prop

Does it have a 165 h.p., or a 210 h.p. Interceptor in it?

I'm with Ken on this one in regards to the prop being the issue. I'm fairly confident that the original prop on this boat would have been either a 12x13 or 12x14 depending on which HP version of the 289 you have. It actually came in 165 and 190 HP versions as a 2-BBL and 210 HP as a 4-BBL. The lower HP models would have used the 12x13 prop. But even still, to only turn 3300 as a result of too much prop, you'd have to be turning a 12xsomething way high, like maybe a 16" or greater pitch. If you've got a speedo and the boat still runs 38-40+ mph for a 2-BBL version or 42-44+ for a 4-BBL, then I'd say your tach may be off, because only turning 3300 would certainly bring your top speed down significantly.

If the prop and tach are both correct, and the heads have recently been redone, then I'd check the rocker adjustment to make sure one's not to tight or too loose, causing one cylinder to be completely missing. 3300 is close to where you might drop down to on 7 cylinders. Just a thought.

It's pretty simple to determine the diameter of the prop for most any inboard. Correct Craft uses this formula: center of shaft to bottom of hull - 15% of the radius of the arc for clearence. For example: center of shaft to bottom of hull = 7", 7"X.15"= 1.05", 7"X2=14", 14"-1.05" clearence= 12.95", or a 13" prop MAX.

66polyhead
re: correct craft formula

simple - yes. well known - based on the prop size questions here and other inboard sites, i'm not so sure. anyway, thanks for sharing. i've jotted the formula and rational down to file. good stuff!