what does the 400 stand for in a 400 motor, or the 300 in a 300 motor?

Those numbers mean as much as the numbers GM uses to identify their trucks, ie. 1500, 2000, 2500.
The higher the number the bigger the motor's power. Look at the 380's, 280's, etc. Just a little less powerful than a 400 or 300. It was the way they numbered their models of motors. I read where one company building electric motors compared them to glo motors ie. 05 meant 1/2A or .049 Cu. In. 10 was about a .10 Cu. In.
15 like a .15 cu in, etc. I'm not sure they even mean anything today, as windings (not always given), wattages(not always given) are used today to describe them. Have you seen the new FLY RC magazine!? Boy! They really covered a lot in electrics.[img]i/expressions/face-icon-small-smile.gif[/img]