Pault: I have all those engines mentioned, except the 72 (plus a few more) sitting NIB waiting for planes that I have yet to build. I have weighed them and used this info and what RCM and MAN wrote in my posting comparison. Many of us in the Hobby are well enough informed to know that HP ratings vary widely (Thanks Maverick) and should be used as a guide only. The weights listed by the manufacturers and/or distributors are rarely correct and often fudged somewhat to their advantage. I and many others discovered this fudge factor a long time ago. Get a scale and check it yourself but make certain the engines are NIB first. The proof is in the pudding when Clarence Lee posts RPM figures and its no wives tale when comparing the Saito 72 vs the OS 70 as the 70 is clearly more powerful. Lee's weight of the 72 was 17.8 ounces, the 70 Surpass 9plain first version) weighs 20 ounces exactly (my scale and USPS's as well) and the Surpass 70 MKII weighs 20.4 per C. Lee. The OS 91 Surpass (the plain first version) weighs 22.1 ounces (my scale and USPS's) with the Saito 91 weighing 20.9 ounces (my scale and USPS's). Do the math.