Martin, you've let the cat out of the bag now!

You've got all the main players in the fourstroke .60 - .91 bracket except Saito. A benchmark test is mandatory: you must put these engines to the test and report the results! You may bust a few myths in the process.

I can tell you from experience that the YS .63S will turn a 13 x 6 at about 500 - 700 rpm more than an OS Surpass 2 .70 can. I've flown two examples of the same model - one with a YS .63S and the other with the OS Surpass 2 .70 and the YS is most definitely more powerful. An OS .56a may get close to the .70 Surpass but it won't match a YS .63.