Oil Accumulator
 

I am by no means an expert on this subject, but I have tried to exercise due diligence. I installed a 2qt accumulator on my car as per instruction from Element Tuning on my initial engine build. As it is now, I have a manual valve that I open when I go on track and close when I come off. Most of the time I actually remember to do this. (It's an item on my check list).

My car is na. Tein coilovers, 200tw tires. I run DE2 now but plan to move to DE 3 later this season. My car pulled 197 hp and 163 ft lbs on PTuning's dyno. My primary tracks are VIR and Summit Point.

Recently, I have read the comments in the Gen 2 section that call into question the benefit of accumulators. With that in mind, I contacted Phil Grabow and had a bit of a discussion. He was very generous with his time and expertise. Based on his testing and experience, he recommends using the accumulator and using it without a low pressure switch. He described it as a poor man's dry sump.

Here's my set up.

What pressure do you have it set at?

Can he share the before/after data?

Calling it a poor man's dry sump is misleading. A poor man's dry sump would be a 2-stage pumping back into the sump (like on the newer 911 Carrera) vs a proper 5-stage with a remote reservoir (911 GT cars).

This is a manual setup, there is no valve. On track it's open all the time.

I thought you still had to set a precharge pressure.

The 'spring' pressure that returns the oil, needs to be charged with air, but that is a set once and forget. Essentially, it's the spring on the other side of the accumulator's plunger.

With how BLSFRS is running it, it's open. This is more like a dampener that takes down high rapid spikes and low rapid drops. So if you are in a condition and your pressure goes from 60psi to 2psi, the plunger will start pushing oil back, at 60psi. Of course, as the conditions continues beyond a microsecond and the accumulator piston starts to move, it's pressure drops. Just as an example say you have that 2psi for 5 seconds, at 0 seconds, it's 60psi in the accusump, and 1 second elapsed it may be 40psi, and 2 seconds, 20psi. You can actually calculate how much oil the accumulator holds and what the time/pressure output plot looks like. Once we have flow data, you can make some rough worst case calculations.

With an electronically valved setup, you can fill the accumulator at your peak pressure (or whatever peak pressure you set it to) and then set a minimum value, where the accumulator backflows into the oiling system, say if it dropped below 40. This method gives a bigger pressure delta, which means the accumulator has more volume of oil to push when there is a pressure drop. Plus, it won't continuously recharge, it only recharges once you're over a preset value.

I had been running a precharge of 7psi as recommended by Canton. Phil recommended 12psi.

I see part of Killer B's point, except that an open valve should prevent significant oil pressure drops by constantly feeding oil to the system. This does have and end point but, hopefully, by that time, you are out of the situation that caused the oil to slosh away from your pickup and your engine can start sucking oil again.

A problem that I see with running an electronic valve is that the accusump opens only when the engine has reached a preset low pressure. As Killer B stated there is a bigger delta so there is a bigger discharge and bigger recovery that takes oil away from the engine.

Phil might have specific data to back up his recommendations but I suspect that he did things to prevent his engines from going boom.

I think that we all know that the Accsump is not a completely perfect solution but it's a lot cheaper than a dry sump.

You can get a switch activated electric valve instead of the lever. Still operates the as strictly open or closed (although it will allow recharge when closed, unlike the manual lever), but doesn’t require mounting and routing a push/pull cable.

Electric valve also allows for getting fancy with computer integration to vary opening threshold according to conditions.

One of these days I should really do something with the accumulator I’ve had sitting in my basement for like 13 years.

I tried 3 electronic valves. One (from Canton) burnt out and 2 (from Moroso) leaked.

Thanks, I was wondering since I had seen people on other platforms recommend a wide range, from 5-25psi, which is well beyond the range Canton recommends. So I was curious what you were running and how you settled on the number.

Would be interesting to see how much oil goes into it when it's charged. Would be easy for the pope since he has one sitting in the basement.

P1V1=P2V2 anyone? Oh Boyle!!!

That’s some bad luck. My valve is from Moroso and ran on a car for 7 years without issue.

Well I have a 2 qt on the way. I'll source the valve and hose separately. Not sure why I haven't gone this route before, I had looked into it before but don't know why I didn't follow through.

I am so thankful I don't go to tracks and my worries are extremely simple comparatively Props to all of you for fighting hard

If you're willing and able to do some pressure/volume testing shoot me a PM, and I can walk you through a couple of different methods to do that.

When I get to that point I will let you know. Engine still has to come out of the car before this season starts :sigh:

@blsfrs

To the oil galley, are you using an 18x1.5 to -10an adaptor or something else? Like a 18 x 1.5 to 1/2npt then to -10


edit:Nvm found a -10 adaptor straight to the oil galley. Still curious what you are running though.

The first option: 18x1.5 to 10an adaptor. Don't ask me where I got it 'cause that was 3 years ago and I can hardly remember what I had for breakfast.

lol

Thanks. That is exactly what I got on order. Have all the hose and fittings on the way.

Thinking about just buying something like this to operate it. It is a solid core wire so it works in push/pull, and it's like 100 cheaper then Canton's manual cable kit.

https://www.amazon.com/Dorman-55198-..._t3_B0BC87YL8R

That cable basically is the same one that I have. I ran mine through the "sound hole" just below the HVAC.

FWIW: If you mount your accusump in the same location as mine, it has to be far enough forward so it sits between the bars so the bottom of it should be flush with the bottom of braces. If it sits on top of them, it contacts the hood.

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.

That is good to know. I was checking out some options that are not going to work and am thinking about mounting it vertically.

I just got off the phone with Canton, their 2qt accumulator actually holds 2 quarts not 1.5. So 7x64/90=5oz of air volume and 59oz oil. I'm a licensed medical professional, so somebody needs to check my math.

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 :)

The system is incomplete. For an accumulator to do any good there must be some hysteresis, like an easily opened check valve to fill and in parallel, a dump valve that flops open below a set pressure delta.

I have been looking at adding a secondary dump for a couple days. I just hadn't decided where it would go.

I am not under any type of delusion that this is a fix. I consider it more a set of suspenders as I have already get dropouts into single digits and this year I will be on more tire and aero. I have to do something at this point.

I think this is where an electric valve and a controller would be beneficial rather than a manual valve or pressure switch.

The electric valves are only closed in one direction when off enabling it to fill and hold until switched on by the user or a pressure switch, unlike the the manual valve which must be opened to fill and/or empty.

Tying an electric valve into either a standalone or arduino (etc) and say comparing oil pressure vs rpm vs accumulator charge pressure to determine when to open the valve would give the benefit of fast reaction like a simple pressure switch, but without dumping oil every time pressure drops because rpm did.

Link?

All the solenoid valves I was looking at were either NO or NC so they won't fill unless triggered or would need a one way bypass to refill the accumulator. Most also had buna orings and seals so not good for high enough temperature. Need either viton or epdm.

I wasn't ready to build it. I'm keeping all options open until I feel that I've adequately defined the requirements. :D

I don’t have a link, but my Moroso valve only held against pressure in one direction when de-energized. As long as the “In” port faced the accumulator it could charge and hold when switched off. Made it convenient to fill before shutting off the vehicle. Also, essential for pressure switch activated systems to be able recharge once oil pump output resumes and the pressure switch turns off.

^ This!

With NO valves it's a dampener. With valves it's supplies supplemental pressure, but again, it's highly arguable as to the effectiveness on an FA, and not a solution to the core problem. We already know on EJs (with 12mm pump and D-AVCS it's not an effective solution.


On the right track here, but it should go a step further and ONLY recharge when load is low. With a good standalone, this is easy to do. Off the shelf, it will recharge, dropping system pressure, at the worst possible time, under full load.

Sorry to revive this thread...with a manual only valve set up, what happens if you spin out and stall?

I assume the oil pressure will go to 0 psi and overfill crank with 2qt of oil rapidly, since the driver will most likely not be able to close the valve quickly.

Electric valve would prevent this as long as it is getting power?

I doesn't hurt anything. I've forgotten to close mine after a session and have not had a problem. Maybe a little smoke on startup.

It's not quite 2 quarts. If you start with a 7psi precharge, at 60psi of engine oil pressure, the accusump with have 56.5 oz of oil in reserve. (If my math is correct LOL)

Also, the first half of the discharge is reasonably rapid. Discharge slows considerably as the pressure and volume in the accusump decreases.

I'm finally getting my FRS back together. I wanted to continue reading my OP at the top galley so I added a "tee fitting. So far, it works great.