Byron f16, yellow A4, Byron A4 both byrons have rossi 81s little A4 os77 found the larger size won't hit the rpm range and when they do they wont stand up too long, my os 77 on the dynomax will spin 22,500 with a custom con rod, the rossis both have os carbs and are work horses pushing the big Byron fans around 19,000 rpms. The biggest secret is keeping the plane as light as possible at only 11 to 13 lbs thrust it is nice to keep them 11 lbs or under, and if the f16 flames out it will glide a long long time with no bad habits...... oh ya 5% nitro 18% oil some castor..