My prediction is slower out of the hole, slower top end at mfg rpm spec
(42mph). WOT RPM probably won't change much due to the larger diameter prop
(pitch being equal). Cruise will be about the same.

--Mike

"Joe Blizzard" wrote in message
...
I've put an aluminum propeller on my '77 Thunderbird 18' tri-hull in place
of the original stainless steel one. Old prop is a Mercury 48-73982A4, 13
3/4" diameter, 21" pitch. New prop is a Michigan Wheel Vortex 992005, 14
1/4d, 21p. It's attached to a Merc 165 I/O. On the original prop, top
speed was 45MPH indicated and cruise was in the neighborhood of 25-30
indicated at about 3200-3500 RPM.

Anybody want to predict what (if any) performance difference I'll see on
Saturday when I take it for a spin?