Merc 7.4 MPI build suggestions?
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Merc 7.4 MPI build suggestions?

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    Senior Member PuraVida Victory's Avatar
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    Default Merc 7.4 MPI build suggestions?

    Hey guys im looking into rebuilding the motor in my boat. Its a 1998 Advantage 27'Victory with a Mercruiser 7.4L MPI. I still dont know the direction i want to go with it yet. all i know is if i can get to that 85MPH mark i'd be happy. I would like to do it without forced induction but like i said im not sure yet. im not looking to make an all out race motor, just something reliable that if i wanted to i can add more power to later on down the road.I know there is not much as far as a multi port set up so if i have to change it its not that big of a deal and i figured its basically a 454 so it shouldnt be to hard. the outdrive is the original bravo 1 so and im not sure how much power they can handle. Any advice on a good direction would be awesome. Thanks

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    Quote Originally Posted by PuraVida Victory View Post
    Hey guys im looking into rebuilding the motor in my boat. Its a 1998 Advantage 27'Victory with a Mercruiser 7.4L MPI. I still dont know the direction i want to go with it yet. all i know is if i can get to that 85MPH mark i'd be happy. I would like to do it without forced induction but like i said im not sure yet. im not looking to make an all out race motor, just something reliable that if i wanted to i can add more power to later on down the road.I know there is not much as far as a multi port set up so if i have to change it its not that big of a deal and i figured its basically a 454 so it shouldnt be to hard. the outdrive is the original bravo 1 so and im not sure how much power they can handle. Any advice on a good direction would be awesome. Thanks
    First you need to consider what your budget is, and how much horsepower it takes to make that particular boat go 85 MPH, and see what you can do. The Bravo 1 is supposed to be good for 600 HP I believe, and you need to build an engine that will idle down to 800 RPM to get the drive in and out of gear without tearing it apart.

    If 600 HP will get you to your desired speed, easiest way to do it may be a stroker 496?

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    New here Beer:30's Avatar
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    If you want a "kit" that will provide another 100hp, another guy here "kevnmcd" did this setup years ago. Works like it should: Crockett Marine Engines
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by obnoxious001 View Post
    First you need to consider what your budget is, and how much horsepower it takes to make that particular boat go 85 MPH, and see what you can do. The Bravo 1 is supposed to be good for 600 HP I believe, and you need to build an engine that will idle down to 800 RPM to get the drive in and out of gear without tearing it apart.

    If 600 HP will get you to your desired speed, easiest way to do it may be a stroker 496?
    I just dont want to spend a boat load trying to make a race motor, id like to keep it under 3-4k. Now i know if im buying heads, pistons, rods, and doing machining it can add up quick but i plan on doing most if not all of the assembly myself. As far as horse power, im not sure how much i would need to get the boat to do 85. I do know that my setup right now probably puts out around 320hp. 600 would be a massive improvement. I do know that i have seen the same boat with a Merc racing 525 do about 80, and i have a cousin with twin stock 496s in a 30 victory that will do almost 90 on glass. I dont know about some choppy stuff. So i know the boat can handle the speed. it is pretty heavy though, around 4600 pounds with no one or crap in it. 100 gallons of fuel+5 people+all kinds of S***, it gets up there. If im lucky I can break 50 right now with the hammer all the way down.

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    New here Beer:30's Avatar
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    I'm around 6000 pounds - on the water, with probably around 435-440hp. I swing a stock 24p B1 prop just to touching the rev-limiter (5150 rpm). That said, when it's up on the back step and aired out with 4 adults, half-fuel or so, two ice chests (1/2 empty too), I'll hit 64-65 on a moderately warm day.

    As I recall, the 27 Victory is a single-step hull? That'll definitely help you with a bit more hp. Getting that boat OUT of the water is what you are needing your HP for.

    Being as how you will "do it yourself", I really suggest a kit that is PROVEN to work. Edelbrock has a nice "top end" package of heads, cam, intake, etc., all as a kit.

    Same with the Crockett package. KEVNMCD on here did a play by play picture show of the build using his old motor and dialing-in the Crockett kit. He was severely happy with the results. As I recall, he even used a BACKHOE to R&R the engine!

    I believe that was on the old HOTBOAT forums. I'll see if there is anything on here.

    Being a DIY'er, you really need to use a kit that will remove all of the guesswork. IMO.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Quote Originally Posted by Beer:30 View Post
    I'm around 6000 pounds - on the water, with probably around 435-440hp. I swing a stock 24p B1 prop just to touching the rev-limiter (5150 rpm). That said, when it's up on the back step and aired out with 4 adults, half-fuel or so, two ice chests (1/2 empty too), I'll hit 64-65 on a moderately warm day.

    As I recall, the 27 Victory is a single-step hull? That'll definitely help you with a bit more hp. Getting that boat OUT of the water is what you are needing your HP for.

    Being as how you will "do it yourself", I really suggest a kit that is PROVEN to work. Edelbrock has a nice "top end" package of heads, cam, intake, etc., all as a kit.

    Same with the Crockett package. KEVNMCD on here did a play by play picture show of the build using his old motor and dialing-in the Crockett kit. He was severely happy with the results. As I recall, he even used a BACKHOE to R&R the engine!

    I believe that was on the old HOTBOAT forums. I'll see if there is anything on here.

    Being a DIY'er, you really need to use a kit that will remove all of the guesswork. IMO.
    That makes alot of sense. A kit definitely would make it a lot easier. Would that kit ditch the multi port set up for carb? That crockett kit seemed pretty good but it didnt give a price on the site, do you know how much it was?
    I would be doing almost all the assembly my self, but if i need any machining, boreing, decking etc. i would have a shop do it because i just dont have the machinery for it.

    The boat is a single step. How does that help me though? I would have figured that more steps would be better,then again i dont know to much in this area.

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    Quote Originally Posted by PuraVida Victory View Post
    Hey guys im looking into rebuilding the motor in my boat. Its a 1998 Advantage 27'Victory with a Mercruiser 7.4L MPI. I still dont know the direction i want to go with it yet. all i know is if i can get to that 85MPH mark i'd be happy. I would like to do it without forced induction but like i said im not sure yet. im not looking to make an all out race motor, just something reliable that if i wanted to i can add more power to later on down the road.I know there is not much as far as a multi port set up so if i have to change it its not that big of a deal and i figured its basically a 454 so it shouldnt be to hard. the outdrive is the original bravo 1 so and im not sure how much power they can handle. Any advice on a good direction would be awesome. Thanks
    I think your being pretty optimistic with wanting 85 out of a massaged 454. It's surprising how much HP it takes to gain 10mph, especially in a Vee. Also consider that your B1 won't be happy very long with the added power in such a heavy boat. What speed (gps), rpm and prop do you have now?

    We ran a 572 w a BS 250 in a pretty light 23' tunnel for a long time w/o any problems, but it did fail eventually. I don't have any experience w the 27 Vic, but a Hallett 270 w an HP500 will run high 60s to low 70s with a straight bottom. A bit better w a single step.

    I have a 97 270 straight bottom open bow that weighs in around 4200 plus 125g fuel. We are still playing w the setup, but, with a 580 quad rotor, we are right around 85 at 5300rpm 30" 5 blade prop and 6-7psi.

    Good luck w the build. Keep us updated.

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    Quote Originally Posted by PuraVida Victory View Post
    A kit definitely would make it a lot easier. Would that kit ditch the multi port set up for carb?

    The boat is a single step. How does that help me though? I would have figured that more steps would be better,then again i dont know to much in this area.
    1) Absolutely NOT. Tyler Crockett would NEVER go backwards to a carb.....if you read, part of the kit is reprogramming YOUR ecm.

    2) Of course, more steps, more speed - but I was just making sure you at least HAD a stepped hull. All a step does is make the boat act like a BIG boat when OFF of the step and a LITTLE boat when ON the step. Lots of hull in the water - it acts like a 27 footer. Up on the step - it acts like, say, a 24. More speed.
    Quote Originally Posted by gn7 View Post
    EFI is the wave of the future. There can be no denying it. Electronics have been on the leading edge of our entire lives. Not only os the magneto dead, but the standard issue CDI is wavering. Its all about total fuel, air AND spark control. Anybody that thinks its not has their head up their ass.


    2001 SleekCraft 30' Heritage SSB, open-bow mid-cuddy. 496HO / Bravo-I.

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    Im Not saying i want 85 out of it im just saying if it will go that fast that would be awesome. At this point any speed increase would be great. Im just tired of getting past by every other boat on the water. Not only that it takes about a million years to get it to plane out.
    Right now im running a 3 blade mirage i think its a 27p or 29p. Im not sure. Basically on a good day if i can get to 50 its over 5000rpm.
    Now i dont plan on leaving it like this forever. I do want to add a turbo kit or supercharger down the road, but way down the road. right now i just want to try and get as much as i can without spending a fortune and not have to do anything serious with the outdrive.

    Beer:30 I was actually talking about that edlebrock kit you mentioned. The crockett kit looks pretty nice though.

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    Quote Originally Posted by PuraVida Victory View Post
    Im Not saying i want 85 out of it im just saying if it will go that fast that would be awesome. At this point any speed increase would be great. Im just tired of getting past by every other boat on the water. Not only that it takes about a million years to get it to plane out.
    Right now im running a 3 blade mirage i think its a 27p or 29p. Im not sure. Basically on a good day if i can get to 50 its over 5000rpm.
    Now i dont plan on leaving it like this forever. I do want to add a turbo kit or supercharger down the road, but way down the road. right now i just want to try and get as much as i can without spending a fortune and not have to do anything serious with the outdrive.

    Beer:30 I was actually talking about that edlebrock kit you mentioned. The crockett kit looks pretty nice though.
    I'd try to borrow a bravo 1 or 5 blade (px5 worked good for me) in a 24-26 for sure. That will help to plain quicker and should also help up top. The 3 blade has a ton of slip. When I tested a bravo 1 and a px5, I gained about 5mph at cruise, and maybe a bit more on top.

    I finally went w a cutting edge 5 blade that actually got me a bit more than the px5.


    Sent from my iPhone using Tapatalk

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    I have a bravoI 30p i got for free from someone, how would that do do you think. I havent been able to try it out yet.

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    Quote Originally Posted by PuraVida Victory View Post
    I have a bravoI 30p i got for free from someone, how would that do do you think. I havent been able to try it out yet.
    That's a pretty big prop, but try it. It'll probably be slower w less rpm. Remember-more blades, more bite' which will drop your rpm if it's too big. The rule of thumb is to drop a size when you go from 3-4 and 4-5. That's why I was suggested trying a 24 or 26. I think you'll be happiest w a five blade though. Sometimes you can get a shop to let you test 2 or 3 props if you leave a deposit.

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    Our neighbor in Bullhead has a hole garage full of props, im sure i can borrow one. Thanks for the tip though. we have never tried another prop on the boat.

    As far as the motor goes, i probably wolnt start this project for at least a year. Need to save some benjamins. Im just looking for a general direction and what to expect. But all the advice is greatly appreciated guys.

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    Quote Originally Posted by PuraVida Victory View Post
    Our neighbor in Bullhead has a hole garage full of props, im sure i can borrow one. Thanks for the tip though. we have never tried another prop on the boat.

    As far as the motor goes, i probably wolnt start this project for at least a year. Need to save some benjamins. Im just looking for a general direction and what to expect. But all the advice is greatly appreciated guys.
    Definitely try props. That will be a good start, then watch the classified for take outs. That way you can sell yours and recoup a bit. We'll be in Havi and Mead over the summer, so I'll keep an eye out for ya.

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