How to verify gear ratio?

[mtnmatt]

I recently purchased a 106 drive and had it professionaly installed. My boat is a 1974 apollo 18' with a brand new 351w, rollercam, performer intake, 600cfm carb,running 9.0-1 compression, new coil, new electronic distributor. The engine builder claims it makes its peak power at 5,000 rpm. This boat is very light about 1200 lbs. I did my 10 hours of break in on my new drive. I have been doing the short bursts of full speed. The boat does not seem to rev? I initially tried a 21 pitch prop. Then I went down to a 19 pitch prop. Not much difference. With the 19 I can only get 4500 rpm with only me in the boat and trimmed all the way up scary high on the trim. I have tried diagnosing the problem everything checks out. I went to a bigger carb, checked coil, distributor, changed props. Nothing seems to help. This is a 300hp motor by all calculations I should be able to spin at least a 21p. prop and go 65 mph. Close as I can get is 4500 rpm and 56.2 mph. Is it possible I have the wrong gear ratio on the drive? I spoke to sales before ordering and they said I needed a 150 or 147 which ever you guys have so thats what they sent.
Can I verify this on my boat? Or do you think my problem lies elsewhere? Matt Konkol , Spokane Washington. Thanx in advance any help would be appreciated.

[admin]

A 1.47 ratio would be correct for that boat. If you had the incorrect ratio the RPMs would actually be higher as the other ratios are a higher turns of the engine to the prop. Of course the other ratio's are designed for smaller engines, so they would not hold up to your 351.

It would seem to me that there must be an engine issue somewhere.

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