Quote:
Originally Posted by pope
So, if I’m doing this right:
7*1.5=90*x
X=0.1166667
1.5-0.1166667=1.3833333
Then, when the air side is charged at 7psi and compressed to 90psi, by filling the oil side, the air chamber will reduced from 1.5qt to 0.1166667qt leaving 1.3833333qt of volume for the oil side.
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Keep in mind this is a static formula for that snapshot in time. With the unit run as an accumulator (dampener/open), it's constantly being supplied different pressure, based on RPM, AVCS, etc... plus flow rate is going to be based on the pressure differential, which is almost always going to be 7psi, unless there is an instant and dramatic loss in oil pressure.
The right way to do this is plot out the full travel and flow rate based on a specific condition, like instant pressure reduction from say 60psi to 40psi over say a 3 second period.
When RPMs are naturally varying as you are going through the gears, downshifting, AVCS, etc., the oil level in the accumulator is going to be constantly changing. Again, this can be plotted out so if you know in gear 4 at 5,000 RPMs if your pressure instantly goes from 50psi to 20psi and stays there for 5 seconds you can find the flow rate over those 5 seconds back into the system.
None of these scenarios come anywhere near dumping 1.5 quarts, and you're not charging with 90psi, because at temp pressures are never that high. Once you start looking at these flow rates, you see this is not going to prevent an engine from popping. Maybe it keeps it from popping today, or tomorrow, but it's not fixing a problem (if one exists). For anyone that wants to nerd out on this and actually plot it out, ideal maximum flow rate is going to be around 8 quarts/min (1.33 Quarts/10 seconds) for a Suby 12mm Gerotor pump. I don't know how close this is to actual, but is based on other Subaru engines of similar design, same gerotor pump size, and D-AVCS like the FA20/24. Should be a safe starting point.
Another wild card to add into the mix that no one ever thinks about is air in the system. If the pump or bypass is cavitating (providing an instant loss in pressure) your accumulator is going to be splitting duties between adding oil that is going out bearing clearances, and compressing the air that is now in the oiling system. Same deal if the pickup starves. Again, real world conditions are HIGHLY dynamic.
I stick by my opinion for now that accumulators are not a good application for these engines, or any Subaru engines. It's a dampener (when used open) on an engine that doesn't need one. It's more cost, complexity, potential leak points, and weight (worse, weight that's up high).
If anyone wants to put the time, effort, and risk in to proving me wrong, I'm game, and will gladly eat my words and humbly beg for the forum's forgiveness. We have the dyno and every bit of testing equipment to make it happen. Better yet, have Phil from Element post real data. He loves debating me, and we're way overdue
