2 bbl vs 4 bbl carb

df909

Petty Officer 1st Class
Joined
Nov 28, 2009
Messages
333
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.
 

Bondo

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Staff member
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Apr 17, 2002
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70,465
Re: 2 bbl vs 4 bbl carb

Ayuh,.... about 20hp....
 

zbnutcase

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Sep 19, 2009
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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
 

180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
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.
 

havasuboatman

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Mar 5, 2009
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904
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.
 

Bondo

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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...
 

mkast

Lieutenant Commander
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Nov 6, 2002
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Re: 2 bbl vs 4 bbl carb

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.
 

havasuboatman

Ensign
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Mar 5, 2009
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904
Re: 2 bbl vs 4 bbl carb

C'mon Bond-o, comparing inboards to out boards is like comparing apples to door panels.
 

180shabah

Rear Admiral
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Mar 26, 2005
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4,995
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.
 

Bondo

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Staff member
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Re: 2 bbl vs 4 bbl carb

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...
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
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
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
Re: 2 bbl vs 4 bbl carb

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.
 

180shabah

Rear Admiral
Joined
Mar 26, 2005
Messages
4,995
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.
 

mkast

Lieutenant Commander
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Nov 6, 2002
Messages
1,934
Re: 2 bbl vs 4 bbl carb

Marine aluminum intake manifolds use brass inserts lining the coolant passages.
 
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