As far as I know, these are still the same formulation, and both are "JASO MA" rated for use in wet clutches - that's the highest rating you can achieve. Of note,the S2000, 20w-50 racing oil is JASO MB rated, for use in wet clutches. Many of the folks who race motorcycles with Amsoil use the better S2000 stuff, either the 20w-50, or even their 0w-30 to gain more Hp.
Amsoil does not use any borate friction modifier in their MC oils. However, this is a marketing decision as much as anything else. The original Amsoil 10w-40/20w-50 have been used in wet clutch bikes for over 25 years without causing any problems. The type of oil soluble FM's that Amsoil has always used don't mess up wet clutches, period. I suspect this is because they don't chemically interact with organic clutch plate materials. Solid based FM's like Teflon or MoS2 do cause problems, because they mechanically/physically decrease the surface roughness of the clutch plates, which reduces the Cf of these surfaces. (Quite honestly, just thought of that theory as I was writing this, but it makes sense.)
Friction modifiers are added to xw-20 and xw-30 gas engine oils to help them pass the Sequence IV, fuel efficiency test. This test is required for the "SL" and "GF-3", gas engine specifications. A FM will typically increase fuel efficiency by 1%-2%, although it is debatable how long this effect lasts. These oils are only required to show fuel savings out to 96 hours with an engine used on a test stand, which equates to approx 4000 miles of use on the road ....The # of fuel savings required after 96 hours is significantly less than what is required after 16 hours of testing - about 40% less, as I recall.
Tooslick
[ February 15, 2004, 07:39 AM: Message edited by: rugerman1 ]