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Can anyone tell me if the size (diameter) of the port that allows air into the power cylinder in a hot air engine (e.g. model Henrici, Robinson etc) has any bearing upon performance?

I'm told 25% of the power piston diameter is the number. I've played with this a little but didn't see any real gain or loss from increasing it to about 50% I have seen diaphram engines that are 100% so I'm not sure how this effects operation. A safe number is about 25% though.

Thanks for the reply.

By luck rather than design my ratio will be about 21% so hopefully it won't be a major problem. Once she's up and running it'll be a simple matter to experiment with reducing the aperture although I won't be able to expand it easily.

Thanks again