The 2.47:1 looks ideal for a Rotamax engine.
A 70 inch prop will be running at 2600 RPM while the engine
will be running at 6500 RPM for good power.

http://www.autoflight.co.nz/reduction/distributors.php

Weight (EA)      18 kilograms (With starter attached) 39.6 pounds.
Input speed     Up to 6000 RPM
Casting     LM25 Alloy. Heat treated to T6. Cast locally
Output     Up to 160hp


USA RAM Performance  http://www.ramengines.com/
2929 Clinton Rd
Clinton Ohio 44216
USA