RE: Webra Speed 91 (old)
Mr Hughes,
After two prominent contributors give you the best advice; to use 20% castor oil and 5% nitro, you try to 'compromise with them' by going half way?
Just get some real FAI fuel (no matter from whom), which is 20/80 degummed castor/methanol and add 5% nitro to it.
It may even cost you less than Omega™.
This engine will not like 10% nitro very much...