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  1. #1
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    Default 2 bbl vs 4 bbl carb

    Hey Guys-

    I have a 1992 4.3L with an Alpha 1 drive. It has a 2 bbl carb now and I'm going to replace the intake manifold and put in a 4 bbl. How much do you think I'll notice a difference on hole shot, top end, and fuel consumption?

    In case it matters, I run a 4-blade 19p aluminum prop and at WOT hit about 4600 RPM with two adults and two kids and can just reach 45 mph.

    Do you think I'll have to increase the pitch on the prop to avoid over-reving? If I do up the pitch, I imagine I'll lose some hole shot, right?

    Thanks.
    Spicoli for president - Mr. Hand for V-P

  2. #2
    Moderator Bondo's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Ayuh,.... about 20hp....
    Any Grease is Better,..... Than No Grease at All.......

  3. #3
    Commander zbnutcase's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    And use a marine carb and take the time or pay somebody knowlegable to tune it after the install. 'nutcase

  4. #4
    Rear Admiral 180shabah's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Change in holeshot will be negligable, if any. If you set it up properly, fuel consumption should be the same...IF...you control your right arm. Midrange acceleration and top speed will both improve a little.

  5. #5
    Ensign havasuboatman's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    When you look for more power by just replacing the carb, you are almost always going to be disappointed.
    Just dumping more fuel into an engine just wastes fuel.
    Your carb is matched to your cam specs; lift, duration, and overlap. You have to get that mixture into the cylinder, and just as importantly, you have to get the exhaust out.
    Don't be suprised if the biggest difference you notice is fuel economy going down, and the unpleasant smell of an engine running rich.
    Hey, it was like that when I got here.

  6. #6
    Moderator Bondo's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Your carb is matched
    I disagree,... The only difference in the Merc motors is the change in Carb, for more HP...
    Any Grease is Better,..... Than No Grease at All.......

  7. #7
    Lieutenant Commander mkast's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Quote Originally Posted by havasuboatman View Post
    Your carb is matched to your cam specs; lift, duration, and overlap.
    The example I looked up was a 1996 4.3LX.
    The part number 431-803186 camshaft, is listed as the same camshaft for both the two barrel and four barrel Mercruiser engine. You will find, as in the 350 engine, the same cam is used in either two or four barrel engines. The thought process is, the cam will handle a four barrel so what if a two barrel is installed, this way I only have to deal with one part number.
    From Mercruiser:
    Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the productís safety will be endangered by the service procedure selected.

  8. #8
    Ensign havasuboatman's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    C'mon Bond-o, comparing inboards to out boards is like comparing apples to door panels.
    Hey, it was like that when I got here.

  9. #9
    Rear Admiral 180shabah's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    How did we get on Outboards????

    A properly tuned 4bbl does not use any more fuel while cruising than a comparable 2bbl. If you can smell your engine running rich, then you need to get the tool bag back out and start over with the tuning 'cause you didn't get it right.

  10. #10
    Moderator Bondo's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Quote Originally Posted by havasuboatman View Post
    C'mon Bond-o, comparing inboards to out boards is like comparing apples to door panels.
    Ayuh,... Donno what You're talking about,.... I'm still talkin' about I/Os...
    Any Grease is Better,..... Than No Grease at All.......

  11. #11
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    Default Re: 2 bbl vs 4 bbl carb

    96 4.3L Rochester/Mercarb 2barrel

    96 4.3LX Rochester Q-jet

    Differences were intake, carb and...............


    HP decals

  12. #12
    Rear Admiral 180shabah's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    96 = weber

  13. #13
    Supreme Mariner bruceb58's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Quote Originally Posted by Bubba1235 View Post
    Edelbrock offers V6-90 Performer low-rise dual-planes PN 2111 for heads with traditional angled bolts or PN 2114 for true Vortec heads with vertical intake-manifold attaching bolts.
    Correct me if I am wrong but isn't that an aluminum manifold? Should not be used on a raw water cooled engine.
    1998 Wellcraft Eclipse 24 Cuddy
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  14. #14
    Rear Admiral 180shabah's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Yeah, aluminum is fine in a fresh water application. For that matter you could do running salt water, just consider the manifold a normal replacement item every other year. real PITA if you ask me though. Of course mine requires engine removal to get the intake manifold off.

  15. #15
    Lieutenant Commander mkast's Avatar
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    Default Re: 2 bbl vs 4 bbl carb

    Marine aluminum intake manifolds use brass inserts lining the coolant passages.
    From Mercruiser:
    Anyone who uses a service procedure and/or tool, which is not recommended by the manufacturer, first must completely satisfy himself that neither his nor the productís safety will be endangered by the service procedure selected.

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