[yodaddy]

I tried the email option since the PM feature here doesn't seem to work for me (or maybe I'm just being ignored!)

My 3.7L has the specs on a cover over the carb, and it lists max RPM range of 4200-4600. The 470 and 3.7L are pretty much identical, so I'd think your max would be the same as mine. My motor will rev that high, just not under load with the current prop.

I'm getting 30 mph on gps at 3400 rpm with a 21p, so using the rough rule of thumb of 200 RPM per inch of pitch, I calculate I should be running a 17p, and expect a top end of about 38 mph.