Not exactly double the power... a 4 stroke nitro engine of the same size has more torque, but a tad less overall horsepower because it revs out a lot sooner. There are a ton of characteristics in play, not all of which can easily be explained by members of a forum. Are we talking ignition? Or nitro engines? Flat head, ohc, or ohv? Reed valves, rotary valves, or piston port? Does the two stroke motor have a tuned pope? Is the 4 stroke made by rotax? All these things are to be taken into consideration, and all these factors do not really allow the broad "which is better?" question to be answered.