A good rule of thumb for any size single engine fighter type model is to have one Horse Power for every 5 to 8 pounds of aircraft. This is true all the way from a .40 size model up to the real thing. This is of course a guidline for power-loading and cases outside of the paremeters above can be found but in general if you are within these parameters, you will have a model with the correct power.

The power, not displacement should be considered when choosing a powerplant, in this way you have a target HP first and can choose an engine of the desired type such as: Gas, Glow, 2 or 4 stroke secondly. Also, even though manufacturers (sometimes) overinflate their products performance figures the range I show takes this into account. For instance, a typical .40 size warbird weighing about six pounds flies good on a .46 which in many cases has an average rated power of 1.2 HP. This puts the model at about a five pounds to one horsepower range and the performance shows it while a smaller .40 will fly it more scale like with a loading of maybe 6.5 to 7 pounds per HP.