Quote Originally Posted by wobbly View Post
Lodger, part of the answer lies in the introduction of many fully synthetic race oils, they all started to appear around the time that GP racing converted to Unleaded fuel.
Motul 800 Elf 976 etc.
Unleaded is best when operated rich, with less compression and more timing.
Up to that time the most widely used oil was semi castor Castrol 927, in fact I know for sure that many teams with oil sponsors actually secretly substituted this so as not to upset anyone.

In the tests I did ALL the fully synthetic oils LOST power when run in the KT100 up at an EGT of 650*, no matter what the oil ratio was, compared to the HTX 909.
What you have to realise is that all the synthetics, when tested in a Timken/Falex machine, have huge oil film strength, but the instant they loose this film and are overheated, they break down into their component
constituents, that are NOT actual lubricants at all.

The very old R30 castor oil has probably 1/10th of the film strength, but when its overheated and breaks down, those component chemicals still operate as lubricants.
And I know some experts have rubbished the Falex machine as being unrealistic in a 4T, but empirical evidence in a 2T shows exactly the same characteristics as the machine demonstrates.
When a synthetic film is broken down, it tears the shit out of everything, a Castor type fails sooner, but the wear pattern is perfectly smooth on the test shaft.

In the KT100 test at very high run temps, I was seeing really premature piston skirt wear using Motul 800 and several other full synthetics - plus the obvious power losses.
I had used Maxima 927 in the USA with 110 race gas in World Champ Jetski's, as the HTX909 was not compatible and would separate out very quickly.
Both are semi castor mixes, and that seems to be the holy grail in 2T race engines operated out at the limits.
HTX909 separates real quick in AvGas, the Maxima doesnt, but both those oils are perfectly fine in pump gas, or the unleaded fuels mandated for CIK or FIA racing.
Thank you Wobbly. Excellent reply as always