Displacer / Cylinder ratio

[Doogle]

Is there a rule of thumb for the volume of the displacer to the volume of the cylinder?

[Ian S C]

Doogle, yes, for a high temperature motor the ratio is 1.5 : 1, going to about20: 1 for a low temperature one, and the Alpha type motor has a1 : 1 ratio. Ian S C ps I see that you are making a tin can motor, the ratio will be greater, I think the ratio on the one that I built is about 3:1

[Doogle]

Ian SC 3:1 , thanks! Yes I am building my first engine, tin can based, but am using different size cans to the ones in the plan.
Once again thanks.

[Ian S C]

You just need a bit of simple maths to work out the volumes of the two cylinders.
The tin can motor has a ratio of about 2.25:1, just went out and bought the motor in and messured it. The power piston on it is proberbly a bit flasher than most tin can motors, it was made for a Robinson type motor that I started building, its a steel cylinder with a cast iron piston. Up to 3:1 would be OK, but 2:1 would be better. Ian S C