As long as the engine has adequate cooling and the proper oil/fuel mixture I doubt there is any difference between static running and running it in the air frame. When I worked with the university aero design students we did extensive engine testing in a small wind tunnel with the engine statically mounted and never noticed any difference in performance or integrity of any of the engines tested. The engines were tested with fine pitch props run near their max recommended rpm and with over pitched props that really loaded up the motors. You just have to watch the temp, make sure you have a good oil/fuel ratio and what ever you do try not to run it lean.

Like I said I doubt the motor knows it’s statically mounted or sitting in an airframe. Go ahead run it in the stand. One thing to consider is if you get it running perfect in the stand and it runs less than perfect once you install it in the airplane you might suspect there is a problem with your installation. In a test stand its easy to work on the engine without worrying about possible hanger rash to the airplane.

I know guys with hand built motors as well as the odd radial or two that have been running on a test stand for years without problem. These guys just get a kick out of running the things and never intend to put them in a model.

Dennis