Absolutely amazing! I'd love to have your machining talents.
Since the topic is about being scaled down, I thought I'd share a pic of the worlds smallest production (now out of production) engine. It's a COX .010 two cycle glow model airplane engine with a displacement of .00997 c.i.d. / .163cc.
It spins a 3"Dx1-1/4"P prop at 27,500 RPM and runs on a mix of Nitro methane, alcohol and castor oil. I used a quarter for size reference.
Shawn