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 equivelant to tilting
the car 45 degrees to one side while the engine is running at high
speed. Naturlly 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 cubic inch 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 hazzard.
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.
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 without extending the oil
pan near the ground.
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