2 barrel to 4 barrel change


Old 11-20-07, 07:27 AM
borak's Avatar
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2 barrel to 4 barrel change

I have a 68 Ford LTD hardtop 4 door with a 390 big block. The 390 currently has a 2 barrel carb on it. My intention is to rebuild the motor and I want to go to a 4 barrel carb. I know I'll be swapping the carb and intake. Is there something else I need to do for the swap? What size 4 barrel should I get? Gas mileage isn't a concern.

I've thought about changing the bore and stroke to make it a 427 but think I want to stay with the 390.
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Old 11-20-07, 08:25 AM
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You own an oil well, I hope?
Old 11-20-07, 09:19 AM
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If you do nothing but change the intake and carb, you probably will see minimal gain in performance.

The biggest mistake people make in trying to get better performance is mismatching combinations. That motor displacement, camshaft selected with rpm range, heads, exhaust system, transmission, rear gears, weight of the vehicle and intake system was designed to work together. If the engineers felt it would perform better with a 4bbl and intake, it would have come with it.

Now, that is not saying it wont make more over all power than the 2bbl set up, but at the cost of gas mileage and maybe even low end torque, which is what you need for a big old heavy vehicle.

When you rebuild it, I would suggest you make sure you have at least 9.5:1 compression with good quench, a good valve job on the heads, a cam with a tad bit of more duration @ .050 (say 5 degrees), small tube headers, a good low end torque intake and a 600 cfm vacuum carb.

That build will give you a torque monster and you wont have to worry about converter or rear gear changes.
Old 11-20-07, 10:03 AM
borak's Avatar
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It going to be a gas hogging cruiser. It won't be driven much which is why mileage isn't a concern. Already have collector plates on it. Hopefully after i complete this one I can figure out a way to do my Dad's 70 Mercury Cyclone with the 351 Cleveland.

The LTD was given to me from my Dad for graduating college. He wants to see Dual exhaust on it.

Thank you for the advice. I want to have the 4 barrel on it to increase the power a little. I figured there was more to just swapping but wasn't sure what.

I don't think I'll learn the meaning of gas hog til I get my 472 into something.
Old 11-20-07, 01:39 PM
Join Date: Oct 2000
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I have the shop manual for the 68 Ford LTD. I used to own a 67 Ford LTD.
Old 11-21-07, 04:43 AM
Join Date: Aug 2004
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You may need to replace the

fuel pump. You may need a mechanical pump with a slightly higher flow rate.

If the four-barrel was an option when the car was new, there's probably not much else you need to do. Will the replacement carb be new (rebuilt) or used? If used, unless you pulled it from a car you heard running, I'd plan on re-building it before I installed it again.

Check closely for the little things, such as vacuum ports, choke connections, cooling connections, etc. Make sure the replacement carb matches the old one as closely as possible here.

Fuel lines and throttle linkage, kickdown cables/controls.....not sure here, but check and compare these too. There usually are significant differences between a two barrel and four barrel carb here. For popular engine swaps, you may be able to find a kit that has all the hardware needed.

You'll probably also need to adjust the timing a little.

If you go with a carb with adjustable jets, then you can play with jet sizes to get the best combination of torque vs. RPM.

The last possibility, you may need to replace the fuel lines from the tank to all the way to the pump to allow increased flow. It's pretty rare, but sometimes the lines were under-sized at the factory to begin with.

Hope this helps.
Old 11-21-07, 08:22 AM
borak's Avatar
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The 68 LTD's with the 390 came with both the 2-barrel and 4-barrel setups. The biggest thing to determine on the swap I suppose would be the differences between the 2 car builds.

Thank you for the responds

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