Read pages 66 and 67 of Sir Stanley Hooker's biography "Not much of an Engineer". There he explains how he persuaded his boss, Lord Hives (Hs,) to go to see Whitle's gas trubine engine which was developing 800 pounds of thrust. He explained to Hs that the Merlin engine in a Spitfire flying at 300 mph, with a 70% efficient propeller, delivers about 840 lb thrust. Hs then made immediate arrangements to go and see Whittle. Apparently a piston engine in an aeroplane doesn't develop thrust until it starts moving through the air.
That is what I am trying to explain. You can not directly convert one physical quantity into another one. You need at least two independent quantities to combine them for calculation of a third quantity.
Like in this case force * speed = power
The problem is, which "speed"? Power is energy/work per time, so how much energy the engine will deliver to accelerate the airstrem through the engine. Therefore you have to know how much quicker is the air behind the engine than in front of it. This I think is a different kind of "speed" than the travelling speed of the whole machine. Also (being no expert on this) I assume that this speed difference will not be constant for the whole range between "standstill" and maximum speed of the whole vehicle.
Finally, even if you would know this quantity (the acceleration of air through the engine), you would still compare the effective power of the whole set-up of a jet engine to the nominal power given for a piston engine. You could compare it emprically by attaching for example a propeller to the piston engine and then look which revs you need to achieve the same thrust like with a jet engine, but of course you would have a certain loss depending on factors like propeller dimensions or aerodynmic shape.
So I am afraid the answer to your question is "no"...
Edited by Robin Fairservice, 07 January 2013 - 17:16.