Guys, 3W makes one awesome engine. The power is unbelivable and is quite a smooth runner. Im also using on in a yellow spitfire only mine is a 60. Im running a scale exhaust and its spinning a 22/12 menz ultra at 7100rpm and is well broken in. Its got more than enough power to really make the spit move and it makes a great combo. The 50 looks shorter and will fit more in the cowl and should give sufficient power also. Just make sure it runs cool warbird_1 and you wont have any problems.
Evan Q.
http://www.homestead.com/evoshangar/home.html