Comparing just engines to motors doesn't really work. ESC, prop and battery need to be "in balance".

The answer is here:
http://stunthanger.com/smf/index.php/topic,12044.100.html

Cobra motors have a great set of charts available on how much power and RPM with different props that can be used to help size a motor to a model

But the method I use is watts per pound of model, the rule that has proven to work is to have 100 to 150 watts per lb of model, so if I have a 10 lb CL scale model I need 1000 t0 1500 watts of power, then I am good shape.

Then I look at the prop size to make sure it can clear the ground and other parts of the plane if is a twin. Some motors are designed to spin small props while other motors spin larger props. I really don't care about the RPM since I am flying with throttle control.

I ignore the name they give the motor. The battery, propeller and motor combination will determine performance

Fred

Matt-

I pondered the same thing as you did when I got my ARF Oriental and wanted a motor for it.
The safest way is to look through the setup thread, and pick either the same exact motor as someone else used in the same plane (or same size and weight plane), or use a motor that has about the same weight characteristics.

A few observations-

Most folks use a 4S pack for .35-.40 glow sized stunters. A Kv about 860 to 950 should work for those voltage packs, with the higher KV favoring a smaller prop and the lower favoring a larger one.
Some people are using 5S and 6S packs in their larger planes.

A decent rule of thumb is the motor weight should be about 10% of the RTF plane weight (6oz motor for 60oz plane) and be capable of running at 150w/lb continuously.

My example can be found in the "Shocking the Oriental" thread originally started long ago when less people flying electric. I picked a fairly small motor, an Exceed Rocket 3020-950kv, it weighs about 4.5oz. My plane is flying at 48oz, and uses 1650ma from a 2500 4S pack during a 5m30s flight, turning a 10"x5" APC prop. It has plenty of power, and is only drawing an average of 19 amps.
Coincidentally, another pilot with the same plane and same Exceed Rocket 3020 motor, but this one a 860kv, chimed into the same thread, before I got the maiden flight handled. He's using a 11"x5.5" prop with the lower KV, and says his setup works great as well.
I think my motor is only rated for @ 360w, but it works great flying the plane, putting out about 19A x 16(?)V = 314W...
Sooo, at the 48oz weight I'm flying at, I am only using an average of 105w/lb. I'm sure that withe the KR timer I have set to the #4 gain setting, its putting out a little more juice in the climbs, but it seems pretty miserly on the electrons to me.
I hope some of this info is helpful to you.
Good luck in your electrification.
Regards,
Chris