I built the .10 stinger years ago and installed a ASP .12 and it flew very agile. Didn't need any more power. I would say the weight of the .25 would cause other problems such as increased wing loading. I , however , am an advocate of OVERPOWERING. The engine was a ball bearing model. My .40 Stinger will receive the YS .63 since I have it already. kbailey45, I would spend the extra $50.00 and get the AX. Great engine and you will appreciate the power later on IMHO. Also, the Lanier hats are nice. My son has claimed mine (I got grease on his Cabellas hat) so I may have to order another Lanier!!!!!