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Discussion Starter · #1 ·
I am doing an engine swap. When Jeep changed from the 4.0 to the 4.2 did the intake manifold dimentions change at all. What I am wondering is if I can use an intake from a 4.2 on a 4.0 ? Will it work?

91 YJ swaped in 4.0L 2 inch lift. (work in progress)
 

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Discussion Starter · #2 ·
In respect to the question about the manifold, I know that putting a 4.0 where a 2.5 used to be is a common swap. Has anyone done this swap, How did the cooling system work out. Did you have problem with overheating with the larger motor. Does anyone know, or have any thoughts?

91 YJ swaped in 4.0L 2 inch lift. (work in progress)
 
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I need to ask why?
Jeep actually went from the older, carbed, 4.2 to the newer, injected 4.0. Putting newer 4.0 HO upper engine stuff onto the older 4.2 block makes a good combo, but why would you want to choke your existing 4.0 with the old carbed intake?
They are basicly a bolt on swap for one another but the 4.2's top end is more restrictive than the 4.0's


'88 Sahara, 4.2, auto, 4.0 head swap (finally), no trac bars.
 

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Some people can't afford the fuel injection components, or like myself, are content with carburated performance and simplicity.
The biggest single performance upgrade for the 4.2 has to be the 4.0 head swap, and it's pretty cheap, easy, and quick with appreciable gains even for folks with carbs.
Bob in Ma

 

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Carbing a 4.0L HO head is more common than you'd imagine.
The biggest obsticle in mating the old intake on the new head is usually needing to find some larger diameter heavy washers or horns to fill the gap between the old intake and the required 4.0 style exhaust manifold.
The newer aluminum 4.2 intakes are better breathing but I've had no reports as to sucess of mating one of these over the older cast iron versions.
In either case, I might suggest holding a 4.0 intake gasket over the 4.2 intake and see if you could do a little 'match porting' - especially around the head's injector bump up.
Tip: According to Bennie at HESCO, Permatex "Ultra Copper" gasket sealer is about the best if you care to use anything on the gaskets.
Note: It is said that any silicone based compound is hell on the O2 sensor so ... "a little dab will do ya" ... use only a very thin coat if you use anything.
Tip: Fel-Pro exhaust gaskets are about the best out there. Each port hole has a metal squeeze ring and using a compound is unnessesary.
Tip: CJDave always endorses using studs and double nuts instead of regular manifold bolts.

JAF
http://www.monsterslayer.com/jeep
 

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Discussion Starter · #7 ·
The reason why I am looking into this is because of the cost of FI. I just can't afford it. And the wiring and computer set up is too complicated for me. I would much rather have the simple carb. And I have an old 4.2 that will not run. So taking the parts off of it is all but free. Thanks everyone for you help.
Does anyone know about the cooling? Still trying to figure that out.

91 YJ swaped in 4.0L 2 inch lift. (work in progress)
 
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