It sounds great on tick-over, sadly the illusion is lost at high revs. But a fantastic achievement.
I guess there would not be adequate power output at maximum full size speed (1,000rpm) even to propel a scale model along - despite the large flywheel?
I've thought over the years about a scale slow speed engine but never quite got my head around the mathematics/physics of scale power/torque outputs from a miniature engine (anything above 2,800rpm is beyond my comprehension).
You get no joy from running a short-stroke (or equal bore/stroke) modern small diesel at very low speed, I guess a properly miniaturised long-stroke design would fare better?