Originally posted by Razor
I flew a TF Mustang with a YS-120 (wish I could remember the prop. :stupid: ) it was quick but not compared to your numbers there...
What prop. would you recommend for pure speed on the 120?
Anyhow, I am not as familiar with 4 strokes as I am with 2- but do you think any 4 cycle could pull faster than a Jett-90?
All these big strokers add alot of weight- 
I have T/F and the Modeltech 1/7 scale Mustangs. These are bigger heavier rmodels, 775 plus sqaure inches and they weigh in at 10-11lb. full house... The WM Mustang is a splash of Great Planes .40 size Mustang. Typical weight with two strokes is around 6-1/2lbs. Great flying models, their a little draggy and they have fully symetrical wings.
We use APC 14/12 - 14/13N at 10,500 with YS SC-120's.
YS four strokes out perform all others CC to CC, hands down. Different kind of power for sure. Much more torque and low end grunt.
I have a Jett 76, Dub modified it for warbird racing with a bigger carb and changed the timing slightly. Were limited to displacement on our models, .75 two strokes need 575 square inches while .91 four stokes can be as little as 440 square inches.
The Jett 76 and 91 pull an APC 12/6 at 14,300 and 14,700 according to Jett. Lot's of static thrust but not much in speed, around 83 mph theoretically.
Anyway I have tried the Jett .76 on the same WM Mustang, the Jett makes a lot of noise and sounds like its busting a move but it's not as fast as the YS powered model.
The two strokes won't carry the pitch, so they don't go as fast. These engines are port timed for RPM, lugging them down with high pitch props cooks em, smaller props with high pitch to maintain RPM requires a lighter less draggy airframe to work as less static thrust is available. Not really feasable with this Mustang...
YS 91-100's weigh in at 25ozs.
YS 120's weigh in at 32ozs.
OS61-91 weigh in at 19ozs. less the mufflers.
Jett .76/91 RTF weighs 25ozs.