All About 2 Stroke Engine Oils

This page has all the best info I could find about engine oils and considerations when choosing the fuel/oil ratio. This is a long read so I want to tell you my conclusions first and then you can read why.

OIL TYPES- First we need to change how we talk about types of engine oils. Realize that the descriptive term "synthetic oil" has basically lost its meaning thanks to a court case that allowed oil manufacturers to label highly refined petroleum oil (group 3) as synthetic because it is nearly as good as true synthetics.
There are 5 groups of oils: 1. refined petroleum oil, 2. moderately refined petroleum oil, 3. highly refined petroleum oil, 4. PAO synthetic oil, 5. ester synthetic oil.
So an oil that is labeled as "synthetic" can be highly refined petroleum oil or true synthetic oil. So it's now a very non-specific term. I prefer to understand the qualities of each type of oil and then read the oil specifications to know exactly what is in it. On this page you can see what is in each oil. Oils not listed here are ones that don't publish the oil specifications or are ones not very popular or not very good.

OIL TYPE RECOMMENDATIONS- I recommend a group 3 oil or a mix of petroleum oil (group 1/2) with true synthetic oil for air cooled engines with iron sleeved cylinders because they need higher amounts of oil for best ring protection and power. For high RPM racing engines I recommend any oil with high amounts of castor oil such as Maxima Castor 927. For water cooled engines with power valves I recommend group 4 or 5 oils for the lack of residues they leave on the valves, or a semi-synthetic with a high percentage of group 4 or 5 oil.

OIL RATING RECOMMENDATIONS- I've always known that a fouled plug is one with too much combustion residue accumulated on it to the point that it won't consistently spark. And I knew that if the fuel/air ratio was too rich that a fouled plug was eventually the result. But I didn't know, before extensively studying the topic of motorcycle engine oils, that engine oil can contribute to that problem if it doesn't match the engine. For high heat engines using NGK # 9 or 10 spark plugs I recommend an oil with a TC/FB/FC rating. For lower heat #6 to 7 plug engines I'd recommend an ashless oil or one with an FD rating.

Street vs Race Engines and Viscosity Index
A race engine revs to higher RPM and usually just uses the upper RPM within the pipes powerband whereas a street or enduro bike uses a wide range of RPM. So if the engine oil in a street/enduro bike is at the right ratio for its top RPM but has a low viscosity index (below 120) then there will be too much viscosity at lower RPM and it will produce viscous friction. So for bikes that use a wide range of RPM I recommend oils that have a viscosity index equal or higher than 120.

The Ash Additive
Oils are either "low ash" or "no ash". The word ash is referring to the remaining residue from an oil additive that is one or more minerals (Calcium or Magnesium Phenate) that serve as dry lubricants (for the rings/cylinder and power valves) that can leave an ashey residue when the engine temperature is not high enough to burn it off. So oils are rated as either "ashless" or are rated "low ash" which is either having less than .18% ash (FD rated), or as having .18% to .25% ash (TC/FB/FC rated). Most oils are TC/FB/FC rated which are made for "high heat" engines. What constitutes "high heat"? Air cooled engines, or high RPM engines (over 10K), or most small engines fit that category. But there is no definitive guideline other than looking at their spark plugs heat range which needs to match the engine heat to have their center electrode get hot enough to burn off combustion residue but not so hot as to cause pre-ignition. So for # 9 or 10 NGK spark plugs I would make sure the oil is a low ash oil for the extra protection it gives during high heat engine temperatures. This information is good to know for reducing engine wear and for reducing occurences of plug fouling. So if you want to foul plugs less often or make your rings last longer then I suggest you make sure you are using an oil that is correctly rated for your engine.

Fuel/Oil Ratio
Some oil manufacturers have known all along how to choose a ratio depending on oil characteristics and type engine use. But they have never shared that with us, probably to be free of liability. So I have come up with a system using the oil viscosities, max RPM, and type of engine cooling to be able to know a baseline amount of oil to use. But ony about half the available oils have their data revealed on the manufacturers websites. I do not recommend anyone buying oils without data because really you don't know what you're buying. They can call it 100% synthetic when in reality it is 30% synthetic (for example the Goldfire Pro oil claims to be a synthetic blend but it only has group 1 + 2 oils). There are no "oil cops" to punish them when they scam with lies. Additives do make a difference but not by a huge amount. All I go by is the oils data, not by any hype the manufacturers try to pour into my brain. I am no longer under their thumb of propaganda and if you read this long report you will be free also and can make smart choices for which oil and ratio you use. If the label says use from 20:1 to 50:1 you will no longer think What-The-Fuck? If they list the data on their site (or if you can get it by emailing them) then you can use my Oil Ratio Calculator to know a moderate amount of oil to use.

Things to consider about each oil:
1) Is it "low ash" or "no ash"?
2) Its rating by the rating companys API and/or JASO.
3) Its data: viscosity, viscosity index, and flash point temperature.
4) Its price.
5) Its availability.

The "ash" additives- they are minerals that help reduce friction when there is not enough oil to do the job. But they leave ash residues that only burn off at high RPM high heat so the low ash oils aren't for low RPM water cooled engines such as boat engines. If you use a "no ash" oil in a high RPM high heat engine then make sure you are using extra oil so that the mineral additives are never needed.

Ratings- Most oil manufacturers won't have ther oils officially tested and so they just make an assumption of what rating it is close to. If an oil bottle doesn't have the 9 digit JASO code then it hasn't been rated by JASO. For example Motul 710 has the code 033MOTO64 on it and the letters FD below it. That means they spent the money to have it tested. Most oils are listed as TC or FC which means under .25% ash. FC also means minimal smoke. FD means minimal smoke and under .18% ash which is best matched to engines over 250cc and are water cooled. Click here for the JASO list of registered oils and their rating.

Oil Data-
Viscosity: The ability of the oil film to prevent contact between metals such as the rings and cylinder. Generally speaking the more viscous or thicker an oil, the greater load it will carry.
Viscosity Index: The higher it is the less viscosity will reduce as engine heat increases. So a high viscosity index is best for engines that use a wide range of RPM (vs a race engine that only uses the top 2000 RPM). If you know the 40ºC and 100ºC viscosities then at this site you can calculate its viscosity index.
Density: The higher the density the more the oil weighs. I personally use this to weigh my oil instead of using a measuring cup (which often are inaccurate). I divide the gasoline amount by the fuel/oil ratio and then multiply that by the density to get the needed amount. A metric example would be this: 2 liters (2000 ml) gasoline divided by 35 (from a 35/1 fuel/oil ratio) is 2000/35=57 and then multiply 57 by the oil density .87 to get 50 which means I need to add 50 ml of oil to 2000 ml of gasoline for a 35/1 ratio. An imperial measurement example would be this: 2 gallons (256 oz) gasoline divided by 35 is 7.3 which multiplied by .87 is 6.4, so 6.4 ounces need to be added to 2 gallons gasoline for a 35/1 ratio.
Flash Point Temperature: The temperature at which the engine oil can vaporize and burn. Usually the lower the flash point the more kerosene-like thinner they have in it. The listed flash point temp doesn't reflect the flash temp of the actual base oils which are usually 215C - 300C except for group 1 oil which can be as low as 75C. I generally ignore the flash point because it say nothing about the base oils.
Oil Groups: since group 3 oil is technically a refined petroleum oil but also legally a "synthetic" oil (because it has such good properties) I choose to describe oils by their content of the different groups of oil instead of saying mineral/semi-synthetic/full-synthetic*. Group 1-3 are refined petroleum oils. Group 4 is synthetic PAO oil. Group 5 is synthetic and usually ester. The higher the number, the higher the quality. This info is from the oil manufacturers** which sometimes makes it obvious they are lying about its content (labeling it as full synthetic when it's not) or at what ratio you can use it at.
* the exception to this is when the full data is not available for me to list the oil group.
** they only give the CAS #'s of the ingredients but those can be looked up on the internet.
Ratings: When "unapproved" the rating is one assumed by the oil maker. Most unrated oils meet the TC requirements and are low ash oils that produce significant smoke. When they are unapproved I sometimes include a different rating that I think is more appropriate according to the oils specs.

I offer an Excel spreadsheet for detemining the right gas/oil ratio. Click here to read about it.

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PJ1 Goldfire Pro (data: #1  #2)
Cost: $20.66/liter
over 35% group 2 oil (CAS 64741-88-4), under 30% group 1 oil (CAS 64742-47-8)
Viscosity 7.1 @ 100C, 42 @ 40C, viscosity Index 128, .87 density, 95ºC flash point
rating: unrated (probably equal to TC due to its group 1 + 2 oils)
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Spectro Oils 2T (data #1  #2)
Cost: $9.95/liter
60-90% group 1 and group 2 oils (CAS 64742-01-4 + 64741-88-4)
Viscosity: 9.4 @ 100ºC, 77.1 cST @ 40ºC, viscosity index 97.6, .88 density (estimated),
Flash point: 165ºC
ratings: API-TC
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Bel-Ray Mineral 2-Stroke Oil (data #1  #2)
Cost: $6.99/liter
90% group 1 + 2 oils (CAS 64741-88-4 + 64742-52-5 + 64742-01-4)
can be used with E15 gas.
viscosity 8.5 @ 100ºC, 59 @ 40ºC, viscosity index 116, density .88, flash point 73ºC (175C for base oils)
rating: API TC and JASO FB
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Yamaha Yamalube 2R (data: #1  #2)
Cost: $12.09/liter
Under 69% group 2 oil (CAS 64742-54-7), 17% group 1 oil (CAS 64742-47-8)
For the high temperatures, rigorous demands and stresses of competition engines.
8.5 viscosity @100ºC, 55 @ 40ºC, Viscosity Index 128, .88 density, 174ºC flash point
rating: not tested (probably FC due to its group 1 + 2 oils)
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Amalie SynPlus Oil 20W-20 (data #1  #2)
Cost: $5.09/liter (32oz)
82% Group 2 oil (CAS 64742-54-7)
For high performance air-cooled 2-cycle motorcycles and smaller four-cycle engines.
7 viscosity @100ºC, 42 viscosity @ 40ºC, Viscosity Index 126, .87 density, 190ºC flash point, .08% ash
unapproved rating: JASO FD
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Bel-Ray SL-2 (data: #1  #2)
Cost: $7.48/liter
30% synthetic, 30-40% group 1 oil (CAS 64742-47-8)
8.1 viscosity @ 100ºC, 41 @ 40ºC, viscosity index 176, .86 density, 86ºC flash point
unapproved rating: JASO FD (note: FD is low smoke but group 1 oils are smokey so I would assume its rating is FC)
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Motul 510 2T(data: #1  #2)
Cost: $11.99/liter
synthetic oil (assumed due to the viscosity index although it isn't listed in the data sheet),
25-50% group 2 (CAS 64742-54-7), 10-25% Group 1 oil (CAS 64742-46-7)
viscosity 8.2 @ 100ºC , 66.5 @ 40ºC, viscosity index 89, .86 density, 117ºC flash point
ratings: JASO FD
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Motul Scooter Expert 2T (data: #1  #2)
Cost: $18.37/liter
synthetic oil (assumed due to the viscosity index although it isn't listed in the data sheet),
25-50% group 2 (CAS 64742-54-7), 10-25% Group 1 oil (CAS 64742-46-7)
Engine oil with high RPM protection, OK for ethanol and catalytic converters.
viscosity 9.1 @ 100ºC, 56.2 @ 40ºC, viscosity index 142, .86 density, 92ºC flash
approved ratings: JASO FD
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Putoline MX5 (data: #1   #2)
Cost: $13.46/liter
synthetic oil (unspecified), 25-50% group 1 oil (CAS 64742-47-8)
viscosity 6.75 @ 100C, 33.7 @ 40C, viscosity index 153, flash point 122C, density .85
unapproved rating: API TC
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Bel-Ray MC-1 Racing (data #1  #2)
Cost: $26.44/liter
group 5 synthetic Ester oil, 20% Group 2 oil (CAS 64742-52-5)
For non-power valve air engines. Good in vintage engines.
viscosity 20.3 cSt @ 100ºC, 244 @ 40ºC, viscosity index 97, density .93, 98ºC flash point
ratings: unrated (since it is good in air cooled engines I would assume a TC rating for its ash content)
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Lucas High Performance Semi-Synthetic 2-Cycle Oil (data: #1  #2)
Cost: $11.34/liter
synthetic oil (assumed by the viscosity index although it isn't listed on the data sheet),
10-30% group 1 oil (CAS 64742-88-7)
viscosity 7.5 @ 100ºC, 41.5 @ 40ºC, viscosity index 149, .87 density, 83ºC flash point, .25% ash
unapproved rating: JASO FC
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AMSoil Dominator (data: #1  #2)
Cost: $13.63/liter
25-40% group 5 oil, 30-50% group 1 oils (CAS 64742-47-8 + 64742-48-9)
viscosity 7.2 @ 100ºC, 36.5 @ 40ºC, viscosity index 165, .87 density, 102ºC flash point
unapproved rating: API TC
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Shell Advance Ultra 2T (data)
Cost: $22.83/liter
Group 3 oil
viscosity 9 @ 100C, 68.9 @ 40C, visc index 104, flash point 102C, .88 density, .11% ash
unapproved rating: JASO FD
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Maxima Scooter Pro Oil (data: #1  #2)
Cost: $9.95/liter
20% synthetic (group 4 or 5), 65% group 1 + 2 oil mix (CAS 64742-48-9 + 64742-54-7)
viscosity 8.9 @ 100ºC, 44.56 @ 40ºC, viscosity index 185, density .86, 190ºC flash point
unapproved rating: API TC

Motul 710 2T (data: #1   #2)
Cost: $18.99/liter
Synthetic oil (asumed due to the viscosity index), 10-25% Group 1 oil (CAS 64742-46-7)
viscosity 8.9 mm2/s 100C, 46.4 mm2/s 40C, viscosity index 176, .86 density, 88ºC flash point
approved rating: JASO FD
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Putoline MX9 (data: #1  #2)
Cost: $25.91/liter
Synthetic group 4 or 5 (unspecified), 25-50% Group 1 oil (CAS 64742-47-8)
Viscosity 8.8 @ 100C, 44 @ 40C, VI 185, flash point 78C, density .88, .26% ash
unapproved rating: JASO FD (note: with .26% ash it should be rated TC)
Note: Putoline shows MX7 to have all the same specifications and it's a little cheaper.)
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Motorex Power Synt 2T (data: #1  #2)
Cost: $26.10/liter
synthetic group 4 or 5 (unspecified), 25-50% group 1 oil (CAS 64742-47-8)
viscosity 9.1 @ 100C, 50.1 @ 40C, viscosity index 164, flash point 98C, density .87
approved rating: JASO FD
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Motorex Cross Power 2T (data: #1)
Cost: $19.35/liter
Synthetic group 4 or 5 (unspecified), 10-30% Group 1 oil (CAS 64742-47-8)
viscosity 9.6 @ 100C, 56 @ 40C, viscosity index 156, .87 density, flash point 110C
unapproved rating: JASO FD
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Bel-Ray H1-R (data #1  #2)
Cost: $19.99/liter
group 5 synthetic Ester 2 stroke oil
For use in engines with or w/o power valve, and for racing karts.
viscosity 12.4 @ 100ºC, 141 @ 40ºC, viscosity index 72, .95 density, 202ºC flash point
unapproved rating: JASO FD
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Maxima Super M (data: #1  #2)
Cost: $12.99/liter
<60% Group 5 oil (CAS 11138-60-6), 25% synthetic
Smokeless, low ash, for use in all high performance 2-stroke engines.
12.3 viscosity @ 100ºC, 96.5 @ 40ºC, viscosity index 120, density .86, 138ºC flash point
unapproved rating: Exceeds JASO FC (since it's synthetic clean burning makes it like FD. It probably has an ash level for FC though.)
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Maxima FORMULA K-2 High RPM Formula (data: #1  #2)
Cost: $17.95/liter
70% Synthetic oil, 7.5% group 1 oil (CAS 64742-88-7)
2000 centistoke esters along with special additives.
13.6 viscosity @ 100ºC, 97 @ 40ºC, viscosity index 141, density .86, 116ºC flash point
rating: unrated (since it's made for high RPM I assume it's FC due to ash cotent nad being mostly synthetic)
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Honda Pro Honda HP2 (data: #1  #2)
Cost: $17.60/liter
70-90% synthetic group 4 or 5
viscosity 17.8 @ 100C, 167 @ 40C, viscosity index 117, flash point 105C, density .94
rating: unrated (since it is made for their MX bikes I would assume FC)
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Silkolene Comp 2 Plus (data: #1  #2)
Cost: $14.95/liter
made with group 5 oil (ester)
viscosity 12.54 @ 100C, 83 @ 40C, 149 viscosity index, flash point 84C, .88 density
unapproved rating: JASO FD
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Red Line AllSport (data: #1  #2)
Cost: $18.72/liter
under 45% group 5 oil (CAS 68334-05-4), under 25% group 1 oil (CAS 64742-47-8)
For stock to moderately modified engines.
15.4 viscosity @ 100ºC, 89.6 @40ºC, viscosity index 183, density .88, 155ºC flash point
unapproved rating: JASO FC
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ELF HTX 976+ (data: #1  #2)
Cost: $23.37/liter
Group 4/5 oil
viscosity 17.7 @ 100C, 148 @ 40C, visc index 132, flash point 208C, .92 density, less than .15% ash
rating: unrated (because it's synthetic and has a low ash content I would assume FD)
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Motul 800 2T Off Road (data: #1   #2)
Cost: $20.20/liter
Group 5 oil, 6% Group 2 oil (CAS 64741-88-4)
For racing premix 2 stroke engines operating at high revs and under high load.
15.5 mm2/s viscosity @ 100ºC, 120 mm2/s viscosity @40ºC, viscosity index 135, .91 density, 252ºC flash point
unapproved rating: API TC (since it is mostly synthetic and its made for high stress engines I would assume its rating is close to FC)
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Motul Kart Grand Prix 2T (data: #1  #2)
Cost: $18.50/liter
Group 5 oil
Especially designed for karting and RC engines running at extreme revs up to 23,000 RPM.
viscosity 16.9 @ 100C, 135 @ 40C, viscosity index 136, .92 density, 256C flash point
unapproved rating: API TC (since it is mostly synthetic and its made for high stress engines I would assume its rating is close to FC)
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MOTUL 800 2T Road Racing (data: #1  #2)
Cost: $16.79/liter
Group 5 oil, 6% Group 2 oil (CAS 64741-88-4)
For racing premix 2 stroke engines operating at high revs and under high load.
viscosity 19.2 @ 100ºC, 157.4 @ 40ºC, viscosity index 140, .93 density, 274ºC flash point
unapproved rating: API TC (since it is mostly synthetic and its made for high stress engines I would assume its rating is close to FC)
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Repsol Moto Off Road 2T (data: #1  #2)
Cost: $29.95/liter
Synthetic oil for high performance 2-stroke engines
viscosity 10 @ 100C, 64 @ 40C, viscosity index 141, density .87, 130C flash point, .1% ash
approved rating: JASO FD
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Repsol Moto Racing 2T (data: #1  #2)
Cost: $37.95/liter
Synthetic oil for high performce high RPM engines, including karts.
viscosity 18 @ 100C, 150 @ 40C, viscosity index 133, density .92, 200C flash point
unpproved rating: JASO FD
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Klotz BeNOL Racing Castor (data: #1  #2)
Cost: $14.74/liter
Castor oil
viscosity 15.7 @ 100C, 166 @ 40C, viscosity index 96, .93 density (estimated), 291C flash point
ratings: unrated (since it is castor oil and it's made for high stress engines I would assume its rating is close to TC)
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(best for engines reving under 10,000 RPM)

Maxima CASTOR 927 (data: #1  #2)
Cost: $21.05/liter
under 50% Group 5 ester, castor oil, 10-20% additives to reduce carbon and gum formation.
15.2 viscosity @100ºC, 155 viscosity @ 40ºC, viscosity index 98, density .92, 218ºC flash point
rating: unrated (I would guess a TC rating)
Note: although this oil is ashless it is OK for high reving engines because of its castor oil content.
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Maxima Premium 2 (data: #1  #2)
Cost: $13.49/liter
20-40% synthetic group 5, 20-40% group 1 + 2 oil mix (CAS 64742-48-9 + 64742-54-7)
viscosity 8.8 @ 100ºC, 51.7 @ 40ºC, viscosity index 126, density .87, flash point 126ºC
unapproved rating: TC-W3 (because it is ashless and has a fair amount of group 1 oil)
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Royal Purple HP 2-C synthetic oil (data: #1  #2)
Cost: $12.00/liter
synthetic oil (assumed due to the viscosity index although its not listed in the data sheet), 20-50% group 1 + 2 oils (CAS 64742-47-8 + 64741-89-5)
viscosity 7.5 @ 100ºC, 46 @ 40ºC, Viscosity Index 129, 116ºC flash point
ratings: unknown (I would guess it is close to TC)
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OILS I WON'T LIST IN MY RATIO CALCULATOR due to an artificial viscosity

Red Line Two Stroke Racing Oil (data: #1  #2)
Cost: $24.67/liter
under 25% group 5 oil (CAS 68334-05-4) and <25% group 1 oil (CAS 64742-47-8)
Viscosity 42.3 mm2/s @ 100ºC, 191 mm2/s @ 40ºC, viscosity index 272, density .91, 147ºC flash point
Note: this oils viscosity exceeds any of the best oils by at least two times as much, and with under 25% of synthetic oil and under 25% of the cheapest oil (group 1) I think the 6% added polymer in their product artificially doubled the viscosity. It is known that Polyisobutene (PIB) increases viscosity greatly but doesn't increase the protection because it isn't a lubricant. So this is just listed here as an example of the advantage of researching a product. With these doubled viscosities it is useless to input them into my oil ratio calculator to see what ratio it should be used at.
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Golden Spectro Motorcycle Pre-mix (data: #1  #2)
Cost: $22.18/liter (33.8 oz)
70-90% Group 1 + 2 oils (CAS 64742-47-8 + 64742-01-4 + 64742-52-5)
12.8 viscosity @ 100ºC, 102 viscosity @ 40ºC, viscosity index 121, 77ºC flash point (157C for its base oils)
unapproved rating: API TC
Note: this oils listed viscosities are too high for group 1 + 2 oils. It's probably as good as Yamalube but I can't rely on its viscosities to run it in my calculator.
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Interlube Opti-2 Two Cycle Oil (data)
Cost: $27.37/liter
synthetic oil (assumed due to viscosity index), over 50% group 2 (CAS 64742-54-7), under 13% group 1 (CAS 64742-88-7)
viscosity 13.4 @ 100C, 101 @ 40C, viscosity index 131, .86 density, flash point 154C
Note: the listed viscosities are too high for what is to be expected with mostly group 1/2 oils so I think as part of their extensive additive package they included polymers to artificially boost the viscosity without boosting the protection since polymers aren't lubricants.
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Klotz Super TechniPlate (#1  #2)
Cost: $12.75/qt
Contains 80% Original TechniPlate synthetic lubricant and 20% BeNOL Racing Castor
viscosity 22.4 @ 100C, 152 @ 40C, viscosity index 169, .995 density, flash point 208C
rating: TC equivalent
Note: this products viscosity is abnormally high for a synthetic/castor blend. Instead of 22.4 @ 100C it should be between 15 and 20. So I think this has polymers in it to artificially boost the viscosity.
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Klotz Motorcycle TechniPlate TC-W3 Lubricant KL-302 (data)
Cost: $12.77/liter
(They claim it's synthetic but the viscosity #s reflect group 1-3 oils)
40C/100C/150C/200C viscosities 48.9/7.1/2.95/1.66, viscosity index 102, flash point 135C
unapproved ratings: JASO FD, ISO-EGD, NNMA TC-W3 (if it has group 1-3 oils then it would produce too much smoke to pass the FD + EGD test)
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Castrol Go! 2T (data: #1  #2)
Cost: $8.07/liter
over 90% "highly refined" oil which normally means group 2
11 viscosity @ 100ºC, 94 viscosity @ 40ºC, Viscosity Index 102, 194ºC flash point, density .88
ratings: API TC and JASO FB
Note: this products viscosity is too high for group 2 so probably polymers are added to artificially boost the viscosity.
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Concerning the oil groups above:
In the petroleum industry there's a huge grey zone in determining what group and CAS # a batch of base oil can be classified as. That is because there is huge variation in the composition of oils from different locations and from different depths. And the final processed oil depends on the original unprocessed oils composition. As a result each CAS # is very vague and lists a range of carbon #'s (ie: C20-C50) instead of listing one. And the other aspects are all listed as a range also. So when a company publishes an oils viscosity and flash point it is just the running average among many different batches and each bottle may vary significantly from previous bottles. This is anything other than an exact science. So my determination of which group an oil belongs in came from looking at the data and not what was claimed by the company. I found the CAS #'s for most of the oils but when I looked them up they never listed a group # to associate it with. I had to guess at it according to all the variables, especially the base oils flash point.
But the bottom line for any engine oil is not the supposed group # but the viscosity at 150C and 200C. Those mostly determine the fuel/oil ratio. How much extra oil you can add is limited by smoke, carbon deposits, spooge, and plug life.

Factors affecting the need for either a low ash or ashless oil:
1) water or air cooled.
Water cooled engines can operate with higher compression ratios than air cooled engines since the increased cooling counters the tendency to increased cylinder/head heating from the high compression.
2) engine compression ratio
The combustion temperature in a high compression engine (over 150psi) is higher than in a lower compression engine, regardless if it is water cooled or not.
3) max RPM and how much time is spent at/near max RPM.
Reving at high RPM produces higher cylinder/ring temperatures which requires better lubrication.
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Here's some quotes emphasizing how viscosity is of primary importance:

Viscosity is the single most important physical property of a lubricant. It is a crude measure of a lubricant's molecular constitution from the standpoint of hydrocarbon chain size. Viscosity determines film thickness and film strength.

Viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress.

Viscosity is very important because it affects the oil's ability to reduce friction and transfer heat.

An oils first line of defense is its viscosity (thickness). The ability of the oil film to prevent contact between the rings and the cylinder is a function of an oils viscosity. Generally speaking, the more viscous or thicker an oil, the greater load it will carry.

To double check I spoke on the phone with Joey Cabrera at Motul and he assured me that I was on the right path by thinking that the principle consideration is the final mixed viscosity. He also assured me that viscosity index and flash point are indicators of the quality of the product. (A low flash point temperature usully indicates a fair amount of group 1 oil or added solvent.)

The Different "Types" of Oil

There are basically two different types of oil available. We have straight mineral based oils, straight synthetic oils, and something called a semi-synthetic which is a blend of the two.

Mineral based oils are generally known for good lubrication properties while the engine is running and then, while the engine is sitting between flights, the mineral oils do a great job of keeping the internal parts of the engine coated with a fine film that keeps rust from forming. However, there have been complaints about excessive carbon deposits and excessive smoke when straight mineral-based oils are used.

Synthetic oils are generally known for having excellent lubrication properties with low deposits and they can be used at higher fuel/oil ratios (for less oil) because their viscosity and viscosity index, and flash point temperature, is higher. Let's define "synthetic." Where traditional mineral (or conventional) oils use refined petroleum, synthetic oils consist of chemical compounds that are artificially made by breaking down and then rebuilding petroleum molecules. The end result is an oil containing specific molecules that are tailored to provide optimal lubrication properties. These are the group 4 and 5 oils. Legally group 3 mineral oil is considered synthetic because its properties are basically equal to synthetics.

100% synthetic oil uses a synthetic base stock mixed with a variety of additives that boost the performance of the oil. While all synthetics on the market may offer a higher level of protection than conventional or synthetic blends, not all synthetics are equal. Each synthetic brand uses a mix of high-performance fluids and additives. How these formulations come together results in various protection levels and attributes.

The main difference between mineral and synthetic oils are the synthetics ability to maintain good viscosity when temperature rises to an extreme (evident by the higher viscosity index numbers).

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2-cycle oil comes in two basic types: Air-cooled and water-cooled/outboard. The "air-cooled" type is designed for higher operating temperatures and RPM and contains a "low-ash" detergent. The "water-cooled/outboard" type is designed for lower operating temperatures and RPM, and contains an "ashless" detergent. Either type is not recommended for the other's application, due to various concerns. The type for water cooled low RPM engines leaves no ash since if it did then the lower engine temperatures wouldn't burn it off which would let it stick and build up on surfaces and foul plugs.
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Which type oil for 2 strokes?
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 group 3 oil. It is so good that legally it is allowed to be labeled as a synthetic oil. But there is only one for sale in the USA and that is two oils made by Legend Performance.
Legend is made of the rare and elusive group 3 type oil that is
1) very combustible mineral oil which boosts power,
2) highly refined mineral oil so that its protective properties are like synthetic oils. Legally they can call it synthetic because of that.
So you get the extra power from a mineral oil and top protection at high RPM like with a synthetic oil.

Legend emailed me in response to my request for all the technical data on their oils and they replied: "Snowmobile oils require low pour points (-30- to -50 below zero F) for oil injection applications so that they can flow freely enough to pump. Motorcycles rarely operate in those frigid conditions. 2T oils are classified as Pre-Mix, Injection or both such as our products.
Our oils can be used in any two-cycle application as long as they meet current API / JASO specification called out by the manufacturer. This is important when warranty coverage is in effect. Our ZX-2SR has the highest JASO FD Rating and therefore is warranty Compliant.
Short answer is use our ZX-2R (JASO FC) for any pre-2010 application up to 10,000 rpm, or use our ZX-2SR Race Oil for any engines 2010 and nearer, still under warranty or with high rpm in excess of 10,000. We have a lot of motorcycle riders who use our product in recreational and racing venues.

We do not publish Flash Points or other proprietary info of our oils."

At $165 for 4 gallons at first you may think it is expensive but that is only $11.34/liter which is $1.65 less than Super M synthetic by Maxima.
Here is their website from which you can order it:

Shell Advance Ultra 2T also is made with group 3 oil but is not available in USA.

So the next best oil would be a good semi-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.

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from an article written by Robert Verret:

The two types of detergents/dispersants most commonly used in 2-stoke oil formations are Ashless and Low Ash. Medium Ash and High Ash detergents are not used in 2-stroke oils. Ashless detergents are used in low temperature applications such as TCW3 oils where the ring land temperature is held below 300 deg F. These detergents work well in engines where an excess of cooling capacity is available and power valves are not used. Ashless detergents are manufactured from organic nitrogen compounds (Hydrazine) instead of heavy metal compounds; therefore, they produce no ash as they are burned away. This is where the name "Ashless" comes from. Oils containing this type detergent have a characteristic ammonia odor. Low Ash type detergent/dispersants are used in most API-TC, Jasco FC and ISO GC certified 2-stroke oils. These oils are designed for air-cooled high performance engines that operate under severe load/temperature conditions. Low Ash detergents can keep the deposits to a minimum at ring land temperatures as high as 400 deg F (204ºC). These detergents are manufactured from compounds of Calcium and Magnesium. After these compounds (Calcium Phenate or Magnesium Phenate) do their job, they burn away, forming a heavy metal salt (ash) that is swept away during the normal combustion process. Hence, this is where the name Ash-type detergent comes from. Ash type detergents depend on the higher combustion temperatures to keep the resulting ash swept out. Therefore, the use of these high performance oils in outboard or other mildly tuned 2-stroke engines is not recommended. Some manufacturers are using a combination of detergent types (Ashless and Low Ash) to provide a broader range of uses for their oil. It is important to note that oil designed to meet TCW3 specs only (Ashless) will not protect an engine requiring API-TC (Low Ash) type oil. The converse is also true. Using a Low Ash oil in an engine designed for an Ashless type oil only could result in fouled plugs and gummy combustion chambers. When 2-stroke oil is kept in its temperature limits, it provides an adequate protective film between all moving parts. When that maximum temperature is exceeded, the oil film breaks down and usually seizure occurs unless another line of defense is added to the oil mixture. These are the Antiwear agents. These Zinc compounds (Zinc Dithiophoshate) flow in with the oil and are never used unless the base oil breaks down. If the base oil breaks down, they form a protective barrier between the moving parts (usually piston skirts and cylinder walls).
The API TC standard was developed for air-cooled, high RPM, high output 2-stroke engines operating under severe load conditions. Although this standard is no longer reviewed and updated since 1993 by the API, it still is in effect today. This standard most accurately addresses the condition Rotax and 2-stroke racing motorcycles and snowmobiles operate under. Almost all these oils are formulated with synthetic or synthetic blend base oils and all use a low ash type detergent.
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Primary materials in 2-cycle oil formulations:
1) Base Oil- Mineral oil or synthetic oil but not including polybutenes.
2) Additives- To improve lubricity and detergency. detergents, dispersants, anti-wear agents, EP agents.
3) Polybutenes- To improve reduction of exhaust smoke.
4) Distillates - to improve handling and fuel miscibility distillates are added such as kerosene, gas oils, or other solvents.

The temperature stability (viscosity index) of an oil can be improved with a viscosity modifier but they are significantly more expensive than most base oils and most synthetics.
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Since the oil needs to match engine heat we may be able to tell which type oil is best to use by the # of NGK spark plug is best in our engine since that too has to match engine heat. #'s 8 and 9 are used on 250cc and 500cc, and #'s 9 and 10 are used on 125cc and 80cc. (The larger the engine the lower the RPM and the lower the engine heat.) So for # 9 or 10 NGK spark plugs I would make sure my oil is a low ash oil for the extra protection it gives during high heat engine temperatures.
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If you are like me you want the best value as well as the best protection. So if we divide their manufacturer suggested cost per liter by the fuel/oil ratio recommended by my spreadsheet then we get the comparative costs listed below. The lower the number the greater the value.

These are for air cooled engines reving to 10,000 RPM
$.20 Amalie SynPlus
$.27 Bel-Ray SL-2
$.37 Maxima Scooter Pro
$.40 Yamalube 2R
$.44 Motul Scooter Expert
$.48 Lucas semi-synthetic
$.50 Spectro 2T
$.50 Maxima Premium 2
$.52 Royal Purple HP 2-C
$.54 Motul 510
$.57 Amsoil Dominator
$.77 Putoline MX5
$.88 Shell Advance Ultra
$.93 PJ1 Goldfire Pro
These are for water cooled engines reving to 10,000 RPM
$.24 Klotz BeNOL
$.25 Motul 800 Road Racing
$.28 Maxima Super M
$.30 Red Line AllSport
$.30 Motul Kart Grand Prix
$.31 Motul 800 Off Road
$.35 Honda HP2
$.35 Maxima Formula K-2
$.41 Maxima Castor 927
$.42 Motul 710
$.44 Bel-Ray H1-R
$.48 Motorex Cross Power
$.48 ELF HTX 976+
$.60 Repsol Moto Racing
$.72 Putoline MX9
$.72 Motorex Power Synt
$.73 Repsol Moto Off Road

The flash point temperature is better the higher it is because that indicates absence of group 1 mineral oil or absence of solvents. Also a lower flash point oil will lower the gasolines octane so the higher the flash point, the better. So if your engine is high compression and you are using high octane gas then you should try using an oil with a higher flash point (full or part synthetic) in order to avoid any possiblity of detonation. In the old days, when all of the two strokes were developed, they all used Castrol petroleum oil at a 20:1 ratio and found that 92 octane gas had the octane reduced to 72 with presence of that much oil.

A research paper used a 167cc 4 stroke engine with 6.6 compression ratio to record 250ºC at the piston edge @ 5000 RPM which could be projected to be 300ºC at 9000 RPM. The rings will be a cooler since they are farther from the hot piston center and they are the thermal conduit between the piston and the cooler cylinder. And the cylinder is gradually cooler with distance down from its top. So if we guess at the average ring temperature as being 200ºC on air cooled engines then we need to calculate for an engine oil viscosity at that temp for comparison of oils for use in air cooled engines. So for the oils that have their 40ºC and 100ºC viscosities listed then the 150ºC and 200ºC viscosities are calculated from an online calculator.

Cylinders which are chromed are slicker and need less oil but the piston rings are softer and need the same amount of oil as an iron sleeved cylinder (with hard rings). All cylinder liners (sleeves) are about a class 40 grey cast iron composition. The hardness can vary greatly depending on the kind of heat treating which was used. Steel is never used in cylinder liner composition.

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Recommendations from Maxima Oil Company (

I commend Maxima for making this info available. Most manufacturers don't make any info available to help people better pinpoint the fuel/oil ratio they need. But still you can see that the range they list is still leaving you to guess at the best ratio for your engine. Also it looks like these ratios apply to mineral oils since their extreme use ratios are around 20:1. Synthetic oils have extreme ratios above 35:1 so this list is not for the more popular synthetic oils.
Engine sizeinfrequently
wide open throttle
cross country
mostly WOT use
road racing, track racing
250cc +50-60:140:125-32:1

I asked Tim Schaeffer the representative of Maxima Oils: "how would you rate these oils for a small displacement air cooled street bike that sometimes has long high RPM runs on the highway?"

He replied: "Given the operating conditions I would rate these oils in this order: Castor 927, Formula K2, Super M, Premium 2, Scooter Pro."

So he favors formulas with castor above everything else and then goes by the % of synthetic oil in each. The more synthetic, the better the high RPM protection.

Contrast the above recommended ratios to the most common lie by some lazy and stupid oil manufacturers so plainly expressed in this online quote by AMSoil: "Because one mix ratio satisfies multiple pieces of equipment, Saber Professional eliminates mix ratio confusion." Bullshit! There's at least 6 different factors affecting what the fuel/oil ratio should be. Ratio confusion exists because they have never fully investigated this subject. Due to their irresponsibility I'll bet that 70% of the bikes in use are using too much or too little oil.

Less Oil NeededMore Oil Needed
low RPMhigh RPM
water cooledair cooled
high viscositylow viscosity
little WOT timemuch WOT time
gas w/o ethanolgas with ethanol
low ambient temphigh ambient temp

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Ethanol containing gasoline ideally should never be used in a 2 stroke engine since the alcohol dries out the crank seals and causes them to have their lifespan drastically reduced. Also the alcohol doesn't immediately vaporize when it contacts the cylinder wall and so it dilutes the oil there, making it less effective at protecting the rings. To find sources of ethanol free fuel, go to this site -> If you have to use it then use only 10% alcohol gasoline, designated E10. Don't use any higher alcohol content gas. And increase the amount of oil added to the gasoline (in premix) or switch to an oil with a higher viscosity. You can get all alcohol out by vigorously mixing in 25% water. The alcohol bonds to the water molecules and settles to the bottom. Then just pour out the gasoline into a clean container and leave the water/alcohol in. Click here to see how.
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Important: Ester synthetics are less burnable than mineral oil or group 3 highly refined petroleum oil. Switching from a mineral oil or semi-synthetic to an ester synthetic may require increasing main jet size. [read more]
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API TC is a certification for two-stroke oils, awarded by the American Petroleum Institute. It is given after the product passes through stringent tests that determine the level of detergent performance, dispersion, and anti-oxidation. It is the only remaining, not revoked classification of the API Two-Cycle motor oil specifications (TA, TB, TC, TD). Being a very old standard itself, most currently produced 2T lubricants meet its specifications, even the lowest quality ones; current high-quality oils exceed them.

API Two-Cycle Motor Oil Specifications

Designed for various high-performance engines (typically 50cc to 500cc) such as those on motorcycles and snowmobiles, and chain saws with high fuel-oil ratios but not outboards. This performance rating is determined by engine tests that evaluate (1) anti-scuff characteristics, (2) piston ring sticking and engine cleanliness, and (3) pre-ignition. Oils with this spec are typically using metal-based, ash-producing additives (under .25%).

JASO Oil 2 stroke Specifications (Click here for their list of registered oils and their rating)

Original spec established regulating lubricity, detergency, initial torque, exhaust smoke and exhaust system blocking.
Increased lubricity, detergency, exhaust smoke and exhaust system blocking requirements over FA.
Lubricity and initial torque requirements same as FB, however far higher detergency, exhaust smoke and exhaust system blocking requirements over FB. (similar to API TC)
Same as FC with far higher detergency requirement.

ISO Two-Cycle Oil Specifications

During the mid-90s it became clear that the JASO Specifications cannot satisfy the requirements of the modern European two-stroke engines. The ISO standards listed below were developed to address this shortcoming. Their basis is the relevant JASO standard + they require an additional 3hr Honda test to be run to quantify piston cleanliness and detergent effect.

Same requirements as JASO FB + test for piston cleanliness.
Same requirements as JASO FC + test for piston cleanliness.
Same requirements as JASO FD + test for piston cleanliness + detergent effect.
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Engine Break In- Most advice I've heard up till now said not to use synthetic oil when breaking in an engine. But since I've found out that synthetics aren't really "slicker" and have about the same wear protection given the same viscosity as a mineral oil. So my advice is to use your normal oil but at a higher fuel/oil raio than normal for at least 15 minutes. Be sure not to run it to extremes so that it won't seize. The idea is to let the rings wear down a bit to perfectly fit the roundness of the bore. That will promote more compression and power later on when you return to using more oil in the gas.

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BelRay info:
The film strength is one of the more important properties of a 2-stroke oil. It needs to withstand the heat and combustion of the fuel without burning and also needs to be able to clean the parts that may have carbon deposits or gummy residues left over from poor combustion or less effective lubricants. Since the thin film of lubricant is the only thing to stop the piston rings from grinding into the cylinder walls, these lubricants must be capable of protecting against high levels of pressure during the stroke of the piston.

Certain 2-stroke lubricants are diluted with solvents to make them "clean burning" and provide "deposit control." This is usually done to compensate for the lack of performance in the base fluid used. Since solvents tend to be highly flammable, the presence of them in the oil will also alter the combustion within the chamber. These solvents will alter the octane of the fuel and act as an impurity, causing detonation. Engines are designed to combust fuel, not the fuel and the extra flammables you'll find in low quality lubricant products. The added combustion of part of the lubricant can result in a poor running engine or even engine failure.

A 100% synthetic ester base engine oil gives a high level of detergency to ensure the elimination of carbon deposits and deter the formation of new performance-robbing deposits. These esters naturally adhere to metal surfaces and create a very tenacious film, so when the lubricant is brought onto the piston, it creates a film and spreads along the surface to protect the entire component. This film is difficult to eliminate, therefore, the engine will remain lubricated through very harsh conditions.
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from Thumpertalk:
The fundamental goal of lubrication is actually to completely prevent the two surfaces having any direct contact whatsoever. There two basic states, or modes, of lubrication. These are "hydrodynamic", wherein the moving parts glide over each other totally separated so that they "plane" on the oil like a skim board, and "boundary", wherein the two parts have forced their way past the oil film and have come into actual physical contact. "Anti-wear" additives are added to the oil to prevent damage during boundary conditions. Next, there is the fact that even the most perfectly machined surface is never perfectly smooth. When looked at under a microscope, "asperities", which are craggy looking high and low spots resembling a mountainous landscape, can be seen. If two such surfaces are moved across one another, the high spots of one dip into the low spots of the other, creating friction. This naturally has a tendency for the two parts to knock the high spots off of each other in the process known as wear.
Anti-wear additives [in "low ash" oils] are usually metallic compounds of zinc, phosphorus, molybdenum, sulfur, etc., whose purpose is to become embedded in the low asperities of the metal surfaces so as to prevent the neighboring high spots from digging into them. This takes place by running the parts together under moderate pressures with a film of oil containing these compounds for a period of time [break-in] long enough to allow it to take place. Once accomplished, the surface is in effect "flatter", which supports the oil film better, improving hydrodynamic lubricity, and the two parts can bear on one another with very high pressures without significant wear taking place. After break-in these boundary lubricants can permanently protect the moving components against damage at times when lubrication is marginal, such as during startup. Ball and rolling element bearings don't break in in this way because their components don't slide over each other as plain surfaces do, but they still depend on hydrodynamic separation, and on the embedding of anti-wear compounds into their contact surfaces. They take considerably less time to receive a viable level of boundary protection, though, and can survive nicely on remarkably little hydrodynamic lubrication after a very short run in period.
Keep in mind the ratios the manufacturers recommend are for a high performance dirt bike that is designed to race at its full capacity. If you have skills like Ryan Dungey and you ride your bike at full noise most of the time you need the recommended petrol to oil mix to keep the piston and rings properly lubricated. On the other hand, if you are just puttering around and spending most of your bikes time in the low to mid revs range, that extra oil is probably an overkill and not entirely needed.

There's a myth that the less oil you use in your gas, the more horsepower you get. Conversely, many dirt riders actually forget to put any oil whatsoever. We know of one guy who forgot to mix oil into his gas and actually rode it for two hours without seizing it. All the bearings were ruined and the piston was worn out, but it didn't seize!
Actually, you can get more horsepower out of a two-stroke engine with extra oil in the gas, because the oil provides a better ring seal and, therefore, more compression. People think that gas burns more efficiently with less oil, and therefore you get more performance. It almost makes sense if you look at that one statement alone.
The seal of the piston is critical. If you remove the lubricants from the gas, the viscosity of the mixture becomes lighter and more prone to vaporization. With a lean mixture, there is less oil to seal the rings. The sealing of the rings has more to do with the performance of the engine than the possibility of having better-burning gas with an ultra-lean gas/oil ratio.
The old fashioned two-stroke oil that was on the market years ago, was designed to be run at 20:1 and was basically petroleum with very few additives. Then, when high-performance oils came along, they cost more to make and sold for a higher price. They got into these high mixing ratios in order to justify the higher prices.
So which ratios should two-stroke gas/oil should be mixed? A properly jetted engine will run better, last longer and develop more power at a lower gas:oil ratio than at a higher one. But what is the proper amount, and how do you know a quality oil from a bad one? The ratio a rider should use in his two-stroke will depend on the size of the machine and the type of riding being done. An 80cc racer will require much more oil in the mix than a 500cc play bike. The best bet is to consult the owners manual and follow the advice of the engineers who designed the motorcycle. As for which oil to buy, that depends on the type of riding being done. Someone who races will require a higher-quality oil for its superior ingredients and properties, than someone who only play rides and doesn't put a lot of strain on his engine. A good, high-quality oil will cost more money than a poor-quality oil, because of the higher cost of ingredients, such as synthetic diesters and ash less detergent dispersing packages. Quality ingredients cost more money, and that makes the quality oils more expensive.
Our advice then, is to buy a quality oil and run it at a moderate ratio. We've used 32:1 for many years. In race bikes that are ridden hard, we might go a trifle richer at say @ 28:1. For a trail bike, 40:1 would be the way to go, assuming that you used a quality oil. If you own a mild-mannered bike, consider a 50:1 ratio.
One of the things you should do, is run high octane gas with any two-stroke mix. When all of the two strokes (the old days) were developed, they all used Castrol petroleum oil at a 20:1 ratio and found that 92 octane gas had the octane reduced to 72 with presence of that much oil. Modern oils won't affect the fuel quite as much, but if you started with 86 or 87 octane regular fuel, you can see where you'll end with a very low octane mix. You could end up with a "pinging" bike.
Race gas? You don't need it in your two stroke unless you're a pro or expert, and most expert level riders are on the new generation four strokes.

Use only two stroke engine oil in two stroke engines. Do not use car engine oil like SAE 10W-30, or the like. Two stroke engines burn oil and are designed to do this, and require the proper oil in the gasoline. Mix the gasoline and oil thoroughly. One method is to take your gas and oil can to the gas station and mix right there at the pump. Fill the gas can about 1/3 full and then add the proper amount of oil, then fill the container. The gasoline pumping quite rapidly out of the nozzle mixes the oil and gas together quite well.
Shake the gas can vigorously before filling your gas tank. The oil must be suspended evenly in the mix, so the engine gets lubricated evenly. If the oil is not mixed thoroughly, the engine starves for lubrication, and the spark plug gets oil stuck on it.
Gasoline is also important. Head for your manual for types of gasoline and octane rating your engine requires. Some older engines require leaded gasoline. Most of the newer engines run on leaded or unleaded. Once gasoline is mixed, use it. Don't buy 10 gallons of gasoline and use five gallons. Gasoline allowed to sit gets stale and gummy. This gummy stuff sticks to carburetor parts and air passages, which eventually will restrict air flow, thus changing the air-gasoline mixture.
All the major manufacturers produce two stroke racing engines in their off-road motorcycles. Virtually all of them recommended 20:1 or 24:1 mix ratios [of mineral oil]. What the actual factory mechanics did at racing events was very telling. Their teams (admittedly not running "stock" engines) but were running engines putting out even more power for the displacement class, followed the same rules.
1) The higher the RPM's the engine turned, the more oil they ran in the fuel. (e.g. a 125cc machine that routinely lived in the 10,000 - 13,500 rpm range ran 20:1 or 24:1 -- The 250cc engines that ran between 6,500 and 9,000 rpm ran 32:1 or 40:1, and the Open Class machines (251cc and up by AMA, but they were all 400+cc engines, usually 465's, 490's, or 500cc) ran 50:1.
(2) Additionally. 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 both 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.
(3) A second test they performed was to run synthetic in 2 identical engines and one was run at 24:1, 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.

One small point. No one ever broke an engine by using too much oil [although it does produce more spooge].

Pre-mix Ratios and Power Production
(unknown source)
"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."

from Klemm Vintage
In short, these tests showed that the oil-presence in the engine is a function of the operating rpm. That is, the "oil-presence" inside a two stroke drops significantly as the operating rpms increase. What this means is that an engine being run at 4000 rpm can maintain a very healthy and happy level of oil-presence with a 40:1 premix. However that exact same engine being run at 8000rpm needs to have a 20:1 premix to maintain the exact same level of oil-presence inside.
It's important to understand that there is no such thing as a "straight petroleum" oil, nor a "synthetic" oil.... those are just industry "buzz" words. With the exception of castor bean oils, all 2 stroke oils are a mixture of the chemical components needed to do the respective job at hand .... and it has been that way for many decades. In the 70's a very common component of most 2 stroke oils was "bright stock". Bright stock was very inexpensive, and offered decent lubrication qualities, but it contributed greatly to excessive smoking, no matter how lean the oil ratios got.
Nowadays, most "quality" two stroke oils have long since replaced bright-stock with Poly-Butane [synthetic]. Poly-butane is roughly triple the cost of bright-stock, but it smokes much less, and still offers great lubrication qualities. All that said, there are still several 2 stroke oil makers that use bright-stock instead of Poly-butane ... simply to cut costs. The bummer is that there is no labeling that allows you to know which is being used, and very few oil makers that will give you an honest answer if you ask them. This same scenario applies for several other primary components of current 2 stroke oils. But There's more.....
99% of all two-stroke oils containers say "smokeless" or "low smoke". The truth is that there is no engineering nor industry standards for varying levels of "smoke-free-ness". The oil makers can print anything they want on the bottles without ever having to meet or comply with any industry standards or limits.
In the genre of Maxima 2 cycle oils, their 927 castor oil is by far the best for high-temperature competition engines.
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Cylinder Wall Temperature Measurement in an Air-Cooled Two-Stroke Cycle S.I. Engine
-Cylinder surface temp increases as the fuel/oil ratio increases but only by a few degrees.
-Cylinder surface temp increases with engine speed.
-A higher oil viscosity is better at preventing piston seizure.
-recorded temps: 201ºC at top of cylinder and 185ºC just above exhaust port.

Here's an illustration from another research paper showing temps of an air-cooled engine at 2700 RPM:

Here's some more online quotes:

"It was shown that minimum friction occurs for cylinder liner temperatures in the range of 140-150ºC, with the higher contribution being due to viscous friction (due to oil viscosity). However, at the higher liner temperature range of 160-170ºC, asperity friction (due to surface roughness) accounts for the main contribution to the total generated friction. It is clear that an increase in lubricant temperature, governed in the most part by the liner surface temperature reduces the viscous friction."

"To a large extent, the cylinder wall temperature also determines the lubricant temperature in the contact of the top compression ring"

" air cooled motor, the cylinder walls of which are at a temperature at least 100º higher than that of a water cooled motor..." [100ºF = 55ºC]
Horseless Age: The Automobile Trade Magazine, Volume 32, page 820

"...fuel, a large part of which is so non-volatile that it will not vaporize until it contacts with the heated cylinder walls"
Automotive Industries, Volume 20, page 653

-The piston ring and cylinder wall interface is generally the largest contributor to engine friction ...which contribute to engine friction to approximately 40-60%
-ethanol is hard to vaporize due to its high heat of evaporation compared to gasoline
-flash temperature parameter (FTP) is a single number that is used to express the critical flash temperature at which an engine oil will fail under selected conditions.
-Although bioethanol fuels have slight impact on the frictional characteristic of the oil, it has significant differences in the amount of wear [due to their not readily vaporizing on the cylinder wall and therefore diluting the oil]

Not all oils of the same viscosity are equal from the standpoint of volatility (risk of evaporative loss). Some lubricants may exhibit as much as a 50-percent greater loss from volatility than others. This is influenced by the base oil's molecular weight distribution. Of course, temperature plays a key role. A low liner temperature translates to a low evaporation rate.

Synthetic motor oils have a natural advantage over petroleum-based oils when it comes to volatility. This is because synthetic oils are designed to have uniform chemical structures. This eliminates the extra chemicals and hydrocarbon structures found in oils based only in mineral stock. Because they contain less lighter chemical portions to boil off, synthetic products lose less of their lubricating abilities to volatization.

API Group I and II base oils exhibit the same viscosity index range of 80 to 120. The breakthrough in producing API Group 3 oils (petroleum derived "synthetic") came when it was realized that severe hydrocracking would produce a base oil with a viscosity index above 120. This was now comparable with the viscosity index range of PAO synthetics. PAOs, categorized as API Group 4 base oils, are initially derived from ethylene, which itself is a colorless, highly flammable hydrocarbon gas. Esters, made from an oxoacid reacted with a hydroxyl compound such as alcohol or phenol, belong to API Group 5 base oils and have excellent lubricity and high temperature resistance. They are more expensive than PAOs and not commonly used as the base oil for synthetic motor oil but rather as an additive. Synthetic oil generally has lower levels of additives compared to conventional motor oils. Most notable are reduced quantities of viscosity improvers because of the inherently high viscosity index (VI) of synthetic oil. A high VI means that synthetic oil loses less viscosity when hot. Synthetic oil generally has a lower pour point so needs lower levels of pour point depressants [solvents] than conventional oils, which have high levels of waxes that solidify at low temperatures. The lower levels of aromatics also benefits the oil as lower levels of sludge dispersants are required. One additive that is necessary is a seal conditioner to ensure seals retain their elasticity and do not dry out, and additives are also needed to disperse products of combustion such as soot.

The volatility characteristics of synthetic base stocks are superior to typical mineral oil base stocks. All the synthetic base stocks displayed greater viscosity indices than did mineral oils. Although synthetics appeared no more resistant to oxidation than did mineral oils, fewer sediments, deposits and fluid viscosity increases were observed with synthetic base stocks.

Castor plant oil (processed through epoxidation) reduces more than 50 percent of smoke compared to petroleum-based two-stroke engine oils
Singh, A., Castor oil-based lubricant reduces smoke emission in two-stroke engines. Industrial crops and products, 2011. 33(2): p. 287-295.

My recent story: My air cooled 100cc street bike revs up to 9000 RPM. It has an iron cylinder sleeve. I was using SynPlus by Amalie at 25:1 with E25 gas and the cylinder quickly wore down so that there was much piston rattle and a big ring end gap. Now I realize that you have to use an oil that is specified for use with ethanol, otherwise you have to use a lower fuel/oil ratio for more oil since alcohol doesn't rapidly evaporate on the cylinder and so dilutes the oil for less viscosity. Now I manually remove the ethanol and I'm experimenting with different oils. The Amalie oil, like most all the other oils, didn't offer any good guidance on what fuel/oil ratio to use which is what inspired me to make this page and my oil ratio calculator spreadsheet. After reboring it with a new piston/rings I used a 50/50 mix of Motul 800 Road Racing and Bel-Ray Mineral Oil at 37:1 which is what my spreadsheet recommended. It was OK but then I changed to a 25:1 ratio and got a noticeable increase in power although carbon deposits on the plug were significant after only 200 km.

Here's a post from the Thumpertalk forum that is very insightful:

"This isn't exactly a scientifically conducted test, it's just my opinions and observations about several different oils that I have tried over the last few years, on both my KX250 and my KDX250. All of these results are obtained running a 26:1 ratio, with jetting as close to perfect as I am capable of. Each oil was used through the life of at least one top-end. I only use Wiseco pistons and rings.

Golden Spectro: This oil did a good job of protecting the piston and cylinder. The piston was a little shiny on the intake side, but wear was within specs, and the piston and cylinder otherwise looked OK. There was a good coating of residual oil in both the top and bottom of the engine. It is a dirty-burning oil, however. It leaves a lot of carbon deposits on the piston crown and head, and really gums up the ring grooves and the power valves. And this oil spooges a bit too much. No matter how sharp you try to jet, the spooge simply can't be completely eliminated. I wouldn't run this oil again unless I had no alternative, it's just too dirty. As a side note that may or may not be related to the oil, this is the only pre-mix that I have ever had an engine failure while using, with the thrust-bearings on the KDX250 crank pin seizing. It was probably just a fluke, and I can't pin it down to lubrication failure, but it's always stuck in my head.

Maxima Castor 927: Very slight scuffing on the intake side of the piston, but over-all everything looked good. The ring grooves had slight deposits, and the piston crown and head had slight build-up that was well within reason. The power valves were gummy, but not to the point of seizing or failing, again within reason for a non-synthetic oil, and excellent for a castor-based oil. Both the top and bottom-end of the engine were very oily and well-lubed with plenty of residual build-up. And the smell of this oil is wonderfully sweet, better than any other oil I've used. I liked using this oil just for the smell! Overall a good oil with no real bad points.

Redline: This was a strange oil. The piston and cylinder looked good, with minor shiny spots but no scuffing, and everything was reasonably clean and well-lubed. But this oil actually left surface rust on the crank wheels, and tarnished the carb brass. It also had a tendency to gum up the carb jets for some reason. How a metal surface can be both oily and have rust on it is beyond me, but clearly this oil lacks any proper corrosion-inhibitors, or it is so rich in esters that it absorbs huge amounts of moisture from the air. I would never use it again, nor could I recommend it.

Mobil 1 MX2T (Racing 2T): The piston and cylinder looked great with this oil. No noticeable shiny spots or scuffing on the piston at all. The top and bottom of the engine were well lubed with plenty of residual build-up, and even the power valves were oily and lubed. No other oil that I've used compares to the cleanliness of this oil. The piston, head, and power valves were nearly spotless, the valves didn't even really need cleaning. If I were a serious racer, this would be my oil of choice. The only reason I no longer use it is the awful, acrid-smelling exhaust it produces. Since I just play-ride with my buddies, they all complained strongly about the smell when they were riding behind me, and my brother-in-law went so far as to tell me he would ban me from riding with him if I didn't change oils. (Edit: this oil is no longer available)

Yamalube 2R: For a dino-based semi-synthetic oil, this is an exceptional product that performs as well as any full-synthetic out there. The piston and cylinder always look good, with no significant shiny spots or scuffing. The ring grooves, piston crown, and combustion chamber were very clean, with only a light circular carbon pattern on the crown and head. The valves are almost as clean as with MX2T, although not clean enough to not need removing and cleaning. The top and bottom of the engine are always well lubed with plenty of residual oil, even on the power valves. This is my oil of choice, and I whole-heartedly recommend it to everyone, racer and casual rider alike.

Here's one of my posts on the Thumpertalk forum:
All big business is corrupt because what they mostly care about is making lots of money, much more than doing whats right by the customer. This chapter of my story is a case in point. I was shocked at how little "disclosure" has been made by the engine oil makers and so I studied up on the subject of fuel/oil ratios in relation to engine oil characteristics and made a spreadsheet calculator that used an oils viscosity to calculate the minimum oil needed depending on different factors such as type of engine cooling and max RPM. Then sharing this discovery on this forum attracted "mototribology" who in his signature says that he only cares about threads talking about engine oils. Obviously to have only one interest in the motorcycling world means he probably has some connection and vested interest in the engine oil business. But that was just speculation on my part. He then started countering every idea I presented about oils I got from my studying the subject and using my logic to come to some conclusions. He even countered a statement I got from his own web site! And he never gave any references to back up his statements. Probably he thought people would believe him since he has a website dedicated to the topic of engine lubrication. But why does he have that site? Is it just because he likes the topic or does he have some monetary interest that would want him to counter my revealing of industry secrets? Well in another thread on this forum he admitted "Companies like mine and our competitors are not going to tell you the formulas or divulge more information than necessary for the most part. We generally like to keep these things to ourselves." to which I replied "thank you for being honest to admit you are part of a controlling system that treats people like nothing but a puppet to be manipulated and used as a "customer". That explains why you are acting to confuse the readers here and contradict me although my formula has already proved itself by showing agreement with other recommended ratios. You are otherwise known as a "disinformation agent"." Then upon looking through his site I found the reason for his wanting to discredit what I'm revealing. He wrote: "My name is Andrew and I am the product formulator and manage the technical aspects of the powersports line for a major lubricant manufacturer." (
So he admits his involvement with an oil company and that they want to keep the truth hidden. I'm giving my information to the general public to empower them. Knowledge is power. The fact that he's come against me is evidence that I'm on to something, especially since he admitted that the oil companies are "not going to tell you the formulas or divulge more information than necessary".
Now comes the fun part, guessing which company he works for. Since he jumped right in with full force on that other thread once I said that the H1-R oil of Bel-Ray is not very good then I figured he works for Bel-Ray.
So here are the claims I made which he slyly tried to refute:
1) Oil viscosity is the main aspect of it that enables it to protect engine parts
2) Viscosity Index is high with synthetic oils and low (under 120) with mineral oils
3) Viscosity index should be high in an oil used in a high RPM high heat engine

The next post on the forum was someone saying that mototribology's full name was Andrew Hodges and that he does work for Bel-Ray.

2 stroke oils OK for premix and injectors:
Spectro 2T, Motul 510 2T, Motul Scooter Expert 2T, Lucas Semi-Synthetic 2-Cycle Racing Oil, Bel-Ray SL-2, Shell Advance Ultra 2T, Maxima Scooter Pro Oil, Motul 710 2T, Motorex Power Synt 2T, Motorex Cross Power 2T, Silkolene Comp 2 Plus, Repsol Moto Off Road 2T, Repsol Moto Racing 2T, Royal Purple HP 2-C synthetic oil

If you have any comments or questions I can be reached via email at