carb help

[greenwell001]

hey guys, i read in a prior post about a edlbrock (650cfm) that could maybe replace to two barrel that i have on my 1996 5.7L merc. Is this a regular carb or a marine carb and will it help performance or is it just a straight swap?
any help would be appreciated. also could i put non marine heads on my 5.7?

 

[rs2k]

Re: carb help

A head is a head when it comes to the 5.7. You can put on whatever head you wish. There was a change to the heads in 1987 though. The intake manifold bolts are vertical instead of angled after 1986. To go from a 2 bbl to a 4 bbl will probably require a new intake manifold which are available all over the place. Try to get a square bore manifold if you can.

What number is on the Edelbrock? They made several different 650 CFM carbs. The 1409 and 1410 are popular Edelbrock marine carbs.

If you need to change the heads AND intake then now is a perfect time to upgrade to Vortec heads.

 

[greenwell001]

Re: carb help

thanks rs2k. i have some Ls1 heads of a 97 corvette. which one of the edlbrock carbs would you recomend for my application. Will i need to change the cam since everything is rollerized on the heads?

 

[bruceb58]

Re: carb help

Is this an aluminum head? If so, don't want to use it unless you go closed cooling.

 

[rs2k]

Re: carb help

Oh, that's a bit of a problem. The LS1 is an incredible motor, but it isn't really a 350. The parts from an LS1 will not fit on an LT1 or the earlier SBCs. Anyway, you'll want to stay away from aluminum heads and blocks in a boat. They do not like to be raw water cooled. If your boat had a closed cooling system then you could use aluminum parts, but you can still have issues.

 

[greenwell001]

Re: carb help

i can learn alot from you guys thanks again. i think i am pushing the rated 260hp. The reason for the questions is i would like to get to 300hp. do you guys have any recomendation on head/intake/carb? I would love to cam it but dont know what i would be getting myself into pulling the motor

 

[rs2k]

Re: carb help

Maybe someone else can chime in on this, but I have been told that a 260HP non Vortec marine 350 should put out 300 HP when changed over to Vortec heads.

260 HP is a lot of power for a 2 barrel carb. Are you sure it's a 260 HP?

 

[greenwell001]

Re: carb help

I kinda thought that too? I havent took the cover off of the carb but i looked underneath the best i could and it looked like a two barrel to me. As far as the hp goes, i can keep up with and sometime out run my brothers 21' baja with multi port 5.7. Our boats are identicle in size. That makes me wonder but on mercruiser website i believe that that is all the 5.7's came out with back then, unless it was the mag

 

[rs2k]

Re: carb help

A 1996 merc 5.7 with only a 2 BBL carb does not sound right to me. A marine 5.7 should have no trouble pumping over 400 CFM and most 2 BBL carbs don't flow over 400 CFM (I guess it could possibly be a 500 CFM carb). 1996 was also the first year for Vortec, but that doesn't mean you have a Vortec engine.

Are you sure you don't have fuel injection? A TBI fuel injection throttle body unit can be confused with a 2 BBL carb.

Why are you wanting to do this work to your boat? It sounds to me like it's running good as is right now. You know the two old saying:
If it ain't broke, don't fix it
-and-
KISS (Keep it Simple Stupid)

 

[greenwell001]

Re: carb help

alright guys, it is definately a 2 barrel. i dont see how it is pushing my boat this good but it hauls a**. how hard is it to switch over to tbi?

 

[Bigdave196]

Re: carb help

WAIT....STOP....hold on for a second.

Depending on your boat manufacturer and the available options you had for your boat, you might not be wired in for TPI/MFI/TBI. Stand alone kits for the wiring harnesses go for around $1200 and then you need to get a higher pressure fuel pump/electrical pump, and the TBI unit itself. Its not really worth it unless your boat was pre-wired and you can find good parts.

I have your similar motor. I have a 96 Blue Water-open bow 22' ski boat, 5.7L, Alpha 1 Gen II, 19* SS prop, 1.50 gears.

My boat has the 600CFM Edelbrock marine 4BBL carb no choke. I rebuilt my motor this last winter and Loved the performance difference once it was properly dialed in.

If your looking to make the 260HP into a 300 HP set up here are a few things I would reccomend the following,

*Vortec Steel heads $300-$500 for the pair
*Performance intake manifold compatable to your carb of chioce $200
*Upgrade the plugs and wires and coil. ( I assume you have the ThunderBolt IV or ThunderBolt V.) Parts are made available for both $100-$300 depending on your desires and wallet.

This all can be purchased at most normal engine reman/rebuild shops or machine shops without having to buy new. Your Carb needs to be a "Marine Grade" carb for Safety reasons. Those run about $350, look around on the internet, FYI--JEGS and PAW want over $1000 for the same carbs.

Do not buy Aluminum heads or intake manifolds unless they are marine grade and you can see the lining inside. This causes some kind of magnitizing of the water and does weird crap to your motor. Dont know what or why but its a common known issue, and best to stay away.

 

[John_S]

Re: carb help

A stock '96 2brl 5.7L Mercruiser would be 210HP, not 260HP. They have standard heads, not vortec. In '96, Merc started using vortec heads with some models and called them gen+. A 2brl carbed vortec didn't show up until '98, and it was rated at 250HP.

Changing your 5.7L to vortec heads and 4brl / intake will get you to 280HP at prop. To reach 300HP with bolt-ons, a mild cam increase is needed.

All ratings are Mercs @ prop.

 

[mkast]

Re: carb help

Do not buy Aluminum heads or intake manifolds unless they are marine grade and you can see the lining inside. This causes some kind of magnitizing of the water and does weird crap to your motor. Dont know what or why but its a common known issue, and best to stay away.

For a commonly known issue, I've never heard of it.
Care to elaborate?

 

[Bigdave196]

Re: carb help

I was told by several MERC certified mechanics that if you put Aluminum heads on the Steel block marine applications that it tends to magnetically charge the parts of the block. You need to have (copper) lined water ports to keep this from happening and messing up parts of the motor.
The only reason I heard about this is because I was thinking of swapping out my Cast Iron heads for an Alum heads/intake set up for the extra HP and to be a little lighter in the back of the boat.

Several mechanics (from different places) said the same thing, so I took it as fact. Since they are the people who get paid to guild and maintain these motors I want going to argue.

 

[greenwell001]

Re: carb help

thanks for all the input, how could i find out if it is a 98 w/ vortec, it can run with my brothers baja and he has the mpi w/ vortec heads. maybe i am wrong about the year. just doesnt seem like it only has 210hp

 

[Bt Doctur]

Re: carb help

OK, lets reverse that. The 3.7 uses a aluminum block with a cast 460 truck head. No such issues

 

[mkast]

Re: carb help

You need to have (copper) lined water ports to keep this from happening and messing up parts of the motor.

Several mechanics (from different places) said the same thing, so I took it as fact. Since they are the people who get paid to guild and maintain these motors I want going to argue.

The inserts in the marine intake manifold are brass not copper.
Did these mechanics tell you the inserts were copper?
To magnetize water, a magnet has to be present, for a considerable amount of time. Where on the engine is the magnet? The cooling water doesn't hang around, it's dumped overboard.
Tell me you're not one of these guys with magnets on the fuel line.

 

[greenwell001]

Re: carb help

big dave,

i dont know alot about boat motors but i do know alot about metals. There are alot of way steel can be magnetized, aluminum can not be magnetized no matter what you do to it. Steel can be magnetized in the machining process, if current is ran through it, even certain chemicals can magnetize steel. I work at a hard chrome, metal conditioning facility so i pretty knowledgeable about this. I cant see water magnetizing anything, but if you heat it up and cool it down very fast and numerous times it can be magnetic, aluminum and steel conduct heat at very different paces and cool of at very different paces and this could be why it becomes magnetic, or maybe it has to do with saltwater, anyway i wanted some carb help that is the reason i started the thread can you help me with that?

 

[mkast]

Re: carb help

Replace your two barrel with ANY four barrel MARINE carb that fits the manifold you are getting.

 

[rs2k]

Re: carb help

The reason you can't use aluminum is because it reacts with the salt water and causes corrosion much quicker than when using iron. You can get by with using aluminum in fresh water, but it is still not recommended. If you use aluminum parts in salt water you need a closed cooling system. It's a type of electrolysis corrosion I believe. It's a similar action that corrodes zinc anodes. Technically, you can consider electrolysis a magnetic phenomenon because it is electro-magnetic in nature, but for all intents and purposes it is not a magnetic problem.


Vortec heads and a 4 bbl carb will really increase the performance on that engine.