I have a BUSA 1/4 scale Sopwith Pup, powered by a Zenoah 26, I have been flying 9 years. The original engine was Zenoah 23, I upgraded to the 26 four years ago. Both engines provided plenty power for me. This is my Pup.
I flew the 1/4 Camel with a G-23 and a 20 x 6 prop. It flew very well. I won "Best Gas Engine Performance" and the special WW1 event at the recent NASA Scale Classic held in Woodruff, SC just last month.