine it's the eventual lowering that's saying something isn't right.
At high RPMs a lot of oil becomes entrained with the crankshaft. Windage trays and crank scrapers help get it out of the crank's spinning influence and back into the pan. Also, the process of pumping this oil like mad then draining back through all that spinning hardware mixes a lot of air into the oil. Moussed oil is of little use to the engine while being hard to pump. There needs to be enough oil in terms of pan capacity that it gets a moment to relax and let the air out.
Baffles are needed to keep the oil by the pump pick up and out of the crank. A simple one mounts on the rear main, it is intended to keep acceleration forces from driving oil up the back of the pan into that big counterweight on the end of the shaft. Other baffles on the pan floor are intended to keep the oil from racing away from the pick up.
The pick up needs to be about 3/16ths to 3/8ths of an inch from the bottom of the pan. This keeps the engressing oil from developing a vortex that allows air to be sucked into the pump along with the oil. This is achieved with an extended pick up or better yet with a lowered pump position. Frequent high RPMS should use a 5/8ths inch pickup tube instead of the the more typical 1/2 inch pipe. If you push on an engine hard, even on the street, the pan should have a capacity of at least 7 quarts. The use of a cooler should be considered, hard driving runs the oil temps up really quick, especially when followed by slowing or idling the engine after hard blasts or long periods of high output.
Non of this is to say thet you analysis of potential problems isn't good, these are problems often seen. High output pumps move a lot of oil, or try too. If the clearances are set to typical race values then the leakage rate through the bearing is high making for a lot of oil flying around in the engine but more or less average pressure will be seen on the gauge. If the clearances are tighter as typical OEM spec, the pump has a harder time shoving that much oil through the clearance which then shows as high pressure where the relief spring open the pressure vent. In a situation like this a lot of oil can be vented which in a typical Chevy pump is back to the inlet side of the pump, never having seen the pan. This makes the oil get really hot and is known to disturb the intake flow and it contributes to pump chatter because the incoming oil now has a frequency modulated onto it which is the same as the pumps rotation frequency. Tricky stuff!