|The MGA With An Attitude
OIL STARVATION, Slosh, Baffles, and Accusump - OF-202
At 12:36 AM 6/21/2007 -0400, James Nazarian wrote:
"My BGT V8 is mostly an autocross car. Unfortunately, during autocross, I'm uncovering the oil pickup and starving the engine for oil."
Been there, but in my case it was cavitation of the oil pump at 7000 rpm.
"I'm trying to find information about wet sump oil systems for high performance engines. I'm not opposed to building an oil pan, I just want to know what to build. .... I'm considering an Accusump, but I'd like to solve the root cause first."
A car running on race tires can generate up to 1g of side force in a fast turn. For gravity return oil flow this is equivalent to tilting the car 45 degrees to one side while the engine is running at high speed. Naturally oil will flow to one side of the sump, so the sump needs to be deep and narrow.
Oil flow rate is quite high. In the Austin B-series 3-main engine (for example) the oil pump displaces 1/2 fluid ounce of oil per revolution. That works out to 54 quarts per minute at 7000 rpm, or nearly 1 quart per second. An engine in good condition only needs about 12 quarts per minute to reach relief pressure (at less than 2000 rpm), after which all excess flow (most of the oil flow) goes past the relief valve returning directly to the sump.
The pressure relief return port is at the LR corner of the sump. As such, articulated baffles might help to retain oil near the pickup screen during a left hand turn, but may do nothing to help during a right hand turn. The amount of oil trapped between the baffles may last 2 seconds or less before the center of the sump is sucked dry. It could help to pipe the relief return port over to the center of the sump in conjunction with baffles, but you then need to assure that the baffles are not so tall as to raise oil level in the center of the sump high enough to touch the whirling connecting rods.
It is more effective to make the oil pan narrow and an inch deeper and extend the pick-up pipe an inch to lower the pick-up screen. If the sump extends below the frame, then speed bumps become a hazard.
A windage tray might be used to reduce foaming of the oil, but does nothing to help the sump slosh problem.
An Accusump unit that can retain one quart of oil can supply oil to the engine for up to 5 seconds in the event of pick-up starvation. The Accusump maximum pressure must be set slightly below the setting of the pressure relief valve so it will charge up from normal oil pump delivery and will not dump its contents past the relief valve. Or in simpler terms, the Accusump cannot charge to a pressure higher than the pressure relief setting, so limiting the Accusump pressure rating in that range will allow full charge in the Accusump reservoir.
A single hard turn lasting more than 5 seconds would be rare for an autocross car. However, consecutive left and right hard turns with very little transition time in between (like a long slalom for instance) could do you in. For oil starvation conditions lasting more than five seconds, the "standard" solution is a shallow oil pan, dry sump, scavenger pump, and external oil reservoir. This gives the possibility of having a deep narrow sump (external reservoir) without extending the oil pan near the ground.