Thanks Airraptor! I have a OS .91 VR DF with the tuned pipe with the Dyna MAX DF unit to go with it, I should have checked the manual to be sure ! Your right it was the rear exhaust .40's for DF's that were in the 2 hp range. So for a .91 vs electric your talking more on the order of 4Kw power system either lots of amps or volts to equal a .91 for example at 14.8 volts (4 cell) your talking 270 amps.

As to the OP's question I think AXI used to publish a chart for their electric motors, compared to glow engines, your best bet is to go for the weight of the finished airframe to determine what your power requirements are with either a IC engine or electric motor.
Keeping in mind that as raptor pointed out, an electrics motor's power is actually not the the wattage that it will take as input, keeping in mind that the power to the prop is anywhere from 75-95% of that figure due to losses in heat and alike.