The Subaru EG-33 engine is normally a "wet-sump" type engine - that system works fine for vehicles run on pavement but has proven to be less reliable in off-road conditions, leading to bearing failures.  In our pre-runner application, a "dry sump" oiling system is much preferred.  There are commercial "bolt-on" dry sump systems available but we already have the "expensive parts" on hand (they came ready for installation with the engine when we purchased it) so we're fabricating the remaining parts we need ourselves.  Essentially, we do away with the stock oil pump and oil pan in favor of a "dry sump" pump assembly that consists of both a scavenge (oil return) pump and an oil supply (pressure) pump.  The scavenge pump continuously returns the oil draining from the bearings to an external oil tank.  The oil tank feeds the input of the oil supply pump, insuring a steady supply of oil to the engine. 

Dry Sump crankcase plate being milled to shape
We eliminate the need for a stock oil pan; the oil supply will be contained in an external tank.  We still need to close the gaping hole that would otherwise exist when we remove the oil pan so this plate is needed to replace it.  Here, you see the sump plate being milled to shape.  Next, we'll drill the mounting holes and mill the "inside face" to direct the draining oil to the scavenge pump pick up fittings.

Sump Plate mounting holes drilled and counter-bored
This is the "outside" face of the sump plate; the two large holes near the center of the plate are where the scavenge pump hose fittings (one is visible in the upper left corner of this photo) will be welded in place. 

Sump Plate "inside" face milled to shape
We milled the inside face of the sump plate to help direct the draining oil towards the scavenge pump pick up fittings.  The scavenge pump will ensure that very little oil collects inside the engine - it will immediately be pumped to the external oil tank for use by the oil supply pump.  We provided two pick up fitting locations but we have only one scavenge pump circuit.  We'll use only one of the pick up fittings; once we determine which location works best, we'll make the pickup connection there and the other fitting will be capped. 

Scavenge Ports welded in place
Trevor welded these at home - it was a bit of a challenge with his garage 220V circuit breaker limiting the current he could apply...

Sump Plate temporarily installed to check the fit
It looks like a good fit - now we just have to etch and apply the Alodine "conversion" process then "final" install it.

 

Dry Sump Pump
This is the "dry sump" pump that replaces the stock oil pump.  It's an external pump "assembly" with two independent pumping sections on one shaft - one for "scavenging" oil from the crankcase and returning it to the external oil tank and the other for delivering oil from the storage tank to the engine under pressure.  The pump will be belt driven by the crankshaft via the extended shaft seen protruding from the plastic cover.

2-Stage oil pump disassembled for overhaul
The pump was missing seals and not correctly assembled when we received it with the engine core.  Trevor disassembled the pump, inspected it and replaced all the seals.  Fortunately, aside from the missing seals, it was in excellent condition.  Once reassembled and installed, Trevor operated the pump with a drill motor to verify function and check for leaks.  The pump was clearly working; the pressure lines "flexed" and the oil quantity in the tank dropped as all the new lines filled with oil. 

To perform an initial oil pressure adjustment, we again used a drill motor to simulate idle operation.  We noticed that the oil quantity in the tank didn't stay constant - oil was accumulating in the engine sump faster than it was being scavenged (the pressure pump is twice the size of the scavenge pump).  We installed an oil pressure test gage to see why that might be; we found the oil pressure was quite high, leading to the in/out flow imbalance.  Fortunately, pressure is easily adjusted via a bypass valve in the oil pump.  With the idle oil pressure adjusted to a "normal" range, the scavenge pump now keeps the engine sump "dry" as it should when we turn it with a drill motor.

With the engine running, we found that the scavenge oil pump works fine up to about 4000 RPM but beyond that point doesn't keep up with the amount of oil flowing into the pan from the bearings.  We believe that this is due to a "vortex" being formed directly above the oil pickup at high flow rates (high RPM's).  The vortex allows air to be entrained, reducing the scavenge pump's ability to keep up with the amount of oil flowing into the pan...  After researching the issue, we believe the solution is to incorporate "vortex breakers" into our oil pan.  They're essentially cover plates that only allow the oil to be drawn from around their perimeter rather than from directly above the oil pickup fittings.