Rajul-

It depends on the specific brand/model of engine. What do the instructions call for?

For example, I have a magnum 4s that calls for 16% oil, preferably castor. I also have a saito that says 18-20%, but little or no castor. I believe most OS 4 strokes call for 18%+ synthetic, castor or blend. And I believe YS's all need 20% oil.

If your engines have similar nitro ranges and you want to use one fuel for all, read each engines manual, and select a mix for the engine that requires the highest percentage oil using a synthetic/castor mix. This should work ok with all of them unless you have an engine that specifically states "no castor". Extra oil is almost always better than too little.

Remember to always follow the instructions and you should be fine.

-Jeremy