[Motorcyclesmack]

I have a 21p 3 blade prop with the 5.7litre 454 (not Magnum) top out speed +- 50 mph per gps runs 4200 rpm. engine seems sluggish or like it has more to give to be at a good cruise speed. If I switched to a 22p 4 blade help? I tried a 24p 4 blade just for fun once and I got no change in boat except slower lift out and top speed at lower rpm but it was too low. Looking for a little more speed but rpm seem to low. Live in Cincinnati.

[ColoradoDiablo]

You got a 5.7L or a 454?
Your WOT needs to be in the 4400 - 4800 RPM range either way. If you go to a 4 blade prop you loose top end speed , but gain out of the hole grunt. But a 22P is still too much.
I'd venture to say you need to run a 3 blade , 19P prop to get you back in the sweet spot for WOT and top speed. It will get you out of the hole a bit better too.
See if your local marina will let you do some "test runs" with different props. Hard to come by anymore , but some still do that.
I think most members with your setup are running a 21P , strange.
Do you have a lot of extra weight in the boat like gear , and a lot of people onboard?

[mikeyt]

Larry's pretty much got this one covered. A 19" 3 blade or maybe a 20" - 4 blade SS prop should help solve your sluggishness issues. Going up in pitch will only make the sluggishness worse.

[Motoxxx43]

My 250 came from 2,200' with a Mirage 19p. Not sure how it ran WOT there. I boat at 4,700' with the same prop. The boat will do 50-52 at 4600+/- a few RPM. I tried the 21p Mirage and ended up at 4100-4200 and it was a dog. Top speed was not the same either.

I assume you have the 7.4 MPI which came in the Shabah250s along with the 454/502mag. You probably have the 1.5 ratio outdrive as well which would make it the same setup I have in my boat. Aside from elevation they should run close to the same. I opted to not mess with the prop. It runs good, Ill keep it that way.

[ShabahZ280]

I had the same issue with my Z250. She'd never break 4200 rpm, when a lot of things I read was saying the sweet spot was around 4600. I thought about switching props, and even sending the ECM out to be flashed so the RPM would top out at 4600, but I gave up after a while. I eventually just decided it was much easier to stay out of the high RPM's and save my $$ for fuel. I'll tell you what I told everyone I met on the Ohio, and Lake Erie while I had my Z250. "It looks fast, but it isn't." If you want a boat that'll do 50+ all day long, you'll need to step into a true performance boat, ie Baja, Fountain, Cigarette, Donzi, Powerquest, etc. Mariah's were built for luxury, not speed.

50MPH is plenty fast for the Ohio, if that's where you do the majority of your boating. I've seen more than my fair share of partially submerged objects floating down that river that I wouldn't want to hit above 50mph...