For the prop size to go with steam engines its normal practice to have a large prop with a steep pitch, my understanding of the reasons for this is that steam engines torque is higher at low revs and second but more important in model boats is that with the engine turning over slowly the available steam will last longer - increased run time on the water.
So why depart from that rule of thumb with this engine?
Well unusually, the power curve for this engine is available, indicating max power at 2bar at 3700rpm, so my objective is to find a prop that will allow the engine to rev to that level so that the engine is being used at its maximum - the aim is not to conserve steam or to run for a long time, the aim is to celebrate the power and glory of this wonderful masterpiece of steam engineering. Lets remember this is a 2.5cc V 4 engine, each cylinder is just 0.6cc - thats just mind-blowing.
Thank you to KBIO for providing the additional information and for the suggestion re letting the sump vent to fresh air to ensure that back pressure is not limiting the rpm.
Here then is the performance data for the Saito V4PR Engine taken from page two of the instructions - I think its fair to assume that the performance of the Tribute engine is likely to be at least as good as the Saito V4PR's
Also included is a photo that better shows off the exquisite alumininium exhaust manifold - just marvel at the work that has gone into producing it.
