From John's link I found this.
It seems to require data from an engine I would be using for a sound file. How does one get this info if you don't have the engine in hand? I can probably assume driver diameter is the same but don't think I can assume gear ratio or flywheel diameter is the same.
I am upgrading a USRA Pacific. Data for this is Driver Diameter= 1.535", Flywheel Diameter= .827", gear ratio = 16:1
Pete