Last time I looked, the "4-stroke" fuel had a lower percentage of lubrication. I have always used Omega fuel for both my 2 and 4 stroke engines, and like the performance and longevity. I have used 15%, but found I did not need the extra nitro, and now use 10%. Some engines (magnum and Supertigre) seem to perform best with 10% maximum nitro. Saito will benefit from higher nitro content, but don't need it to run well. YS engines require 20% nitro with 20% synthetic oil content.