I thought the Merlin sound was the sticking point.

At 100' away my engine sound on water is fair. If you raised the boat 100' up, I know the sound would be much weaker due to the " scattering of the sound waves." I really think you need to build a true V 12 engine using about .50 nitro engines mounted on a beam with a central timing gear shaft. Each engine is fitted with a gear to the shaft.

IT will have the right effect with out any other stuff. It will also have plenty of VOLUME.

And LOADS of torque ??