This is an old thread but looks like a good one... so I hope everybody is OK if I add to it rather than start a new one.
My 1979 CVX 18 has the stock Mercruiser 305 228/Alpha 1 configuration, aside from a recent upgrade to an electronic ignition. My exhaust is just a straight tube now (no bellows, more on that later).
With a 4-blade Mercury Spitfire 14 x 21 I am getting max speeds of 50-52 mph regardless of passengers/fuel and otherwise somewhat smooth boating conditions (wind, water etc). The boat is maxing out at those speeds just a shade over 4,000 rpm.
Does this seem about right?
It sure gets out of the hole fast and corners like I'm in a movie.
I won't be pulling skiers, mostly cruising. Are the suggestions above still good if I'm looking for more top end? Any new ideas?
Thanks in advance!!