4.0 to 4.2 Head Conversion

4.0 to 4.2 Head Conversion
jmspreach

jmspreach

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Location
Harrisonburg, VA
Vehicle(s)
'78 CJ7 258 4.2 liter with 4.0 head
I recently bought a AMC 258 i6 / 4.2l liter CJ7 that had been sitting for 9 years and spent some time working on the engine, finally getting it running but discovering it had a burnt valve. I did some research and ended up swapping a 4.0 head onto the AMC 258 i6 / 4.2l motor. It transferred nicely and runs a lot better, but I'm wondering if there is a conversion plate or kit that I can put on the 4.0 intake manifold to adapt to my carb., or a kit for a new carb. I'm currently using the old intake, and everything lined up (with some modifications), but I'd rather use the 4 liter intake to make sure everything is sealed correctly and so I can avoid future problems. Thank you in advance for your help.
 
I think you will find that the 4.0 intake is going to be for fuel injection. I don't recal seeing an intake for a 4.0 with a carbureter.:cool:
 
My question is, can a 4.0 intake run carbureted, or do I have to stay with the AMC 258 i6 / 4.2l intake. I know guys that have had 4 liter jeeps they've converted over to carb., I basically want to do the same thing without having to change all the electronics.
 
Why would they do that?? Anybody??:cool:

jmspreach said:
My question is, can a 4.0 intake run carbureted, or do I have to stay with the AMC 258 i6 / 4.2l intake. I know guys that have had 4 liter jeeps they've converted over to carb., I basically want to do the same thing without having to change all the electronics.
Click to expand...
 
You are stuck using an aftermarket intake or an AMC 258 i6 / 4.2l because the 4.0 intake was specifically designed for muti port injection and has injector holes in each intake port.....the other guys are suggesting as am I that your jeep will run better in all weather conditions if you convert your AMC 258 i6 / 4.2l to run the factory 4.0 injection system. It is some work and junkyard trips but well worth it. However since you are carbed and not looking to swap continue to run your AMC 258 i6 / 4.2l intake there is nothing wrong with it and nor will leak in the future. happy jeeping :chug:
 
"I know guys that have had 4 liter jeeps they've converted over to carb."
This is the part I did not understand. I believe I said "they" not "you".
Regardless, this looks like just what you are looking for
.http://www.cliffordperformance.net/...de=CP&Product_Code=47-4520&Category_Code=J258

Read more: http://www.jeep-cj.com/forums/f2/4-0-4-2-head-conversion-7179/#ixzz17NEAy4iq

jmspreach said:
My jeep wasn't currently fuel injected, my AMC 258 i6 / 4.2l is carbureted, but I'm using a 4.0 head and intake on the AMC 258 i6 / 4.2l jeep. I'm not going from fuel injection to carb. If you had read fully my original post you would have understood.
Click to expand...
 
jmspreach said:
My jeep wasn't currently fuel injected, my AMC 258 i6 / 4.2l is carbureted, but I'm using a 4.0 head and intake on the AMC 258 i6 / 4.2l jeep. I'm not going from fuel injection to carb. If you had read fully my original post you would have understood.
Click to expand...

Hey man he did read your post. You said you knew people who converted 4.0s to carbs.

The question is why would someone do this? I mean I can understand carbing a 4.0 or AMC 258 i6 / 4.2l /4.0 hybrid if you were installing in a vehicle that never had the injection. But to take one and cut off the injection and put on a carb?
 
jmspreach said:
My jeep wasn't currently fuel injected, my AMC 258 i6 / 4.2l is carbureted, but I'm using a 4.0 head and intake on the AMC 258 i6 / 4.2l jeep. I'm not going from fuel injection to carb. If you had read fully my original post you would have understood.
Click to expand...
whoa easy we didn't say yours was already fi, you stated that you had some buddies that had carburated 4.0 motors, well factory those motors are fuel injected, we were just wondering who would do that.
 
Thanks everyone for your help. I wasn't trying to be a jerk, I just thought maybe you didn't understand what I was trying to do. Everyone I talk to about this conversion seems to think I've got a 4.0 I'm converting to carb. and they try to sell me things to bypass the crank signal, and stuff I don't need. I do appreciate all the input and I think I will stick with the AMC 258 i6 / 4.2l intake for now. Alot of this is new to me, all I've owned before was cherokees and they've pretty much been stock, so I'll be looking for more input in the future. Thanks again.:)
 
I have a question, was there ever a 4.0 that was TBI rather than MPI??
It would be kind of cool to have one of those manifolds if such a thing existed.
 
IOPort51 said:
I have a question, was there ever a 4.0 that was TBI rather than MPI??
It would be kind of cool to have one of those manifolds if such a thing existed.
Click to expand...

nope
 
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