I bought a full piped GZ .061 from Bill Hughes a couple of years ago and it turned a APC 4.2x4 at 42,000 rpm. That is 700 piston pops per second. The 14 oz. model accelerated out of my hand faster than anything I've ever seen, forget about cavitation. The cost in spent time replacing parts for this kind of performance is high, and parts for this series crankcase are no longer available. The newer GZs must be at least as good as my old one. 42,000 rpm sounds totally Satanic, "unworldly" when it jumps on the pipe. There is roughly a 10,000 rpm jump when it hits resonance. If you want try one out, give Bill a call and he will fix you up.

For about $200, you can get a Cyclon or Fora .061 and run 32,000-36,000 all day on low nitro fuel. these engines are easy on plugs, hold a steady needle, and I've never even had the backplate off of mine, [after 4 years or so of ownership]. On a small enough model, these engines can really produce some excitement.