One of the valuable tools are engine test stands, I like to make stand alone units that can be placed on the ground and not clamped to anything. The smaller unit was built with two different mounts based on the size of the engine out of surplus plywood and cans. This test stand is large enough to run an OS-91FX engine.

When I was planning my B-29 I put together a unit that could run the 4 engines, I tested both glow and electric, the picture shows the glow version of the test stand. I even put servos on it to control the throttle to see if I could get the engines to sync together.  At the end of this testing I was able to get all four OS-25FP's to sync together but went with the electric power instead.

Fred Cronenwett