Synthetic or Mineral Engine Oil for 2 Strokes?

jaguar

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#1
Often synthetic oils are compared to conventional mineral oils in cars which skews the results if you are a 2 stroke motorcycle rider considering which type of oil to use. That is because in a motorcycle using pre-mix the owner mixes in the oil with gasoline at different ratios but in a 4 stroke engine there is no mixing of oil with gas at different ratios. Of course the results would favor synthetics in 4 stroke engines but if a synthetic oil is twice as good as a mineral oil ounce per ounce then does it maintain any advantage if you use half as much as you would with a mineral oil? (50:1 compared to 25:1 gas/oil ratio) Keep this in mind, that 2 strokes have been proven to have more power the more oil is used, regardless of what type oil, because of better compression due to better ring sealing and less friction. They also are more combustible than true synthetics and so contribute to engine power. Mineral oils leave more top end carbon deposits and require more engine maintenance to clean off the head and piston top. They also create more smoke and leave more spooge (black gunk) in the exhaust pipe. That is their downside. Synthetic oils should be used in engines with exhaust power valves and in engines that won’t be taken apart often. also they have the clear advantage in 4 strokes since they break down at a slower rate (since the oil is “recycled” instead of being used temporarily in a 2 stroke). Another advantage of synthetics is they maintain more lubricity when there’s high heat or cold. Their oil is more stable with temperature variations. But with 2 stroke engines if you do frequent maintenance and want the best power then I would recommend any good oil made with the highest grade petroleum oil which is grade 3 oil. It is so good that legally it is allowed to be labeled as a synthetic oil. If you choose to use a true synthetic oil (PAO or ester) then I would recommend one made with the ester type oil which is better than the PAO type synthetic oil.
While group 4 synthetics are better than group 3 for high and low temperature (oxidation resistance & pour point) characteristics, group 3 synthetics have higher additive solubility. So which oils have group 3? Amalie Synplus has 82%. Maxima Scooter Pro is a blend of group 2+3 and true synthetic. Motul 510 2T has 25-50% group 3 and 10-25% group 2 oils. Fuel/Oil ratios I would recommend for an air cooled iron sleeved cylinder depend on max RPM:
engine oil___7K 9K 11K 13K RPM
SynPlus_____37 30 26 22
510_________29 24 20 17
Scooter Pro_24 20 17
If the cylinder inside is chromed (nikasil, etc) then just multiply any of the above ratios by 1.09
If the engine is water cooled then multiply by 1.1
 

jaguar

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#4
Which 2 stroke engine oils are the most slippery?
I had an idea to test synthetic vs mineral engine oil. By “mineral” I mean refined petroleum oil. I know that synthetics are thicker (and with less impurities) than mineral oil which is what allows them to be used at a thinner ratio. So I thought that maybe synthetics were also slicker. So I removed the cylinder and piston from my 100cc 2 stroke and tested how much grams pressure is needed to push the piston/rings thru the cylinder with different engine oils smeared onto the cylinder. The best oil was an ester type synthetic, the highest grade refined oil required 10% more pressure, the low grade refined oil required 16% more. So the synthetic won but not by huge margins. Reading up on oils I found one sight that said synthetics actually lagged behind the most refined petroleum oils in lubricity and needed additives to make them slicker. That is surprising to me.
 
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jaguar

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#6
Also Yamalube 2R has about 60% group 3 oil and most everyone loves it.

Here's a report I found on the internet about how more oil increases power:
"I have run Dyno tests on this subject. We used a Dynojet dynamometer, and used a fresh, broken in top-end for each test. We used specially calibrated jets to ensure the fuel flow was identical with each different ratio, and warmed the engine at 3000 rpm for 3 minutes before each run. Our tests were performed in the rpm range of 2500 to 9000 rpm, with the power peak of our test bike (a modified '86 YZ 250, mine) occurring at 8750 rpm. We tested at 76 degrees F, at 65% relative humidity. We started at 10:1, and went to 100:1. Our results showed that a two-stroke engine makes its best power at 18:1. Any more oil than that, and the engine ran poorly, because we didn't have any jets rich enough to compensate for that much oil in the fuel, and the burn-characteristics of the fuel with that much oil tended to be poor. The power loss from 18:1 to 32:1 was approximately 2 percent. The loss from 18:1 to 50:1 was nearly 9 percent. On a modern 250, that can be as much as 4 horsepower. The loss from 18:1 to 100:1 was nearly 18 percent. The reason for the difference in output is simple. More oil provides a better seal between the ring and the cylinder wall. "
 
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jaguar

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#7
Husqvarna did some testing in the mid 70's that was very interesting. They put 3 identical stock engines on a dyno and ran them for several days at varying RPM and load conditions. Then the motors were torn down and inspected. The engine running CASTOR based oil had the least wear, followed by the synthetic oil, and finally the engine running standard 2-cycle oil.
A second test they performed was to run synthetic in 2 identical engines, one was run at 24:1 and the other was run at 50:1 The engine that ran 24:1 had less piston skirt wear, and less rod bearing wear, but had the same main roller bearing wear as the engine run at 50:1.

Maxima CASTOR 927 has an unpublished % of castor oil and under 50% Group 5 ester oil. I also read that castor oil smokes 50% less than regular petroleum engine oil. The main reason I've been using synthetic oil is that it smokes very little but I may just try Castor 927 since I regularly tear down the engine any way (so I can check for excess deposits in the ring lands).