Hey Gene,
I mix up what the engine needs based on the engine type, and intended use.
For instance, I make up 10 nitro/ 20 oil for my sons trainer, and I make up 20/20 for my YS engines. I have several engines and only a few of them run the same fuel. My Fox 74's, all my 40-46 size sport/trainer engines, I run 10/20. My older control line Fox 35's I run 5 nitro/25 oil. My YS's and Saitos all run 20/20. My Rossi's and MVVS's all use 5/20 and my big Super Tigers run 3/12.

As a general rule, thats what I run Gene. Are you glad you asked?

Fuelman