There isn’ t designated ratio…. and the fuel is your choice of C12, MS98, or MS93. The oil is RC3 or RS7, again your choice. You will have to buy fuel and oil with your entry, and you will have to declare the fuel, the oil, and I believe, the ratio, that you are running. This way everyone has the same opportunity to choose the fuel / oil combo that they want. (this allows for the Rotax to run the 93, and the other TAGs to run the 98 )
You should come prepared with a CLEAN if not NEW fuel jug, or one that you know has only had the spec fuel you are running in it. This will help you to avoid any possible chance of it being contaminated with anything that might cause a DQ. If you have one that has been used for various fuels, you are taking a chance. Better be safe and get a new one for only the new spec fuel you will be using.
If you are planning on cheating with fuel, don’t bother…. the CSC is prepared this year, and will catch you.
Hope this answers the question,
Angie