Selecting Engine Oil By Viscosity

[jaguar]

Engine Oil Manufacturers make racing oil with high viscosity for high protection, and easy street/trail riding oil with low viscosity at a lower price. Keeping with that plan I devised 3 main riding groups and chose oils for each group based on their 200C (392F) viscosity. This high temp viscosity isn't listed by the oil makers. It has to be calculated based on the listed 40C and 100C viscosities. A hot racing engine can have 200C as its upper cylinder temperature.
Why not use a high viscosity oil for easy riding? High viscosity synthetic oil doesn't burn as well as mineral oil and so causes more spooge. Also that characteristic means it won't contribute to power like a mineral oil does. So if I used Motul 800 on my street bike I'd have less power and more spooge. Group 2 mineral oil is actually pretty damn good. Its flash point temperature is only 16% less than that of synthetic oil. I use SynPlus for my street bike and it has extra detergent additive for cleanliness. I know that because it is rated FD. Its two competitors are only rated FB which means they will leave more deposits. The oils I selected for moderate riding are either rated FC or FD. None of the extreme riding oils are FD.
The 200C viscosity range I selected for the 3 groups are under 2.6 for Easy Riding, 2.6 to 3.2 for Moderate Riding, and over 3.2 for Extreme Riding.
One way to tell which group your engine belongs to is by knowing what is the best NGK spark plug heat range for your engine. Under #8 is Easy Riding, #8 is Moderate Riding, and over #8 is Extreme Riding. You know you have the right heat range if, after making sure the main jet is selected to give the best power under load, the color change line on the ground electrode is near the halfway mark.

EASY RIDING (water cooled street/trail) All recommended oils are rated FD for their high detergent level to lessen engine deposits.
Oils made of mostly group 2 oil - Amalie SynPlus (200C visc 1.75) These two runner-ups are rated FB: Castrol Go! (2.2), Spectro Oils 2T (1.97)
Semi-Synthetic Oils - Motul Scooter Expert (2.17), Maxima Premium 2 (2.15), Motul 510 (1.76)
Full Synthetic - Maxima Super M (2.5)

MODERATE RIDING (water cooled MX, air cooled street/trail)
Semi-Synthetic - Bel-Ray MC-1 (3.22), Motul 800 Off Road (3.1), Maxima Castor 927 (2.7)
Full Synthetic - Maxima Formula K-2 (2.88), Silkolene Pro 2 (2.79), Silkolene Comp 2 Plus (2.76)

EXTREME RIDING (karts and any high RPM engines)
Semi-Synthetic - Motul 800 Road Racing (3.63), Castrol A747 (3.55), Redline Allsport (3.54)
Full Synthetic - Repsol Moto Racing (3.41), Motul Kart Grand Prix (3.29), Pro Honda HP2 (3.2)

My engine oils page now lists the 200C viscosity for each oil listed. This is not available on the oils promotional literature. dragonfly75.com/moto/oil.html

 

[jaguar]

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. Don't Ignore Viscosity Index When Selecting a Lubricant

Viscosity of a fluid is a measure of its resistance to gradual deformation by shear stress or tensile stress. Viscosity - Absolute (Dynamic) vs. Kinematic

Viscosity is very important because it affects the oil's ability to reduce friction and transfer heat.
What is Oil Viscosity a.k.a. Oil Weight? - oilspecifications.org

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.
http://www.aijiuyujia.com/best-2-stroke-motorcycle-oil.pdf

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.)

 

[jaguar]

If you are like me you want the best value as well as the best protection. So if we divide their cost by the 200C viscosity then we get the comparative costs listed below. The lower the cost the greater the value.
$3.10 Amalie Go!
$3.82 Amalie Pro
$4.53 Bel-Ray Mineral Oil
$4.72 Amalie SynPlus
$5.15 Bel-Ray SL-2
$5.70 Putoline MX5
$5.80 Yamalube 2R
$5.88 Klotz BeNOL
$6.44 Amsoil Saber
$6.28 Maxima Super M
$6.53 Castrol A747
$6.53 Motul Kart Grand Prix
$6.68 Spectro 2T
$6.89 Red Line AllSport
$7.05 Maxima Formula K-2
$7.42 Motul 800 Off Road
$7.25 Honda HP2
$7.33 Motul 800 Road Racing
$7.91 Repsol Moto Racing
$7.95 Silkolene Comp 2 Plus
$7.97 Lucas semi-synthetic
$8.03 Royal Purple HP 2-C
$8.03 Royal Purple HP 2-C
$8.13 10 Tenths Race Castor
$8.18 Maxima Premium 2
$8.18 Bel-Ray MC-1
$8.22 Silkolene Pro 2
$8.76 Maxima Castor 927
$8.81 Motul Scooter Expert
$8.96 Repsol Moto Off Road
$9.45 Amsoil Interceptor
$9.41 Amsoil Dominator
$9.49 Shell Advance Ultra
$9.52 Putoline MX9
$10.00 Motorex Power Synt
$10.03 Motul 710
$10.19 Motorex Cross Power
$10.40 Motul 510
$10.49 Maxima Scooter Pro
$10.43 ELF HTX 976+
$10.53 Castrol Power 1 XR77
$10.64 Bel-Ray H1-R
$12.05 Castrol Power 1 Racing
$12.35 PJ1 Goldfire Pro
$14.13 Golden Spectro
$20.17 Schaeffer 9000

 

[Rich Rohrich]

Choosing to concentrate on viscosity at fixed points completely ignores a number of fundamental aspects of the additive packages that will ultimately determine the efficacy of an oil in a given application. Tribology , especially in the two-stroke engine space is a lot more complicated than just picking the correct viscosity. While I'll agree you don't always get what you pay for there are lots of important factors that go into the final cost of a quality product that might not always be obvious to us as consumers.

 

[jaguar]

That is true but since all that is undisclosed I don't want to enter into speculation about what a product may have. I'd rather focus on the specs that are disclosed.