Spiral --First off the Omega is 17% total oil of which is 70% syn. and 30% castor. So your fine on castor content. The A3 is hotter than the #8 and colder than the #F . Tune for the #8 which can be had by any LHS in the nation.............If you were at 0% nitro the A3 would be an option....If you can't point plane straight up in the air for 30 seconds and not loose RPM , then your not ready to put plane up..........Millions of engines run OS#8 on 0-20% nitro .. I personally like the Fox RC long at $2.35 a copy with the same heat range as the OS #8 at about $7...............