Here are some actual numbers on the Fuji 50(46.5cc) from a thread on another site (they were posted by a well known engine builder):

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RPM...7100 with a 20-10 Master Airscrew black prop
6300 with a 22-8 Mejzlik carbon prop
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As a point of comparison a new Taurus 2.6(42cc) turns a Zinger Pro 22X8 at 7200RPM, 22X10 at 6480, and weighs 4lbs 1 oz with muffler, mount, and CH ignition while the Fuji weighs 5lbs. (Brison 3.2s and BME 50s have similar numbers to the Taurus - all these weights are actual, not manufacturer's bare engine claims - I have not tested with the Mejzlik, but it should have a similar load to the Zinger Pro, or less)

So why buy a Fuji? There's only one reason I can see; if the price is the most important element of your decision. $399 for the Fuji and $529 for a Taurus(and bit more for BME 50 or Brison 3.2), or how about $410 for a ZDZ40, which still outperforms this motor in all areas. For me that difference is meaningless considering the major benefits of the other high-end engine choices, but I know that is can be a very important consideration for some people.....hummm, so in that case, if price is the deciding factor, buy the ZDZ.

Bill