hi i got a new hanger 9 p-51 trainer i have a question about fuel i know to get 15% but should i use castor or synthitic ant advise thanks

That's up to you.

The nitro fuel containing castor oil is normally pink and can leave a brown residue on a hot surface, such as an engine.

The synthetic fuel is usually green.
I and many others use the green 15% MV (multi-viscosity) nitro fuel.

Power-wise I can't tell much difference...

I use CP 15% MV synthetic lube package.

As Frits mentioned, does not leave the brown spots on engine/muffler.

And is much easier to clean exhaust residue off aircraft especially in cold weather.

alvin ,speaking of brown spots on exhoust :toot: :yickes: :unsure: :embarrassed: :hysterical: :hysterical: