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Putting 80s 258 2 barrel intake on 76 engine - wha

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mantonas View Drop Down
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    Posted: Jul/10/2016 at 12:25am
I am trying to convert the 258 cubic inch AMC six on my 1976 Pacer from one barrel to two barrel carburetion. I bought a two barrel intake on eBay. The part number is EF3237858. According to a different eBay listing (take this information with a grain of salt), here are the vehicles that EF3237858 was used on:

INTAKE MANIFOLD 258 4.2L EF3237858

CHEROKEE 81-83 6-258 (4.2L)
CJ-SERIES 81-86 6-258 (4.2L)
CONCORD 81-82 6-258 (4.2L)
CONCORD 83
EAGLE 81-84 6-258 (4.2L)
EAGLE 85-88
GRAND WAGONEER 84-86 6-258 (4.2L)
J-SERIES TRUCK 82-87 6-258 (4.2L)
SPIRIT (AMC) 81-82 6-258 (4.2L)
SPIRIT (AMC) 83
WAGONEER 81-83 6-258 (4.2L)

This manifold has EGR, which I plan to block off, since my 76 engine doesn't have it (plus I live in Tennessee). It also has numerous vacuum fittings and sending units, which I will probably remove and plug. However, the most interesting and puzzling thing about it is that it has a water jacket for engine coolant. My 76 one barrel manifold has nothing of the sort. I guess I could just not use the water jacket and leave it open to atmosphere, or plug those ports too. 

What was the purpose of this, to accelerate heating up the interior of the car on cold days, or to provide some heat transfer away from the intake and exhaust manifolds? Is it a good idea to incorporate this water jacket into the heater hose routing? Would anything bad happen if I just plug these? Does the presence of this water jacket have anything to do with the fact that this manifold is aluminum, versus cast iron for the one barrel I have that doesn't have them? Also, the two barrel manifold has one of those electric fuel warmers below where the carb mounts that looks like a bunch of pins sticking up. Should I use that? Does it have anything to do with why there's a water jacket in the manifold?

Thanks all. 
1976 AMC Pacer X
1978 AMC Pacer V8
1987 Jeep Grand Wagoneer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pdok Quote  Post ReplyReply Direct Link To This Post Posted: Jul/10/2016 at 8:56am
The water part is good to use. The heated part is good too but may not matter depending on climate where you are. On a jeep the heated plate reads oil pressure to determine if the motor is running and I believe also coolant temp. It will turn off if the motor stops or coolant is hot enough. I never used mine on my 76 and our team great even in the cold.

You know you're going to have to change exhaust manifolds right?

I used epoxy to block egr on mine.
76 Grem X 258/904,4.0 head/MPFI, Comp X250H cam, Hughes springs, Clifford header, serpentine swap.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mantonas Quote  Post ReplyReply Direct Link To This Post Posted: Jul/10/2016 at 9:10am
I didn't know that I would need to change exhaust manifolds. I'm glad I posted this question. I need to replace the mainfold gasket because there's an exhaust leak, so I thought since I had the intake manifold off anyway it would be a freebie to install this manifold. Sounds like I was wrong. Thanks for setting me straight.

Assuming I got a matching exhaust manifold and did the swap, what would be the recommended routing of heater hoses for this manifold? Would I just interrupt the hose that comes out of the thermostat housing?
1976 AMC Pacer X
1978 AMC Pacer V8
1987 Jeep Grand Wagoneer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jul/10/2016 at 9:51am
Go from the feed to the heater (block connection) to the front of the intake, then from the rear of the intake to the heater core. Return line from heater core goes straight to the water pump.

You don't have to use it, but the heat helps a lot with cold weather driving and helps economy by vaporizing the fuel better. Drag racers do the opposite -- they want a cool intake to improve fuel density and power -- can get a bit more air/fuel in. For a normally driven street car better vaporization of the fuel is more important for economy than 2-3 more hp.
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pdok Quote  Post ReplyReply Direct Link To This Post Posted: Jul/10/2016 at 1:23pm
Exhaust from any 258 of that vintage as your intake should work. I'm assuming your 76 was stock with the bolted connection between intake and exhaust. You might have to mess with linkage and exhaust pipe too.

The water passages help with restarts when intake has cooled but water is still warm. The heat plate helps for cold starts. I had no real problems starting mine at 20 degrees F with no heat plate. Had to wait a couple minutes and not floor it at first of course.
76 Grem X 258/904,4.0 head/MPFI, Comp X250H cam, Hughes springs, Clifford header, serpentine swap.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mantonas Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2016 at 7:34am
My exhaust system is shot anyway so no problem if it needs to be modified.

Seems to me that there would be some loss of rigidity or structural integrity to the manifolds if they are not bolted together. Having them hanging off the side of the block individually seems like it would cause them to move up and down more easily. Did the factory cars with the later 258s that used independent manifolds (like the 2 barrel one I am trying to install) come with some kind of support bracket or brackets? If so, could I grab it off a Jeep with a 4.0 from the junkyard?

1976 AMC Pacer X
1978 AMC Pacer V8
1987 Jeep Grand Wagoneer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote uncljohn Quote  Post ReplyReply Direct Link To This Post Posted: Jul/11/2016 at 9:49am
Originally posted by mantonas mantonas wrote:

Seems to me that there would be some loss of rigidity or structural integrity to the manifolds if they are not bolted together.


The exhaust and intake manifolds on your engine were bolted together because the bottom of the intake manifold was the top of the exhaust manifold where the heat from the exhaust was used to heat the intake. Structural rigidity had nothing to do with it. They later manifolds will stay in place just fine!

The later manifolds just used heat from the cooling system of the car rather than exhaust heat to do the same thing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote FSJunkie Quote  Post ReplyReply Direct Link To This Post Posted: Jul/18/2016 at 1:52am
258 1bbl was rated at 110hp.
258 2bbl was rated at 115-120hp.

We're talking the difference between 175 CFM and 195 CFM. You're also going from a really simple carburetor (YF) to a more complex and notorious for trouble carburetor (BBD). Is it really worth it for 5-10 horsepower? Your air conditioning or power steering pull that much power.

Plus you should change the exhaust manifold with it and should find a way to wire up the 2bbl intake's electric manifold heater and water heating apparatus because unlike the 1bbl intake that has a built-in heat stove, those are the 2bbl intake's only methods of improved fuel vaporization for cold weather.



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'72 Wagoneer: 360/TH400/3.31
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'77 Hornet: 232/TF904/2.73
'84 Eagle: 258/TF904/2.73
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DaemonForce Quote  Post ReplyReply Direct Link To This Post Posted: Jul/18/2016 at 3:37am
I have NO idea what you're going on about. The stock 258 intakes I've seen all have some electric heating pot on the bottom and utilize coolant passages that run through the intake casting. I've never had much trouble with the Carter other than the stepper motor. I eventually scrapped most of it to partially rebuild and swap in a straight downdraft model. The amount of work I did to make it work was a bit more engineering than I care for. Use a Motorcraft 2100.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Jul/18/2016 at 7:02am
I'm assuming you're talking about FSJunkie's comments, DF. The "electric heating pot" is what he's talking about. It helps speed warm-ups. As long as you don't mind babying the car a bit for the first 10-15 minutes of driving you're okay without it. I'd use the water passage anyway.

I agree -- the BBD can be a PITA. Most of the non-computer ones are old and can be worn to the point a simple rebuild isn't enough. The computer models need everything else to be working correctly if the stepper motor still works. I'd recommend a Motorcraft 2100 also, or some newer model like the popular Weber conversion.

FSJunkie did point out that a 2V carb isn't going to do a whole lot by itself though. 10-15 hp is about it -- 20 if you're lucky. What the AMC six really needs is a better cam to support a bigger carb. Isky 256 Supercam is one of the better ones, or a Comp 260H.  Comp Xtreme cams aren't really intended for street vehicles.
Frank Swygert
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