94 7.4B Carburated
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94 7.4B Carburated

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    Senior Member Capitalgains's Avatar
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    Default 94 7.4B Carburated

    Okay guys, I purchased my first performance boat and I need some help. I have a 94 2900 Envision with a 7.4 carburated engine with a bravo 3 outdrive with only 192 total hrs on the boat and motor. I know It is lacking power and the brovo three is not a high power outdrive. I am looking for advice or a good plan to make more power. I am only running around 50 mph at top speed. The prop is a 26P. I am not a baller so switching out to a 525 or ilmor is out of the question. Where do you start? Intake and carb? Is there a rule of thumb one can follow.
    Last edited by Capitalgains; 09-29-2010 at 06:44 PM.

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    Senior Member alkyexpress's Avatar
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    I would check on how much the Bravo-3 drive will take first (safely), (I think this is in Big Steve's territory ) then do some motor work to fit that , jmo . ...E

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    deckboat owner rschap1's Avatar
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    BIII is just about like a Bravo as far as what it will handle.
    If not abused I wouldn't sweat the outdrive.
    You will be able to agin a few mphs top end with a single prop Bravo, but the twin counter rotation B3s launch and do better in mid-range. You will loose the "traction" you have now. I enjoyed my B3 on a 237 Powerquest.
    Maybe cam, roller rockers and tune for your motor. Much more than that and the bottom end will show as weak link and you'll atleast want forged Magnum motor components. You could probably get 400 horse or so from that motor and will be ready to change prop set. 60s-mid 60s. Then you will be looking at bigger $$
    Good Luck!

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    Senior Member Capitalgains's Avatar
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    It sounds like the B3 can handle the power. Cam and roller rockers sounds like a good place to start. I am pretty new at this but how do you know what to buy? I would happy with 60-65. I am not looking to set speed records. Just dont want to be left behind. I was looking at intake, carb and ingition replacement to start but wanted other opinions. Thanks for the info.

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    A 10 to 15 mph increase is going to take more then cam and intake. Lets start with the most important: What is the budget? You can do small upgrades that will help in the future now if the budget is not quite there yet.
    Chris Straub
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    Purple headed member Quickjet's Avatar
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    Cam, Rockers, carb and a Procharger.
    Done!!
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    Keith...
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    deckboat owner rschap1's Avatar
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    Default oops

    I guess I was assuming better than flat 50 mph as it stands. No I would not guess 10-15 increase that easy either. I had always schemed to do the motor in my PowerQuest but never did. So no real world results, sorry. I had always guessed that the 1995 7.4 carb motor I had would have approached 400 hp had I stuck in the right cam, lifters, rockers, carb, and intake. I figured after that I would have needed exhaust ($$) and probably blown the bottom end apart or started showing a need for new heads beyond that point. My boat had done just shy of 60 just about any time, it bumped the rev limiter once and saw 62. I was thinking more of what I had experience in just a little bigger boat. But I guess a 29 footer compared to my 237, and 50 stock compared to near 60 is a lot further to stretch.

    Now I putt around in my v-6 volvo powered deckboat anyways
    Last edited by rschap1; 09-30-2010 at 10:33 AM.

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    Senior Member Capitalgains's Avatar
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    This motor is completly stock and looks brand new. I am on a three year plan to payoff and resale to move up to what I really want. It is very reliable but I would like more speed. What kind of gain would you see with just a intake and carb. Is there a happy meduim or can I get there for around 3K?

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    Senior Member Capitalgains's Avatar
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    Quote Originally Posted by cstraub View Post
    A 10 to 15 mph increase is going to take more then cam and intake. Lets start with the most important: What is the budget? You can do small upgrades that will help in the future now if the budget is not quite there yet.
    I like the small upgrade scenerio. I dont whant to go overboard because I will be selling later. Where do you start on the small upgrades?

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    It's what we do BDMarine's Avatar
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    Quote Originally Posted by cstraub View Post
    A 10 to 15 mph increase is going to take more then cam and intake. Lets start with the most important: What is the budget? You can do small upgrades that will help in the future now if the budget is not quite there yet.
    X2.... Not going to see a 10 to 15 mph gain.

    That engine will respond decently to exhaust upgrades. The first place to start is with exhaust. Then move to cam, etc. You need to understand that engine is a MPI and you will have to find someone GOOD at tuning MEFI IV ECU's if you do anything other than exhaust.
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    Senior Member Capitalgains's Avatar
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    MPI (multiport injection)? It is a carb motor at about 330 hp. But is the exhaust the right place to start? Thanks for the input. I found i can purchase a new 415hp long block for around 6800 from one of the sponsers. But I would rather start with small upgrades.

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    Quote Originally Posted by Capitalgains View Post
    MPI (multiport injection)? It is a carb motor at about 330 hp. But is the exhaust the right place to start? Thanks for the input. I found i can purchase a new 415hp long block for around 6800 from one of the sponsers. But I would rather start with small upgrades.
    I had the same engine in a '97 Rinker Captiva. I put the GLM aluminum Exhaust and an Airgap intake on mine. No other changes and I gained at best about 150 to 200 rpm out of mine.

    Weak point on these engines are the heads. They have bolt down rockers and other items that not conducent to "upgrades". Now to bolt a set of aluminum Ebrock ovals on what you have along with intake and exhaust, and a camshaft for now you may see 6 to 8mph out of those changes. These would all be upgrades that later on could be bolted to a 496 using your block as "homebase" or a short block 502.
    Chris Straub
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    gn7
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    Quote Originally Posted by BDMarine View Post
    X2.. You need to understand that engine is a MPI and you will have to find someone GOOD at tuning MEFI IV ECU's if you do anything other than exhaust.
    OK, its time to put down the Capt'n Morgans, put out the stogey and sit up straight and pay attention. It carb motor.



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  16. #14
    cfm
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    Since I do not know these boats at all, and since a 29ft boat with a low hp motor makes no performance sense, I did some quick searching for info on them to try to get a feel for what speeds they'll run with more power.

    I ran into the report below right off the bat.

    Looks like you'll need a bunch more hp that just bolt on stuff to get you to the 60mph mark.

    Link here:
    http://features.boats.com/boat-conte...900-combo-dlx/

    Partial quote below:

    For power we had a 375 hp 496 MAG MerCruiser with a Bravo I drive spinning a 21-inch Mirage Plus three-blade stainless steel prop. On the dash we had Livorsi gauges, and to our right we had Kiekhafer throttle controls. Even before putting the beast in gear we knew we were in for a treat.

    The 2900 powered out of the hole with good speed for an on-plane time of 4.9 seconds and a 0- to 30-mph time of 9.5 seconds. With the throttle mashed all the way forward and the drive trimmed up for speed, we posted 53.1 mph on our GPS with 91 dBa for sound.
    Last edited by cfm; 09-30-2010 at 03:18 PM. Reason: I said 600mph - LOL

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