Following non-dimentional numbers is used in this prediction method.
Non-dimentional engine speed, n^*:
Non-dimentional work, W_S^*:
Non-dimentional output power, L_S^*:
Non-dimentional engine specification, S^*:
Design pressure ratio, P^*:
Non-dimentional temperature, T^*:

W_s: Output work in one cycle (J)
P_m: Mean pressure (Pa)
P_lim: Design pressure (Pa)
V_SE: Swept volume of expansion space (m³)
R: Gas constant (J/kgK)
T_E: Gas temperature of expansion space (K)
T_C: Gas temperature of compression space (K)
T_lim: Maximum temperature in design process (K)
: Viscosity coefficient at temperature, T_E and pressure, P_m (m²/s)
_lim: Viscosity coefficient at temperature, T_lim and pressure, P_lim (m²/s)
n: Engine speed (rps)

* When you check 'Use the design and permitted values', P_lim=P_mand T_lim=T_E.

I have reduced the experimental data of Ecoboy-SCM81 and other high performance and low temperature difference Stirling engines.
Following figures show the relation between the non-dimentional engine speed, n_max^*, and the non-dimentional output power, L_Smax^*, and the relation between the non-dimentional engine specification, S^*, and the non-dimentional engine speed, n_max^*. Experimental equations which are shown in the figures are estimeating the characteristics of the engines well.

Non-dimentional output power, L_Smax^* as a function of non-dimentional engine speed, n_max^*

Non-dimentional engine speed, n_max^* as a function of non-dimentional non-dimentional engine specification, S^*

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