i have a 1999 21ft mariah z212 shabah. got a 350mag 310hp. running a 21 pitch 5 blade prop and its quick out of the whole but looking for more top end. any suggestions would be great.

thanks

How much more top end? What RPMs are you running now at tip end. What kind of prop

How many hours? B1 or Alpha? Wait for rebuild time and build a 383. Add a drive shower, monitor oil temp etc.

Find a lake w/ a marina that will let you water test props. Get a buddy to come along, a GPS and a stopwatch. You drive while your buddy takes speed/time data. You make notes for each prop you test about how it feels from the drivers perspective.

Then make sure you buy the prop from that marina as payment for them loaning them to you.

the rpm is at about 6200 at tip top. andim not sure of the make of the prop. its got 253 hours on it not quite rebiuld time but like the 383 idea. thanks for all the ideas.

its got a b1

top speed is 67mph which is good for a 21ft boat but the key is to get there faster.

You need to find out the rpm range of the engine then prop for the top of the range plus 200rpm. I wold imagine a 350 would be about 5000rpm which means you need more pitch. 3 blade props are usually the fastest.

BT

If it's a stock 350mag, your spinning it way past it's peak powerband at 6200rpms with the 21p. Go up in pitch to get the rpms down in the meat of the powerband.

That rpm seems way too high. Possible bad reading, which is common on stock boat tachs.