Off shore donzi

Yngdmax92

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Sep 26, 2013
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Looking for some direction here. I know it's coming soon as my brother keep talking about it, but he purchased a 1998 zx 22 step haul 454 mpi (not mag) 2 years ago and is upset that it doesn't go over 60. So.... Instead of upgrading the engine to. 454 mag, or A 496 or 502. Thinking were going to rebuild this one. That's where I get a little lost. It's marine, and it has the Delphi ignition. Maybe, just maybe some people on here can point .e in the right direction to steer towards some body who has some experience with building these 454's and tuning them. I can put the engine together, but what to put in it and where to buy them are the questions I need to have answered.

Thanks in advance!
 

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
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Needs more rpm, try going to a smaller diameter prop before you rebuild, sounds like there is too much load on it as it is propped.
 

Yngdmax92

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Sep 26, 2013
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Needs more rpm, try going to a smaller diameter prop before you rebuild, sounds like there is too much load on it as it is propped.
this is not a mag though, i read that it is only suppose to run 5100-5300. its only a 310 or 330 hp 454. i just think the boat needs more power. yes it is a stepped hull but donzi's are generally heavier then the other units i am assuming
 

Yngdmax92

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Sep 26, 2013
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okay hold on fellas!!! my notes are off. just looked at them.

19p three blade prop - 4400rpm 51mph
21p three blade prop - 4200rpm 53 mph
23p three blade prop - 4100rpm 53 mph

the other info i was using for rpm and speed was for a 350mpi in a donzi z23
 

THEFERMANATOR

LEGALLY INSANE
Feb 16, 2009
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Stainless or aluminum prop's? What leg is it running? How does it ride? Does it need alot of trim ir does it like being run trimmed all the way in? The carbed low output 454's I don't think liked to turn many rpm's(4400 IIRC is about it for them). Propping is a science, pitch is just a number, you need to also know gear ratio to figure prop slip. The last boat I propped was a 26' SeaRay, we went from 21p 3 blade stainless props to 18p 4 blade stainless props, and gained speed everywhere, greatly improved the holeshot, improved economy, and actually reduced cruise & wot rpm's by bringing his prop slip way down and getting props that would lift the bow up.
 

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
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You can go down in diameter and up in pitch and still have same load the slip will just go up. Like Ferm said it is a science, I use The Prop God a good bit. He has setup more boats than anyone except Reggie Fountain, and if you can't figure it out Reggies original offshore powerboat riggor lives in Wilmington and owns Marker 17 marine, Brian knows his shit...
 

Yngdmax92

Member
Sep 26, 2013
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Stainless or aluminum prop's? What leg is it running? How does it ride? Does it need alot of trim ir does it like being run trimmed all the way in? The carbed low output 454's I don't think liked to turn many rpm's(4400 IIRC is about it for them). Propping is a science, pitch is just a number, you need to also know gear ratio to figure prop slip. The last boat I propped was a 26' SeaRay, we went from 21p 3 blade stainless props to 18p 4 blade stainless props, and gained speed everywhere, greatly improved the holeshot, improved economy, and actually reduced cruise & wot rpm's by bringing his prop slip way down and getting props that would lift the bow up.
this is a mpi 454 310 or 330 hp output boat. I dont know what leg means? it rides great. You do have to trim it up quite a bit, but i thought in theory you should have to do that. the gear ratio is 1.5 bravo one.
 

Yngdmax92

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Sep 26, 2013
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You can go down in diameter and up in pitch and still have same load the slip will just go up. Like Ferm said it is a science, I use The Prop God a good bit. He has setup more boats than anyone except Reggie Fountain, and if you can't figure it out Reggies original offshore powerboat riggor lives in Wilmington and owns Marker 17 marine, Brian knows his shit...
so your saying i should look for a 13 ish inch prop with a 21 p and see what that result gives me?
 

NC-smokinlmm

<<<Future tuna killer
May 29, 2011
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13.5" should give you a tad more rpm and pick up what your looking for but it wouldn't hurt to try the 13 if your turning a 14 now.
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
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I'm with Ferm. Small port 454 won't turn very many rpm (and still make power), I'd leave the prop alone and find some hp
 

Yngdmax92

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Sep 26, 2013
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I'm with Ferm. Small port 454 won't turn very many rpm (and still make power), I'd leave the prop alone and find some hp
Precisely what I would like to do, but.... I know marine engines are a different story when building them. I need to pick someone's brain that knows a thing or two about marine hp builds. Does anyone know of anybody I should talk to, that will sell a kit, or take my block and make it have more hp. Something along those lines.
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
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Need to find out what kind of ccp it has. No need for a full build unless it's wore out, good top end on a stock short block 454 will be fine in a boat. Do you know what the rpm and HP rating the outdrive has?
 

Yngdmax92

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Sep 26, 2013
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the bravo one is the one to have and not worry about when making power. its not about how much it will take but how you give it the power. i know plenty of people that have 500-600 hp on a bravo one. take off nice and easy and get the boat on plane and just slowly ease into it and it will live. if you are giving it wot on a stand still, i have been told the out drive will be on someone's bench more then on the boat.
 

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