[douglas]

hi my 1999 z258 limited edition with a 7.4 merc and bravo 3 leg has 22 pitch props bu t will only turn 4000 rpm with a speed of 40 mph does anyone know the factory spec for rpm and prop size what speed are someothers getting with this boat set up thanks

[Motoxxx43]

What's your elevation? I have a 2000 Shabah 250 (similar to the 258) with a 7.4 and a bravo 1. I run a 19p 3 blade at 5000' elevation. I managed to hit 51mph on Saturday at 4600rpm.
Seeing as you are at 4000 rpm you are missing out on 400-600 rpm which would benefit you a few ways. Dropping your pitch would get you on plane easier and get you a little better top end, maybe 45-48 ( just a guess!). You would also use less fuel due to the quicker plane times. Then again, depends on the load in the boat. (Number of people, gear, ice chests, fuel, etc)

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[Motoxxx43]

Sorry to not answer the last question. Your 7.4 WOT should be 4200-4600.

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[douglas]

the elevation is 1200 feet as in the weight one or up to four people the prop is 22 mec 48-823663 and 48-823664

[douglas]

i need to compare the same drive and ratio as my boat is a 1999 shabah z 258 cuddy 7.4 bravo three 2.0 ratio with 3 blade stainless 22 pitch 15 inchs running wot 3800-4000 i only get 38-40 mph at 1100 feet alivation and light load 2 people in boat rpm checked motor fine low hrs and speed was gps thinking of changing the drive to 2.2 ratio if it would help

[mikeyt]

The 2.0 gear ratio is the one normally used in these situations. It might be less expensive to buy a set of 20" props and use those. That will bring your rpms well into the recommended range.