Leave the oil system stock or modify

Which drivetrain to choose, so many choices, 4-cyl? 6-cyl? NA? Turbo?
Midlana1
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Leave the oil system stock or modify

Postby Midlana1 » 30 Jun 2016, 08:38

If you're building a cruiser, you can ignore this -

Short answer:
Research your engine's likelihood of having problems and expect to probably need to modify the oil system.

Long answer:
On the Locost site someone built an Atom-esque car using a Honda FWD drivetrain mounted mid-engine like Midlana. He's been driving it for about a year, gradually working out the bugs and building up speed. He recently posted "Pretty sure the engine's toast again."

Put an OEM drivetrain in a lightweight sports car and it will very likely have oiling issues due to the higher cornering Gs. For example, my Honda K20/K24 has a known issue where in hard left turns, oil runs to the front crank pulley and cam timing chain. The timing chain acts like a conveyor belt, lifting enough oil up out of the pan that the pump sucks air. If it happens a little, the driver feels power drop off due to the engine dropping out of VTEC (which uses oil pressure to switch cams). If it happens a lot, the engine's destroyed.

The builder's mechanic found the oil pump in good condition but the main bearings were blue (a sure sign of oil starvation). It's puzzling how builders can use engines with known issues yet think it doesn't apply to them (kind of like "If I think happy thoughts hard enough everything will be fine"). It puzzles me more how after such a failure, the builder decides it was just a bad engine and replaces it with another, somehow thinking the physics of the oil system on the new (identical) engine won't be the same. The bottom line is to research how your drivetrain handles high G load and the best place to find that is on forums dedicated to your particular engine. A simpler way might be to Google "Your engine + oil starvation" and see what pops out. Various solutions range from adding an extra quart, adding baffles, an Accusump, or a dry sump system.

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Re: Leave the oil system stock or modify

Postby Midlana1 » 07 Jan 2018, 10:05

I posted this on another forum and though it might be good to have here. This is in regards to using an Accusump to solve oiling problems caused by the stock pan allowing air bubbles into the oil pump in hard corners.

And then there's the Accusump. For those who don't know what it is, think of a rubber balloon connected to the oil system. When the engine starts, oil pressure inflates the balloon until equilibrium is reached. If at any time oil pressure drops, the balloon pushes oil back into the oil system to maintain pressure - that's pretty much it in a nutshell. I had one but got rid of it, and to explain why, well...

The mechanical shutoff valve on the Accusump should be used for better flow, reliability, and lower cost. The problem is that you *will* forget to open it before starting the engine, losing the "pre-oiling" feature. That in itself isn't a fault of the product, it's just something you have to remember before heading out on-track. Likewise, when you come in off-track and shut everything off, you *will* forget to close the valve first, 2-3 qts of oil get pushed back into the system when you kill ignition. That's harmless but it means when you go to start the car, you again don't get the pre-oiling feature, and have 2-3 extra qts of oil flaying around until you open the valve and the Accusump charges. Again, it's not really the product's fault but is, again, something you have to remember to do. There's that, and then there's something someone told me that ate at me until I decided it was a real problem. Disclaimer: This is only a theory of mine which may not be completely true, but I've fully bought into it.

The theory is that there are problems with using an Accusump and assuming it's fixed the oil supply problem. The problems are all related to how oil in a traditional oil pan takes on the consistency of chocolate milk when the engine's running hard due to air getting whipped into it, sometimes a lot of air. So you head out on-track and really start leaning on the engine. As you probably know, the crank doesn't actually touch the bearings, it's floating on a layer of oil, and that's great, until it isn't. The problem is that when on-track and at high rpm, oil viscosity drops way off and the high rpm "stirs" a tremendous amount of air into the oil, sometimes as much as 50%. This means that the "wedge" of oil keeping the crank away from the bearings is no longer 100% oil, but is maybe as low as 50% oil. This effectively cuts the viscosity in half again because the air compresses easily in comparison with the oil, and means the crank is riding dangerously close to the bearings. Unfortunately, the oil pressure gauge is no help because 60 psi oil pressure reads the same as 60 psi air pressure. Additionally, the Accusump can't help because the air/oil emulsion is at the same pressure as the oil in the reserve tank, so the Accusump doesn't push any oil back into the system.

Another situation: You're cornering hard when the above is going on and oil sloshes to one side of the pan, allowing the oil pump to suck in larger bubbles. Because it's only a brief interruption, the bubbles are followed by more oil, so the bubbles gets compressed along with it. In this situation you're right back to the above, having 60-psi air bubbles in your 60-psi oil, so again, the Accusump doesn't get involved, the oil pressure gauge continues to read normally, but the supply of oil to the bearings is now interspersed with larger bubbles, further worsening the oil situation.

So during the hard corner, the pump finally sucks in enough air that it looses prime and pressure drops off. If this is the first time it's happened, the Accusump works as designed and pushes fresh oil into the system to prop up pressure. But suppose this is the second, fifth, or tenth time it's happened on-track. When pressure is regained after the corner, the oil pump dutifully recharges the Accusump - with an air/oil froth. Have that happen a few times and now the Accusump ends up holding a 60-psi oil/air milkshake, ready to be pushed back into the system. Is it better than nothing, yes, but just.

Related to the above, air takes a long time to separate out from oil. In a dry sump tank, the returning oil is fed in tangentially such that it swirls around the wall of the tank, imposing high G-forces on the mixture. The force de-aerates the oil far faster than it does sitting still in an oil pan or Accusump. In the case of the Accusump there's another potential problem, that if and when the air does separate out from the oil, where does it go? It stays in the Accusump, pressurized to 60-psi just like the oil, ready to be fed back into the engine the next time pressure drops. If the Accusump is oriented with the outlet upward, that big air bubble is going to be the first thing into the oil system. If the tank is oriented with the outlet downward, the air remains trapped within the tank, meaning it'll get pushed out last. This is a problem that worsens over time because as the air continues to "off-gas", it forms a bigger and bigger bubble at the top of the tank. After a while, the "2-3" quart Accusump may contain maybe 1 quart of oil and 2 qts of air.

In addition to all the above, consider the case of coming out of a turn where the Accusump had to "dump its load". In this situation, the OEM oil pump is not only being asked to continue supplying full oil pressure to the engine, but also refill the Accusump reservoir. Whether the OEM pump has the capacity to supply oil to both at the same time will be case specific.

In conclusion, I feel that in the case of the oil system, you really do get what you pay for. The harder you run the engine and the more G forces it sees, the more a dry sump becomes a requirement and not an option. As said above, this is only a working theory of mine that I've "decided" is true without doing any testing with an Accusump. If someone uses an Accusump to fix a known oiling problem and, during a routine engine rebuild, finds no bearing issues, I'll reconsider my theory.

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Re: Leave the oil system stock or modify

Postby rennkafer » 07 Jan 2018, 16:50

That is exactly why we wouldn't even consider putting an Accusump on a race car at the shop I worked at. If you're working the engine hard enough that aeration or starvation is an issue, the only way to fix it is with a properly designed dry sump setup. The only road race cars that don't have them are those that are constrained by rules, and those where the engine/owner are too cheap to do it right. The latter are generally the ones you see off to the side of the track halfway through a race.
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