We are building a .40 size extra 300 from great planes and we are thinking of either a .61 O.S. or a .81 Saito. The plane will be flown in semi 3D/Pattern so I hope I can get some response on this to help us make a decision.

Thanks,
Flyer 202

Both are good,the Saito will have more response and torque,needed for 3D flying.
The GP 300 will probably not offer any 3D enjoyment though.The Fliton is a bit bigger,but would have had the performance envelope you wanted on those engines.

Now that we are to the end of the wing building stage it is beginning to be a pressing issue to decide on a motor because the fuselage is up next.

Please!!!! State you opinion. I know that the GP 300 won’t be a great 3D plane.

Thanks,
Flyer 202

The OS 61 is rev happy and the exhaust my get in the way.I think its more suitable for a fast warbird or Pattern machine.
Wait for other opinions,but I think the 82 has my vote for all around power.It is content with a wide variety of props and nitro.You can experiment from there.I think the engines are similar in weight??
Perhaps a YS 63 will keep up with power and shed a few ounces?
If wanting to try any 3D the 4 stroke may help with low end thrust and fast spool up for stall recovery.If you havent purchased yet, the YS maybe a real consideration.Dont let the diplacement fool you,it will keep up with the bigger motors.

Stay away from 60 sized engines if you can. The extra weight is not worth it. I have tried this out in a few 40 sized planes for aerobatic flying and its no fun. If you want to have fun for 3D etc then go with something like the Saito 82 or YS63. Is there a Saito 81? If you mean the Saito 80 then between the 80 and 61, weight is no longer an issue as that is all you have and both are about the same in weight.

ps the Fliton Extra 330 is a real superb machine to fly. Tried it with a Saito72 and TT61 2C, the Saito 72 was more fun to fly than with the TT61.