I have twp of the Byron reduction units with the big four blade props and there is a little confusion here about the systems. The 4.2 Sachs purr power engines were direct drive and were used in the Corsair and the P-47 and the F6f Hellcat. The Corsair and the Hellcat both got three blade props and the Thunderbolt got the four blade. There were some early reduction units in the P-47 that had an idler pulley to tension the drive belts but there was a lot of problems with that system and it was discontinued. The Mustang reduction unit worked pretty well with the Quadra 42 and was under powered with the Early Quadra 35. I have the Quadra 42 and I upgraded it to the Byron Mustang 50 when it came out and Byron produced a kit to do it. It included the two support plates and the clam shell supports for the two tubes. They were made out of aliminum and not the hard plastic of the originals. The Mustang 50 definitely produced more power and spun the prop faster but the static thrust it developed was actually less than the Quadra 42 because it caused the blades to flatten out. Any speed above 3800 RPM on that prop produces less thrust and the blades are the problem. They are soft and they were built that way for survivability but that makes them very inefficient. We had a big forum topic going here a few months back on the prop design and all of the problems with it and a guy in California said he could build the blades out of Carbon Fiber and bring this prop into the modern technology we have today. Lots of guys expressed great interest in the project and then someone started saying it would be a copyright/pattent infringement and he would face a lawsuit from Iron Bay the new owners of the Byron kit line. He said he didn't need the hastle so the forum thread ended. I'm not a lawyer but I sure don't see any infringement in making a prop blade. Are Zinger or Clark or Bolly specifically licensed to produce their props. I don't think so and it just gives the modeler another choice. I don't get it. If a guy was producing that drive system as it was designed by Byron and selling that I could see the problem very clearly. I have replaced the bearings in my reduction system twice and I bought the bearings from Bearings Inc. Is that an infringement?? I buy the replacement belts directly from Gates. Is that a problem??
Making this system work focusses on upgrading a design from the mid 1970s. Prop technology has come along way in that time and it would dramatically improve the reduction system efficiency.

I'm the biggest fan of scale props there is but I know the limitations of what is curently out there and it would be impossible to direct drive a prop of this size with a 3.2 cu in motor.
I agree that the 3.2 makes good horsepower but it doesn't have the needed torque and it develops that peak horsepower through high RPM and that won't work. I don't think you could keep the blades attached to this system at 6500 RPM.

Just my two cents worth.

Jack Devine