hello Keith,

about measurement realized on YS engines : I take measurement of rpm that all members of the forum post on RC universe and on F3A.fr. it is interested to see that all measures was realized with APC propellers and it is more simple for me because it reduces drasticlly the number of prop to caracterize in power.for RCGF and webra I used my own measures because I have these engines at homre. after you must know one thing : when your engine runs a prop the power absorbed by the propeller is eqaul to the power provided by the engine, so if you measure the curve power of your prop it becomes easy to determinate the power of all engine just by knowing the dimension of the prop and its rpm. and you can write : where N is the RPM and D the prop diameter and gamma the power coefficient of the prop.
after in my case measurement have been done with a good weather and a temperature near 20°C, it is some classicals conditions.

the difference that you pointed at 7200rpm is justfied by the difference of the prop sized that they run at this RPM . the 170 cdi run a 20x10.5 and the 170 DZ only the 19x11. in the case of the 19x11 the 170cdi runs this at 7500-7600 rpm. 7700 in the case of CPLR engine.
it is interested to see that the 170DZ becomes very powerful up to 8000rpm it is for that reason that the best prop on this engine is the 17x12.
for 2T engines differences is not so great and and at low rpm (under 8000rpm) the advantage is for 2T such as OS or Webra. but in their case they arrived so early beacause the best prop for them is 18,1x11 which run at 7600 7700 rpm in fact 200 to 300 rpm faster than the ys170DZ.

stephane

PS : sorry for my english, I am no native english