4.2 to 4.0 head/MPI is underway!

[ThisGuyUKnow]

Haha i dint mean post it here lol hopefully mopar wont get upset lol

Thats pretty much a step by step that could work with the new setup or you could just substitute junkyard parts.

 

[Sasquach]

Haha i dint mean post it here lol hopefully mopar wont get upset lol

Thats pretty much a step by step that could work with the new setup or you could just substitute junkyard parts.

I was unable to paste the link for some reason(comp. challanged at times)
This is the old version but little has changed.

 

[stoney]

Before you did the 4.0 and mpi install did your engine ping?

 

[Sasquach]

Before you did the 4.0 and mpi install did your engine ping?

No...If you ask because I mentioned "no pinging" on my post install results it's because there had been issue with that on some installs with modified motors.

 

[stoney]

My jeep pings now with premium gas (mostly in the higher speeds 55+). Timing did not make a difference. Thats why I wanted to do the head swap when a did fuel injection thinking it would solve that. I would be one annoyed person to put the head and f.i. and still have it ping. ???? I am figuring it's because of the carter carb and all the old emissions ??? One personal question why did you choose mopar over howell with 4.0 head

 

[stoney]

I mean the AMC 258 i6 / 4.2l head, carter bbd, old emissions. The ping is what is delaying the jump to fuel injection already. Any thoughts? (Other than the ping my jeep runs great. starts, runs, sounds good and strong - Purrs like a kitten... that is slightly congested!

 

[Sasquach]

stoney, I see you are just over the hill from me in the valley. Pinging is something I can't see a stock AMC 258 i6 / 4.2l on emisions doing?
Well anyway if you go MPFI you get to yank ALL the emissions off and you would be surprised at how well your rig runs!
I went Mopar because it made the most sence to me, junk the emissions and produce the most HP in one easy but somewhat costly effort.
My opinion of doing the MPI without doing the head would be a waste as the AMC 258 i6 / 4.2l head is dinasour compared to the 4.0 head.
Mopar over Howell? multiport is superior to throttle body injection.

 

[stoney]

Yeah, I am just over the hill. Any chance I can check out your rig. I am all for the mopar and the head. I have never met anyone with this set up. I would appreciate it :. I really feel this will give me everything that I am looking for (power, reliablilty, improved gas milage, and no more smog worries!) as well as justify all the money I have "INVESTED" into my Jeep.

 

[Sasquach]

Yeah, I am just over the hill. Any chance I can check out your rig. I am all for the mopar and the head. I have never met anyone with this set up. I would appreciate it :. I really feel this will give me everything that I am looking for (power, reliablilty, improved gas milage, and no more smog worries!) as well as justify all the money I have "INVESTED" into my Jeep.

Sure can, PM me and will go from there.

 

[ThisGuyUKnow]

My jeep pings now with premium gas (mostly in the higher speeds 55+). Timing did not make a difference. Thats why I wanted to do the head swap when a did fuel injection thinking it would solve that. I would be one annoyed person to put the head and f.i. and still have it ping. ???? I am figuring it's because of the carter carb and all the old emissions ??? One personal question why did you choose mopar over howell with 4.0 head

If you did a tbi setup you would still have a wet intake. With MPI you have the injectors basically squirting the fuel straight at the intake ports. It basically just ensures that you have even fuel flow to every cylinder. With a carb or TBI the outer cylinders get a leaner mixture no matter how well you tune it because the injection site is centered in the intake and you pretty much have to depend on gravity and the natural vacuum of the engine to deliver fuel to the cylinders. TBI is still a very good setup and has many benefits over the carb because the carb relies on the vacuum to deliver fuel into your intake manifold whereas the TBI uses the computer and electric injectors to feed your engine and a TBI setup can be had for a much smaller fortune than a the mopar kit.

If you wanted to do the MPI I suggest cruising some part out threads. i have 2 extra 4.0 intakes (one is a 99+ horseshoe style that is supposed to flow better but needs to be welded in a spot) My dad was the one who did the wiring in my swap (worked as an electrician for the USMC for 23 years) and if you can get a hold of a wiring harness from a 1994 cherk like we used I may be able to get him to write a how to on what to do to get the harness to work, or if push come to shove he may be willing to edit one for you.

Not knocking the mopar kit but there is a definite monetary advantage to junkyarding the system.... I am not from CA and have never had to go head to head with the smog nazis but I believe that you can talk to the referee(is this the right term?) and tell them that you just swapped a 4.0 for whatever year your harness donor is(how will they prove you still have a AMC 258 i6 / 4.2l bottom end?) and then they will have to pass smog as if you were running that year vehicle??? I know the Mopar kit automatically comes with some sort of smog nazi sticker or something... I hope I never have to deal with them.

Which ever way you want to go we can help you through it

 

[Rescue Diver]

I'm at work so I don't have enough time to read the whole thread and maybe this was already answered. What year AMC 258 i6 / 4.2l are you using? I noticed the mopar instructions said the kit is for 1981 and newer. Will a 4.0 head work on a pre 1981 AMC 258 i6 / 4.2l ?

I just rebuilt my AMC 258 i6 / 4.2l shortblock and head that came from a 1978 CJ so I'm not looking to upgrade any time soon, but I'd like to know if the 4.0 head will work on the shortblock I already rebuilt in case I decide to upgrade later. Yours looks exactly the same as mine from what I can tell from the pics.

P.S. Awsome Job!

 

[Sasquach]

I'm at work so I don't have enough time to read the whole thread and maybe this was already answered. What year 258 are you using? I noticed the mopar instructions said the kit is for 1981 and newer. Will a 4.0 head work on a pre 1981 4.2?

I just rebuilt my 258 shortblock and head that came from a 1978 CJ so I'm not looking to upgrade any time soon, but I'd like to know if the 4.0 head will work on the shortblock I already rebuilt in case I decide to upgrade later. Yours looks exactly the same as mine from what I can tell from the pics.

P.S. Awsome Job!

It's a 78 AMC 258 i6 / 4.2l . The Mopar kit was originaly carb approved for 81-on because of the needed oxygen sensor in the exhaust(told that by Hesco) although it has since been carb approved for all year AMC AMC 258 i6 / 4.2l engines and most retailers have not realized this and changed there advertising. I was actually the one who dug up the latest executive order and brought it to Hescos attension that it was Ca. legal pre 81 year.
Yes the 4.0 head will work on your block and is a very worthwhile upgrade.

 

[ThisGuyUKnow]

It's a 78 4.2. The Mopar kit was originaly carb approved for 81-on because of the needed oxygen sensor in the exhaust(told that by Hesco) although it has since been carb approved for all year AMC 4.2 engines and most retailers have not realized this and changed there advertising. I was actually the one who dug up the latest executive order and brought it to Hescos attension that it was Ca. legal pre 81 year.
Yes the 4.0 head will work on your block and is a very worthwhile upgrade.

Remember some 258s have smaller head bolts than the 4.0s and require bolt spacers

 

[Sasquach]

Remember some 258s have smaller head bolts than the 4.0s and require bolt spacers

Yes and you also can rethread the block and use larger 1/2" bolts if you like. Rescue Divers 78 should have the 1/2" bolts though and no worries.

 

[ThisGuyUKnow]

Yes and you also can rethread the block and use larger 1/2" bolts if you like. Rescue Divers 78 should have the 1/2" bolts though and no worries.

I know just wanted to make sure that was said for other people looking for info on the swap

 

[DirtyB]

I would like to do the 4.0 head swap like y'all did here, but I'm concerned that the increase in compression ration will cause it to ping. How is it that your compression ration increases, but you don't need to run higher octane gas?

Just curious, would I be better off just swapping in a complete 4.0? Is there any significance in HP or torque? I've heard some guys say that swapping out the entire engine may be easier.

I'd REALLY like to get away from the carb. I'd REALLY like to get some more HP. I have problems uphill against the wind over 55 MPH.

 

[Sasquach]

Mine would barely ping under load with too much throttle and it went away with a half and half (reg/prem) mix but I just run premium and forget about it. What's a few cents per gallon.
I would do it all over again the same way and obviously very happy with the outcome but in Ca. my options were Limited due to smog testing, everyone needs to look at it to suit their circumstances. Do you have to smog test, are engine swaps allowed, is your AMC 258 i6 / 4.2l bottom end solid enough to modify, etc.
As far as swaping the entire engine being easier? I think not, how hard is it to bolt on a new head? All the rest of the intake and exhaust work would be the same regardless of what short block is under it.

 

[DirtyB]

Actually, when you are relatively poor like me, a few cents does make a difference.

But, it sounds like you are giving me good news. Hopefully if I do this swap, I'll get more horses, torque, gas mileage, etc. I'm wanting to get away from the carb also. It's a little to finicky even though I upgraded a few years ago to the MC2100.

I'm going to start looking for a used head tomorrow!

Thanks for the help.

 

[Rescue Diver]

The swap only brings you up to a little over 9 to 1 compression. I just run regular unleaded and it doesn't ping at all. Just make sure you set your ignition timing so that it's advanced as far as it can go without pinging. It's really that simple. I've put a lot of miles on mine and haven't had to do anything other than change the oil every three thousand miles. It still runs as good as the day I bolted it together, and I never have to worry about maintaining highway speeds into the wind on long uphills. The greatly increased gas mileage is also a huge bonus!

Good Luck!

 

[Rescue Diver]

Actually, when you are relatively poor like me, a few cents does make a difference.

But, it sounds like you are giving me good news. Hopefully if I do this swap, I'll get more horses, torque, gas mileage, etc. I'm wanting to get away from the carb also. It's a little to finicky even though I upgraded a few years ago to the MC2100.

I'm going to start looking for a used head tomorrow!

Thanks for the help.

Be sure and get a 4.0 head that was made before 1999! The castings that were made between 1999 and 2001 tend to crack at around 120,000 miles between two of the combustion chambers. The 1991 to 1995 is the easiest swap because it already has the temp sender hole at the rear behind the valve cover.