DJ:

Ir can be done, but the information wont be very good. You mentioned scale, and that's the problem. But not the scale on the gauge, it's the sheer size of the ordinary automotive tool.

You have to remember that a compression gauge is measuring the pressure not only in the engine cylinder, but the piston has to compress all the air inside the hoses and pipes of the gauge unit as well. The auto tool is fairly large, the enclosed volume can be close to the same size as the model engine you want to test. The result of the larger volume within the automotive tool is the piston's having to pressurize so much space that you will never get a reading even approaching the actual compression pressure. The testers made for model engines have a much smaller enclosed volume and are therefore much closer to reading the actual pressure developed.

Bill.