[elhigh]

I'm pretty sure extra weight flopping around isn't going to make an engine run smoother. Buyers are woefully unimpressed by fuel economy, but they sure do complain when their engine feels rough. For a long time that was a really strong selling point for straight sixes.

I think such concepts as the Crower Six Stroke are a better approach, taking the cooling effect of the water and appropriating its steam expansion for power production.