Jan is not completely wrong on this one. An engine at full throttle can pull a significantly larger amount of stuff off the ground than one that's taxiing. How much stuff is open to debate, and does depend on how clean the area is.

The last time someone decided to break in an engine in this manner at the field it was extrememly irritating to the rest of us. He tried to keep it away by doing the runs in front of the cars, but the endless minutes of an engine running wide open was not pleasant.

My suggestion is if you don't have a test stand that you mount the engine to a piece of plywood that's big enough to securely clamp to something heavy, like a workbench. It's pretty simple to cut the opening for the engine, drill 4 holes and mount the engine with bolts and blind nuts. Do your runs in front of your garage on a Saturday morning when the rest of the neighborhood is making noise with lawn mowers, weed eaters, blowers, etc. You'll fit right in, and who knows, maybe the sound will attract some people who are interested in learning about the hobby.