Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Update:
  .... have some internal drag....

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Fwiw, the o-rings in my engines seem to create more compression with less drag when I mix one part Marvel oil with 35 parts low-octane gasoline.  I've tried motor oils, ATF, and 2-stroke oil and got some drag.

The ratio works well with Naphtha, too, but there is less energy (a softer bang) with that fuel.