Our Subaru Boxer engines have a design limitation that most other engine designs don’t have: cylinder head drain-backs that are very closely in line with the engine’s oil level in the oil pan. The problem we face is that during hard cornering, oil starts to leave the pan as early as 0.67 lateral g’s. That oil has to go somewhere and that somewhere is back up into the cylinder head drain ports and on into the cylinder heads. At around 1.1 – 1.3 g’s, a sustained 4 second turn can completely fill up the cylinder head, thus putting enormous pressure on the pcv system and allowing the possibility of it sucking liquid oil back into the intake system. Very bad, indeed. This is largely why catch cans and AOS’s fill up so quickly on hard-driven track cars. To make matters worse, oil that is slammed into the cylinder head is not available for circulation through the oil pickup tube which can lead to un-porting of the oil pickup, and thus can quickly lead to engine failure. My neighbor, a former IndyCar and Daytona Prototype fabricator, and myself decided to put our heads together and see if we could address this situation.
Here are results of our quest to keep the engine oil in our oil pans and out of the cylinder heads.
Firstly, there is a direct correlation between g-loading in the horizontal plane and a liquid’s angle relative to that horizontal plane. There exists a mathematical equation, but the easy way is to use the tangent and inverse tangent (Arctangent) buttons on any scientific calculator. If you want to know what the angle of the oil in your pan is when you’re pulling g’s, insert that g number then press the arctangent button (tangent to the minus 1 power, usually found on the second level of most scientific calculators). For example, if you’re pulling 1 g, the oil level in your pan will be at a 45 degree angle to the horizontal. Makes sense, since you have 1 g pulling downward from gravity and 1 g pulling the oil sideways from cornering loads. If you’re pulling 1.25 g’s, then the angle would be around 51 degrees and 2 lateral g’s would be about 63 degrees. If you want to know what simulated g a given liquid angle would represent, just enter the angle and press tangent. Remember, oil starts leaving the pan and starts flowing back towards the cylinder heads with just a 34 degree (.67 g) angle. Repeated right and left-hand turns of 1.0 g would have about 1 quart of oil in continual transit between the cylinder heads and unavailable for use through the pickup tube.
We acknowledge that anyone who is pulling consistent, sustained g’s in excess of 1.5 should probably be using a dry sump system, but for most of us who might have spikes of 1.2 – 1.6 g’s, this plate will keep the majority of the oil in the pan, available to the oil pickup tube and out of the cylinder heads. During hard cornering, not only is oil leaving the pan but the descending, 70% of oil returning from the main bearing and rod bearing areas is also subject to those g forces and is forced to go sideways back to the heads before it can return to the oil pan. The vertical block-off portions of the ArcTangent Design Oil Control Plate stop this flow and force it back down into the pan. This plate will also provide added protection from oil leaving the pan during hard braking and acceleration, but those areas have not been tested nor has any data been collected.
Competitor’s plates and baffles have rubber parts which must be periodically replaced and/or do not address the sealing off of the boxed-in areas at the oil pickup’s legs, where oil can quickly leave the pan before 1.0 lateral g.
The ArcTangent Oil Control Plate has no moving parts, can flow over 1.5 quarts per second of cold oil back to the pan and can keep the vast majority of oil in the pan past 1.5 g’s during hard cornering.