ORIGINAL: yellerchamp
....For the money the st 51 would be hard to beat, I run a 11x7 prop and love them both.
Yeller,
There is a recent thread here, suggesting the ST recommendation for the 11x6, as the largest usable prop size for this engine, results from the torque curve having a noticeable dip, resulting in 10,700 RPM on an APC 11x7.
...I see Cyberwolf's post, claiming his son's engine spins an 11x7 at 14,200-14,500 RPM...
Since this is typical of most low-to-mid 80s piped .61 F3A angines (Rossi, YS, Webra Racing, OPS, Picco...).
The calculated
actual output is (APC) 1.74-1.85 HP...
I believe Cyberwolf must check his tachometer...
This engine is capable of these number on a 10x6, however.