Frogman - I was thinking of getting the hull to hit the desired speed - not trying to suggest the most exotic powerplants.

The 140cc QD would not work in the boat any better than a 70cc QD (Not that the 70cc would work all that well). There is a point where you over power a hull. On a Vee less than 60 inches your probably looking at the 10hp mark for most RC motors on the market.

Torque roll from a prop able to use the QD70 (probably a 7516/3 or 8016/3) would certainly want to roll the hull. And if you talk to any one who has powered such a hull with a QD70 you will hear that the boat rolls (not could roll - will roll). The bigger 140cc motor would be asking for a 9515/3 or similar - just not feasible.

Question - how many boats you seen with a 140cc QD ??? I would like to bet it is NONE. Because last I heard QD had sold two of those motors and neither went to a boating application.

The QD70 run through a counter rotating box may work but it is no different to running the two QD35's counter rotating as I listed above.