4.2/4.0 ?

[81laredo]

I bought an '81 CJ7 recently to replace my '59 CJ5 and have a few questions. The '81 has the in-line 6 with 4 speed and is as far as I can tell still a stock CJ7 Laredo . I want to replace the Carb with Fuel Injection, primarily to get rid of all the Vacuum Lines! (I m in California)
My 1st question is about he AMC 258 i6 / 4.2l and the 4.0 in-line 6. Is there much of a difference between these Engines? They look to take the same Head Gasket and Intake Gaskets so one may assume that they are very close.
It does make sense to start with the better platform because of the $$$ spent on Fuel Injection but there is no reason to throw away a good Engine.
Thanks in advance,
Steve

 

[Cheepjeep85]

you can use the 4.0 head on the AMC 258 i6 / 4.2l block. you can also take the rods and crank out of a AMC 258 i6 / 4.2l and put em in a 4.0 for a 4.6 stroker motor. there are alot of write ups on the web on how to do this. plus junkyard tbi swaps, howell fuel injection, or the way more expensive mopar mpfi kit

 

[CoreyYoungCj577]

I bought an '81 CJ7 recently to replace my '59 CJ5 and have a few questions. The '81 has the in-line 6 with 4 speed and is as far as I can tell still a stock CJ7 Laredo . I want to replace the Carb with Fuel Injection, primarily to get rid of all the Vacuum Lines! (I m in California)
My 1st question is about he AMC 258 i6 / 4.2l and the 4.0 in-line 6. Is there much of a difference between these Engines? They look to take the same Head Gasket and Intake Gaskets so one may assume that they are very close.
It does make sense to start with the better platform because of the $$$ spent on Fuel Injection but there is no reason to throw away a good Engine.
Thanks in advance,
Steve

This is a good article Swapping in a 4.0L High Output MPI Engine to Replace a 258 Carburetored Engine the guy says its one of the easiest swaps, the only other thing i would think you need to do is maybe look at advance adapters for an adapter for your Transmission . let me know i this helps!

 

[81laredo]

It sounds to me as if the AMC 258 i6 / 4.2l and the 4.0 are similar engines. As long as this is correct I will most likely use the AMC 258 i6 / 4.2l Block.
Does the 4.0 Head have an advantage over the AMC 258 i6 / 4.2l ?

 

[elwood blues]

It sounds to me as if the AMC 258 i6 / 4.2l and the 4.0 are similar engines. As long as this is correct I will most likely use the AMC 258 i6 / 4.2l Block.
Does the 4.0 Head have an advantage over the AMC 258 i6 / 4.2l ?

It's made of aluminum not cast iron and the intake and exhaust runners are a larger diameter.

 

[Cheepjeep85]

if you have a good motor in that jeep i don't see swapping the whole thing out just for fuel injection that could get a little pricey. but its your choice the head swap is real easy i plan on doing it sometime in the next 6 mo i already have a head and i'm looking for all of the parts for the junkyard tbi. maybe someone who lives in cal can chime in and tell you if will pass emissions as i live in ga and don't have a clue about that

 

[Cheepjeep85]

they say you gain 40hp by doing the head swap because it flows so much better

 

[Petescj]

Lots of good reading right here.

CJOffroad.com - 4.0 Swap Information

 

[81laredo]

40 Hp? that is expecting allot out of a 110 Hp Engine (from this forum) but anything close to that would make that change well worth the $$$$

 

[CoreyYoungCj577]

40 Hp? that is expecting allot out of a 110 Hp Engine (from this forum) but anything close to that would make that change well worth the $$$$

Atleast you have the 110 hp engine mines pushing a whole 90-100 i think its a 232ci

 

[IOPort51]

I would go with the head swap. The head gasket is different and you have to fill some of the water jacket holes. The head does improve things but I have never seen an actual Dino test on this and I think 40 hp may be a bit optimistic. I would question the legality of the use in Cali. but can't say for sure. The AMC 258 i6 / 4.2l intake works but you have to use the 4.0 exhaust. Lots of good wright ups on this one.
The most bangs for the peso I have gotten , power wise, was the TFI ignition upgrade. New coil, wires cap and rotor, It was very surprising.

 

[BrockGrimes]

Check out post# 15:
http://www.jeep-cj.com/forums/f49/useful-info-thought-id-share-665/

All you'd ever want to know about the 4.0 head swap.

 

[Cheepjeep85]

yeah 40 hp does sound like alot but thats what alot of people claim. i figure if it gives anything close to 20 hp and maybe a little better mpg then its well worth it