Merc 2bbl to 4bbl conversion

[95yj]

Kicking around possibly swapping out the stock Merc 2bbl with a 4bbl on my '97 (non vortec) 5.7L Merc. I've seen a lot of folks here stating that the E-1409 carb from Edelbrock works well for this application. Since I have closed cooling, I was also going to replace the cast iron manifold with an aluminum. Couple questions for anyone who's done this swap.

Edelbrock's site states the Performer RPM manifold won't work with cast iron BT heads after '87. What's the best manifold for this ap?

Any issues with mounting the old bracket that holds the throttle linkage, main fuse and slave solenoid to the new carb? What changes need, if any, to be made to the throttle linkage to mount to the new carb?

 

[Mkos1980]

Re: Merc 2bbl to 4bbl conversion

You need the Mercruisers (GM) HighRise 4bbl intake manifold. Its identical to the Edelbrock RPM series but is cast iron and fits 87 and up heads. It is the intake that the Magnum motors use. I recently swapped out my low rise 4bbl to the highrise 4bbl and gained 2 mph. I used my origional Q jet. All linkage fit perfect and everything. Even the fuel line with a tad of tweakness. Only thing I didnt get was a new divorsed choke rod. I eliminated my choke all together. Starts fine still. Better then when I had choke. I removed my choke plate from the carb as well.

 

[wca_tim]

Re: Merc 2bbl to 4bbl conversion

I got a sense that the performer rpm wouldn't work with yours cause ya got the bowtie heads...

I tool a look on the edelborck web site, doesn't one of the ergular performer series fit it? and also isn't the performer better rpm range for marine app? would think the performer rpm is matched to a little higher rpm power band than the performer and would either be a little mismatch for the factory cam, kill some of the power off idle, or both... just thoughts. and I don't see why you would want to go with cast if you're running closed cooling. I've hd good luck with the edelbrock marine carb I'm using now...

Cheers! Tim

 

[Bondo]

Re: Merc 2bbl to 4bbl conversion

and also isn't the performer better rpm range for marine app? would think the performer rpm is matched to a little higher rpm power band than the performer and would either be a little mismatch for the factory cam, kill some of the power off idle, or both... just thoughts. and I don't see why you would want to go with cast if you're running closed cooling.

Ayuh,.......... Me Too.......

 

[95yj]

Re: Merc 2bbl to 4bbl conversion

Absolutely correct on using the Performer EPS over the RPM. I did a Google search instead of plowing around on Edelbrock's web site and only saw the RPM. The EPS is tuned to where we need the torque in a marine application. As far as using a cast iron, that just doesn't seem logical since I have closed cooling and won't have the interior corrosion/galvanic issues unless that manifold is just tuned better to what the motor is doing.

It was stated above that the 4bbl to 4bbl swap worked fine, but I'm doing a 2bbl to 4bbl swap. Does anyone know if I'll have issues mounting the rear linkage/ electrical bracket onto the new 4bbl installation? What about the throttle linkage to the carb?

Also, the Edelbrock site doesn't specifically state that the EPS won't fit on the 87 and newer heads like it does with the RPM, but it still states that the EPS is for 86 and older. What's the difference between the 86 heads and the 87 and up?

My issues are that I don't have a hardware store or auto parts store to walk into to attempt to fabricate anything, so if I order the parts, I need to get everything I need ahead of time otherwise the boat gets to sit in the front yard for another month while I track down and get a widget shipped here to the island. (Boat just looks a whole lot better sitting in the water than it does in my front yard.)

 

[Mkos1980]

Re: Merc 2bbl to 4bbl conversion

The differance in the heads is the center intake bolts. The only reason I put the Cast iron Highrise is that its the same height and runner length as the Performer RPM. Apparently Mercrusier had to do some homework with this. + You can find them on ebay for under 100. The ONLY non Airgap intake that will fit from edelbrock is the 2104

 

[Mkos1980]

Re: Merc 2bbl to 4bbl conversion

Heres a good post for you http://www.speedwake.com/upload/showthread.php?s=&threadid=49702&highlight=performer+bowtie

 

[John_S]

Re: Merc 2bbl to 4bbl conversion

I did a similiar conversion on my '97, but ended up going with vortec heads, along with the 4brl.

-You need the 4barrel carb throttle bracket. I think they are around $40, or half that on ebay. The circuit breaker bracket will bolt to this. You probably could fabricate something from the 2brl bracket, instead.

-Throttle cable attachment to carb should be fine. I went with a q-jet w/no problems.

-Your 2brl should have elec choke, so no issues with going to a Edelbrock 1409 which has same.

-You will need to fabricate a new fuel line. If you have a mech fuel pump, Merc made a fuel line for Edelbrock/weber carbs. Again, ebay is your friend.

-You need a new flame arrestor to fit the 4brl. K&N is good to go with, but the vent hose attachments are a little pricy. I was able to mount the black merc cover over the top of the K&N to give it the stock look.

-The merc thermo housing need to use the specific gasket that has contact points to provide a ground path for the two sensors.

-I primed the manifold with zinc chromate and painted it with merc phantom black. Mark, or remove the U shaped bracket ontop of the thermo housing. It is for lifting the engine out, and alum threads are not as strong as the cast ones.

If you have stock heads, they should not be Bow tie heads. Please clarify which heads you have.

I'll try to find a couple of pics to post this evening.

 

[95yj]

Re: Merc 2bbl to 4bbl conversion

Thanks for the link MKOS, some good info there on intakes. The Brodix HV1016 sounds good in the posts for their application, but the RPM range seems a little high for me. It's listed at 3000-6500 while I have a WOT of 4600 and spend a lot of time cruising comfortably at 3000. It looks like the only Edelbrock manifold that will fit is the stock 2104 performer.

JohnS, I have the stock heads that came with my OK009657 motor. And now that you mention it, I do remember reading that the center bolts are at a different angle to clear the EGR manifold and this is what my heads have. I installed an aftermarket closed cooling, so I have a different thermostat cover so that's not an issue.

I'll plow around and see if I can find the part numbers for the fuel line and the linkage/electrical bracket and then see what I can find on ebay. Same with the flame arrestor. Knew I needed a new one, but figured once I decided on the carb, I'd just order something that fit the air horn. Don't like the quadrajets. They're a lot like the thermoquads. When they're working, they work great; when you gotta dicker with them, you're in for some real headaches.

 

[John_S]

Re: Merc 2bbl to 4bbl conversion

I would go with the performer for your application. With the 2104 you can choose between a squarebore or spreadbore carb. The Edelbrock 1409 is an excellent choice, especially for ease of tuning. If you are not a q-jet fan, but still want a spreadbore, look at Holley. They have a marine 650cfm vac secondary, q-jet replacement.

Here is the part number I had in a spreadsheet:
Throttle Bracket 805359T

When looking on ebay, keep in mind that this bracket was used on BB as well. Many ebayers won't look up the part number.

http://www.mercruiserparts.com/Show...&bdesc=CARBURETOR/THROTTLE+LINKAGE+(4+BARREL)


The part number I had for the fuel line was for q-jet, not weber (different fuel inlet position). The fuel line you want should be the part number for the 350 mag with hirise/weber. It is easier to bend that down to meet the lower height of the performer, than to use the part number from an LX and bend it up.

http://www.mercruiserparts.com/Show...=2344&bnbr=60&bdesc=FUEL+PUMP+AND+FUEL+FILTER

18 32-8217611 LINE-FUEL 32-821761T USE WITH 4 BBL. CARBURETOR

 

[Bondo]

Re: Merc 2bbl to 4bbl conversion

The Edelbrock 1409 is an excellent choice

Ayuh,.......

And,....
The 600/650cfm model IS a Spread-bore.......
The 700/750cfm is a Square-bore.....

 

[Mkos1980]

Re: Merc 2bbl to 4bbl conversion

Heres another good post for you to read. http://www.speedwake.com/upload/showthread.php?s=&threadid=52583

Same motor as yours just started off with a 4bbl low rise intake already.

 

[Bondo]

Re: Merc 2bbl to 4bbl conversion

Mkos1980,..........

You Obviously have No forum etiquette,........

Linking to a competing website is UnCool,+ Against the forum Rules here..........

I suggest you go back,+ edit out the links you're posting,...........
Otherwise the Mods just might edit You, as well as your Links...............

 

[Mkos1980]

Re: Merc 2bbl to 4bbl conversion

Unless I read the rules wrong, I see nothing wrong with it. Competing websites? How old are we? There is nothing competing about boating. Its the fun of it and that's it. There is a huge difference from the discussions on this board compared to theirs. If there is good informative information on another website what would help a person decide on an outcome, by all means I am going to post it. Several members have expressed their gratitude from other posts that I have shown in the past.