ORIGINAL: Chris-B-chips
my 50 with 5% and a 12.25x3.75 is doing around 14500 rpm. but it needs a lot more power for hovering with that prop.
Why so stingy on the nitro? Both of my SX 50s are roaring like lions on Wildcat Xtra Premium 15%. I run both the 12.25x3.75 and the 12x4 props. I have one mounted on a Model Tech Magic Xtra 300 and another on a Sig Ultimate Fun Fly -- this engine is super-powers both birds.
The Sig Ultimate below shows an OS FX .46 -- that engine finally went south after 3 years of heavy use; I replaced it with the OS SX .50 (no mods needed for engine mount or even throttle linkage). The change in performance was immediate on the 1st flight this past weekend.