4.0 head upgrade on 4.2

[Sasquach]

I am getting ready to pull the trigger on a 4.0 head swap and follow it up with either the Howel or idealy the Mopar fuel injection. I have been researching the head and you can go a number of way's from a salvage yard head all the way to a Hesco alluminuim head at $1995.
Anyway I know this has come up before but thought I would clear this so called "myth" up. (ripped from JP mag.)
Head Games
Myth: The '91-'95 7120 casting number are hands-down the best power producers, followed by the '96-'98 0630 and then the '99-up 0331s. The early heads have far superior flow numbers and resist cracking better than the later heads and will make way more power.
Our Thoughts: We don't argue the flow numbers of the '91-'95s are the best, but the later-model HO head flow numbers are generally within 10cfm at the crucial mid-lift areas. Given the conservative factory camshafts, that 10cfm isn't going to do much. All 4.0L heads feature only moderate flow numbers for performance, but offer high-velocity, which is good for low-mid rpm torque. And any '91-up HO head will absolutely kill any '87-'90 non-HO head.
Claimed Gains: 30hp
Actual Gains: 5-10hp
Notes: With the relatively small duration, low-lift factory camshafts there's not much need for cylinder heads with huge flow numbers. The factory heads are well matched to the factory components. It's only when increasing camshaft duration and lift profiles that aftermarket aluminum or ported 7120 heads show their true advantage..

 

[81laredo]

just to pollute the issue, cannot similar results be obtained by Porting and Polishing the original AMC 258 i6 / 4.2l head?

 

[IOPort51]

just to pollute the issue, cannot similar results be obtained by Porting and Polishing the original AMC 258 i6 / 4.2l head?

I say no, the ports on the 4.0 are larger and straighter as I recall.
I replaced mine on the J-10 because the original head was cracked; it is something that AMC 258 i6 / 4.2l heads do. If you start looking through the yards for a AMC 258 i6 / 4.2l head you will go through a few die-pen or mag-flux sessions before you find a good core to work with.
I got one from the outfit in Orlando with the E bay site, at the time they didn’t want a returned core. It had been welded in the chamber between the valves and re machined. I have better than 1ooK on it with no issues so far.
I don’t think I would think about a cam or TBI with out the 4.0 head. IMO the three together would make a major difference. Ordinarily I like to do engine mods one at a time so I can see what gave me the most bang for the Peso but I think it is logical to do these things as one move or perhaps head and cam and then TBI.

 

[Sasquach]

The intake ports are in a line above the exhaust ports on 4.0 and this gives it a more direct and downward path into the comb. chamber(thats the theory anyway). That is the same reason you canot intermingle the manifolds on the two, one works but the other does'nt.

 

[Cheepjeep85]

have you considered one of these Alabama Cylinder Head CHR640N - NEW! 4.0L Cylinder with Valvetrain for 91-06 Jeep® Wrangler YJ, TJ, Unlimited & 91-04 Jeep® Cherokee XJ, Grand Cherokee ZJ, WJ - Quadratec although if it were me i'd find a good junk yard donor and have it reworked, 3 angle valve job, new springs, port and polish, and it should still be cheaper and better flowing than the new stock alabama cyl. head. personally i already have a complete 4.0 that came out of my uncle's 92 yj that i'm gonna use, can't beat free. i'll be putting in another new cam, and maybe the jy tbi, although i might stick with the mc2100

 

[IOPort51]

The one from Orlando has the water jacket welded and it may very well have 3 angle valves for $400 and core.

 

[Sasquach]

I did check ebay and there were some ofered from Orlando Fl. and very reasonable 4-5 hundred plus core w/fuse welded water jackets. ready for AMC 258 i6 / 4.2l conversion. Not sure about the 3 angle grind but would think it's the norm for a machined head?
Oh, and yes to the Alabama head, they make good sense too.
Around here junk yards are rare and not a good option for parts

 

[Cheepjeep85]

3 angle valve jobs are not really standard by anyone unless you are buying a perfomance set of heads or in this case head. i would suggest putting an ad on cl wanting to buy a head from 91-95 wrangler or cherokee. anytime ive needed anything and couldn't find it ive put it in ad and stuff just starts coming out of the woodwork. take for instance this past weekend the rearend went out in my little bros 79 chevy he just bought we couldn't find one with the specific set of gears so i put an ad on cl and about 2hrs later a guy called me up with exactly what we needed went and checked it out and it was a good rear axle at a hell of a price

 

[73CJ]

I did a 4.0 head. Comp FI cam and Holley Projection. The best part was the Holley. It doesn't stall out like the 2BBl did at the top of hills. A little more power, but nothing like a V8.

IMO if you really want HP, go V8. It would be cheaper. How much HP does one really need in a light weight CJ?

 

[Sasquach]

Not looking for v8 power at all, just want a clean/correct running engine with modest power. Being in Ca. it needs to be smog tested so the only logical way is fuel injection and if doing that you should really do the head as well.
Yes I know there would be cheaper ways about it but put Ca. in the mix and things get complicated.
I have been asking myself lately why did I not just buy low mile Rubicon and be done with it? I am fast approaching and will pass what I could have bought a nice one for.
Do like the old school CJ thing and not everyone has a nice one but cheap they are not.

 

[73CJ]

I missed the CA. Understand. Something about a AMC 258 i6 / 4.2l .

 

[xj287]

I'm in the process of doing the 242 head/EFI upgrade on my CJ7 . But trying to keep it as close to $0. as possible has been interesting! For the most part I've just been using left over parts from other projects, and what ever else I can salvage from the parts rigs behind my shop. So far the parts list is '88 RENIX head, '95 intake and exahst manifolds, '92 XJ PCM, wiring harness and fuel lines, and '94 XJ gas tank and sender. Besides a couple gaskets and the distributer, I should have every thing on the shelf already.
Now I have a question....has anyone ever run an EFI AMC 258 i6 / 4.2l on a dyno and see what kind of HP and torque numbers they actualy put out?

 

[IOPort51]

I have never even heard of any one actually doing a dyno on this. With the possible exception of the build up in JP ragazine on the 4.0 nascar/NHRA high RPM boat anchor.:barf:

I'm in the process of doing the 242 head/EFI upgrade on my CJ7 . But trying to keep it as close to $0. as possible has been interesting! For the most part I've just been using left over parts from other projects, and what ever else I can salvage from the parts rigs behind my shop. So far the parts list is '88 RENIX head, '95 intake and exahst manifolds, '92 XJ PCM, wiring harness and fuel lines, and '94 XJ gas tank and sender. Besides a couple gaskets and the distributer, I should have every thing on the shelf already.
Now I have a question....has anyone ever run an EFI AMC 258 i6 / 4.2l on a dyno and see what kind of HP and torque numbers they actualy put out?

 

[xj287]

hmmm might be worth doing then. When mine is all back together I might just have to strap mine to the dyno and see what she does.

 

[IOPort51]

If at all possible, do it in stages so you know what part was the most effective?
I know it will be difficult to do that way but it would be great to actually know what the 4.0 head gets you and what the EFI gets you.

hmmm might be worth doing then. When mine is all back together I might just have to strap mine to the dyno and see what she does.

 

[Cheepjeep85]

only jeep ive ever seen on a dyno, other than the jp article, was on trucks on their cheap cherokee build, it had a 4.7 stroker in it and it made decent numbers can't remeber them exactly, but it was decent. personally i think i'd rather swap in a v8 as to spend that kind of money on a 6cyl

 

[LongHorn]

only jeep ive ever seen on a dyno, other than the jp article, was on trucks on their cheap cherokee build, it had a 4.7 stroker in it and it made decent numbers can't remeber them exactly, but it was decent. personally i think i'd rather swap in a v8 as to spend that kind of money on a 6cyl

X1000 on that!
My point exactly.

 

[Sasquach]

For Ca. anyway we just can't drop in the most HP per $ and be happy, we have to make more HP while keeping the smog police happy and going to a V8 not an option for Jeeps after 1975 but modifying your AMC 258 i6 / 4.2l to newer more efficient 4.0 specs can work.
By the way what sort of weight do you add going to say a 350 ?

 

[Cheepjeep85]

i wouldn't think it would be a whole lot more i mean the AMC 258 i6 / 4.2l is a pretty heavy motor. if i had a guess i'd say maybe AMC 150 lbs more if that

 

[LongHorn]

for ca. Anyway we just can't drop in the most hp per $ and be happy, we have to make more hp while keeping the smog police happy and going to a v8 not an option for jeeps after 1975 but modifying your AMC 258 i6 / 4.2l to newer more efficient 4.0 specs can work.
By the way what sort of weight do you add going to say a 350 ?

i wouldn't think it would be a whole lot more i mean the AMC 258 i6 / 4.2l is a pretty heavy motor. If i had a guess i'd say maybe AMC 150 lbs more if that

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