I have a 1988 39' Sea Ray powered with twin 454/340h.p. Mercruisers with 1.88:1 gears turning 18"x16.76" props; max rpm = 4500 . The boat cruises at 3300= 16-17.5 knts W/full fuel. I would like to get a faster cruise speed 19-20 knts. Would 2.5:1 gears help/hurt my cruise with new larger...
