Pat,

Shemp is correct about the age of the engine. It came out in the mid-1970's. There were two ratios, but we don't have any information on those engines. They were discontinued long before we became the O.S. Max service centers. We only have information on when they were sold, and nothing else.

As far as we can recall, the gear units were never sold as separate items, but only in conjuction with the .61 FSR engine.

We're sorry, but we'd not know what props would be used. Probably something around 15"-16" in diameter.

You can check the ratio by counting the gear teeth. This would then allow you to calculate prop RPM. The .61 FSR could easily turn 14,000 RPM, The 1.895 ratio stated would give you a prop RPM of about 7,400. Any prop that would turn this RPM on the ground and fly your model is a good one.

Please, though, check the exact ratio of your prop unit, and then calculate the estimated prop RPM before you use the unit. If you accidentally under-prop the engine, you'll over-rev it, and parts for the .61 FSR engines are very scarce.