Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

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nicholastanguma
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Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by nicholastanguma »

Time for another bench racing engineering question.

If using a good oil cooler and giant cooling fins on the jug itself how small could an air cooled engine's oil capacity safely be?

For example: 1.5 liters for a 500cc single cylinder? 1.0 liter for a 350cc single cylinder? 1.0 liter for 250cc? You get the idea.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by oldjohnno »

This question sometimes comes up in hydraulics, and one of the main considerations is aeration. A small capacity means a very short residence period in the tank, leaving very little time for the air to leave the oil. In an engine you'd have to consider whether it would survive on a diet of aerated oil and/or whether you'd have to take additional steps to deal with it. Dilution/contamination might also be an issue, depending on the race duration.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by nicholastanguma »

oldjohnno wrote: Sat Sep 18, 2021 1:34 am This question sometimes comes up in hydraulics, and one of the main considerations is aeration. A small capacity means a very short residence period in the tank, leaving very little time for the air to leave the oil. In an engine you'd have to consider whether it would survive on a diet of aerated oil and/or whether you'd have to take additional steps to deal with it. Dilution/contamination might also be an issue, depending on the race duration.

The air cooled, 4 valve Husqvarna 510 from the 80's was a four stroke thumper that used a mere ONE PINT of oil for the entire engine. It was known as a hot temp engine, but according to Super Hunky himself was of anvil reliability. There's some kind of voodoo engineering they were employing, I think.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by oldjohnno »

I'm guessing the Husky used rolling element bearings in the bottom end at least - common with 4T singles - and this eases the oil requirements greatly. Stihl took this to its logical conclusion with its 4-Mix four strokes and virtually eliminated the oiling system by using two-stroke style premix to lubricate the entire engine https://youtu.be/8JPwXoQIWFs
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by RDY4WAR »

Aeration will be more and more of an issue the lower in capacity you go. The oil's specific heat and viscosity plays a factor as well. As you go lower in capacity, going lower in viscosity combats the two issues above, but also needs very good base oils that are thermal and shear stable, excellent anti-foaming additives, and as low of a friction coefficient as possible. Even then, I don't like it.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by Ken_Parkman »

Residence time is also a function of oil flow pumped through the engine. If it a small oil flow engine (small clearances or leakages) you have better residence time and can get away with smaller oil capacity. Large flows and small capacity is a bad combo.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by Kevin Johnson »

nicholastanguma wrote: Sat Sep 18, 2021 5:57 am ...


The air cooled, 4 valve Husqvarna 510 from the 80's was a four stroke thumper that used a mere ONE PINT of oil for the entire engine. It was known as a hot temp engine, but according to Super Hunky himself was of anvil reliability. There's some kind of voodoo engineering they were employing, I think.
Are you sure about the capacity? The figure that I am seeing discussed is 1.8 litres (10w40 circa 1983 specs). That is a dramatic difference: 1 pint is ~ 473ml or not quite 25% of 1800ml (1.8 litres).
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by nicholastanguma »

Kevin Johnson wrote: Sat Sep 18, 2021 10:19 am

Are you sure about the capacity? The figure that I am seeing discussed is 1.8 litres (10w40 circa 1983 specs). That is a dramatic difference: 1 pint is ~ 473ml or not quite 25% of 1800ml (1.8 litres).

Source here: http://articles.superhunky.com/4/294
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by Kevin Johnson »

nicholastanguma wrote: Sat Sep 18, 2021 4:53 pm
Kevin Johnson wrote: Sat Sep 18, 2021 10:19 am

Are you sure about the capacity? The figure that I am seeing discussed is 1.8 litres (10w40 circa 1983 specs). That is a dramatic difference: 1 pint is ~ 473ml or not quite 25% of 1800ml (1.8 litres).

Source here: http://articles.superhunky.com/4/294
Source here: https://forum.ozvmx.com/index.php?topic=25049.0

In your reference, the one pint refers to the volume of the reservoir [top-end cam case] that is available/adjacent to the reed valves pumping system. That is different from the total volume of oil available to the engine and to replenish the top-end cam case.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by nicholastanguma »

Kevin Johnson wrote: Sat Sep 18, 2021 5:25 pm
nicholastanguma wrote: Sat Sep 18, 2021 4:53 pm
Kevin Johnson wrote: Sat Sep 18, 2021 10:19 am

Are you sure about the capacity? The figure that I am seeing discussed is 1.8 litres (10w40 circa 1983 specs). That is a dramatic difference: 1 pint is ~ 473ml or not quite 25% of 1800ml (1.8 litres).

Source here: http://articles.superhunky.com/4/294
Source here: https://forum.ozvmx.com/index.php?topic=25049.0

In your reference, the one pint refers to the volume of the reservoir [top-end cam case] that is available/adjacent to the reed valves pumping system. That is different from the total volume of oil available to the engine and to replenish the top-end cam case.

Thank you for the clarification.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by Momus »

Modern watercooled 450 cc MX bikes with well over 60 hp at the crank do fine on about 1200 cc of oil with no external oil cooler.

Aeration is not really a factor with all roller bike engines.

Air cooled Hondas I play with use a small gear rotor pump and at operating temperature run at less than 5 psi.
I run a full flow oil cooler on some of these- they are making several times standard output and being raced, and have zero trouble with oil degradation.

Sometimes slow work around torque peak is the most cooling demanding.
I'd be doing some testing with temp labels or a capillary guage to get real world information.


Earlier Honda 250 MX bikes ran as little as 650cc reliably; provided of course the level was maintained.
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by nicholastanguma »

Momus wrote: Sun Sep 19, 2021 8:42 am Modern watercooled 450 cc MX bikes with well over 60 hp at the crank do fine on about 1200 cc of oil with no external oil cooler.

Aeration is not really a factor with all roller bike engines.

Air cooled Hondas I play with use a small gear rotor pump and at operating temperature run at less than 5 psi.
I run a full flow oil cooler on some of these- they are making several times standard output and being raced, and have zero trouble with oil degradation.

Sometimes slow work around torque peak is the most cooling demanding.
I'd be doing some testing with temp labels or a capillary guage to get real world information.


Earlier Honda 250 MX bikes ran as little as 650cc reliably; provided of course the level was maintained.

Thank you for your help!


Momus wrote: Sun Sep 19, 2021 8:42 am Aeration is not really a factor with all roller bike engines.
Do you mean bike engines equipped with all roller bearings?
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Re: Does Small Oil Capacity Matter If You Have A Lot Of Oil Cooling??

Post by Momus »

nicholastanguma wrote: Sun Sep 19, 2021 5:55 pm
Momus wrote: Sun Sep 19, 2021 8:42 am Modern watercooled 450 cc MX bikes with well over 60 hp at the crank do fine on about 1200 cc of oil with no external oil cooler.

Aeration is not really a factor with all roller bike engines.

Air cooled Hondas I play with use a small gear rotor pump and at operating temperature run at less than 5 psi.
I run a full flow oil cooler on some of these- they are making several times standard output and being raced, and have zero trouble with oil degradation.

Sometimes slow work around torque peak is the most cooling demanding.
I'd be doing some testing with temp labels or a capillary guage to get real world information.


Earlier Honda 250 MX bikes ran as little as 650cc reliably; provided of course the level was maintained.

Thank you for your help!


Momus wrote: Sun Sep 19, 2021 8:42 am Aeration is not really a factor with all roller bike engines.
Do you mean bike engines equipped with all roller bearings?
Yes, that is what I mean. All roller is probably a little inaccurate as gear shaft journals, mesh etc are 'plain'.
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