prop confusion

[full stringer]

ok i have a 350 chevey with a omc 800 stringer outdrive i just changed my omc outdrive upper from a v-8 gearing to a v-6 geared upper the old unit had 21:16 ratio and the new upper has a 21:20 so is geared higher if you will i ran the boat today and with an aluminum 14 1/2 x 19p prop the engine is way over revving.its doing 3000 rpm and only 14 mph with the old set up a 15 x 15ballistic stainless prop and the other upper gearcase 21:16 it would run about 25 mph at 3100 rpms what size prop should i change to a shop said go up 2 inches well i went up 4 and still way to high rpms that motor will turn 5000 rpms right now if i throttled it wide open really need some help on this one??? the boat is a sea ray cruiser weighs 4020lbs dry weight

 

[steelespike]

Re: prop confusion

When you start messing with gear ratios you can take yourself out of the range of available props.And while you may get the rpm under control performance may never be right.I'll assume you need to be at 4,800.If your at 5,000 a 1" change will take you to about 4,800. 2" to about 4,600.