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97 Maxum 5.7L mercruiser engine 2 barrel to 4 barrel question

gica69

Regular Contributor
Is there a huge advantage and what does it involve. Do I need to replace the intake are there adapter plates?
Can a more performant Holley 500cfm carb get the same performance?
Can anyone suggest a decent not s expensive deal?
Thanks in advance
 
You will need a intake manifold for a 4 barrel . Inspect the 4 bolts under the carb, are they angled or straight, it makes a difference
 
They make adapters to mount a 4 BBL carb on a 2 BBL intake...if you have the vertical clearance, that's one path.

As suggested by BT, your best 'performance' will come from a 4 BBL intake with a matching carb base.

There isn't much 'performance gain' switching to the 4 BBL, unless you run at close to WOT (secondaries active)...and then it won't be a huge gain.

Unfortunately, there isn't anything 'new' that's inexpensive anymore...
 
Ok do forget about the 4bbl. I now have 2bbl and was gonna rebuild but removed the throttle plates bolts and broke one. Cannot find a shaft by itself.1_So I think I better get a new carb. Someone mentioned the Holley 2300 2bbl avenger with rochester to Holley adapter plate. Any ideas?
 
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bolt on??? with the correct adapter...

Looked closely at that link and followed the main menu to the MARINE systems.

They offer a Quadrajet manifold specific Marine system is 600 cfm and 750 cfm

1. Need O2 port for sensor. (most difficult issue to overcome in a marine environment and images in system PDF shows auto exhaust) Usually what is needed is an exhaust elbow modification or add a spacer (riser) between manifold and elbow modified for O2 Bung
2. Need return line to tank (they show a specific type of return line configuration inside tank) not sure that is 100% required as shown....
3. Need regulator for return line to tank.
4. Need 58 psi fuel pump plus pre pump and post pump inline filters.
5. Need a lot of confidence to do this right on a boat! Not for the typical back yard Ricardo type......

If Holley offered a more plug and play system with all parts needed in one kit then only a couple of the list above would need consideration.
 
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Agreed and if you read the questions posted on the Holley support forums, you can see that these systems are not just plug and play as people might think. You're adding a lot of complexity with new possible problems to pop up just take a good look at the wiring harness you have to add (youtube some installs on classic cars). Yes EFI will run consistently better cold starts and cold running, but if you have a well set up and CLEAN carb you have a system far simpler to maintain IMO, and it will run good enough, for most people. Adding a 4bbl carb is going to add more response above 3500 rpms when the secondaries open up. Is it worth it? That depends on you. I think it is but to each their own. To make it work, you have to replace the 2bbl manifold with a 4bbl manifold, of course a new 4bbl carb, and there may be changes needed to the fuel line and accel linkage. On a Merc to make it easier you can use an Edelbrock carb because they came with Webers after the Q-Jet stopped production and the Weber is similar to the Edelbrock so the OEM linkages would most likely work, as might the fuel lines.
I have a Q-Jet on my little 4.3 and am addicted to the Q-Jet howl as the secondaries open up, so for me yes 4bbl all the way....
 
Actually the EFI is simpler. Has one moving part (throttle butterfly) and once it's set, there's nothing else needed. You have to tune a carb too, no? Marine EFI doesn't require oxy sensor.
Does need a bit of plumbing tho for return line.
 
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