AU,
The methodology that Amsoil uses to formulate their lubes has been discussed before, but it's worth repeating....
1) They select an additive package that has already passed all the relevant API and/or ACEA engine sequence tests.
2) They work closely with their additive supplier to further enhance this chemistry. Generally the goal is to improve the extended drain and extreme temp performance of the chemistry.
3) They substitute a well characterized, PAO/Ester basestock for the petroleum or synthetic basestock used as the Reference Lube ("RL"), in the engine sequence tests.
4) They substitute a high quality, shear stable VI modifier for the cheap VI modifier used in the engine tests. Note that the VI modifiers used in the API/SM tests are designed to shear rapidly. This causes the oil to thin out, reducing friction and makes it easier to pass the "Energy Conserving" requirements of the test.
5) They extensively bench and field test the formulation before it is released. For example, Amsoil is currently field testing their new SAE 0w-20 synthetic - look for it to be released within the next 6-12 months.
6) They monitor the performance of their lubricants in the field through the tens of thousands of oil analysis results they collect every year.
Amsoil has used this process for over thirty years and it's a very methodical and conservative approach to oil formulation.
TD