Off Roading Forums banner
1 - 19 of 19 Posts
G

·
Discussion Starter · #1 ·
I've been looking around at a few Cherokees now and most I've found in the best shape are the '90's which are pre-HO 4.0 (which came out in '91) I've done the HO 4.0 head swap on my 4.2 YJ and I'm wondering if it can be done on the earlier 4.0 as well or does the different injection system make the latter HO head not fit.
Just a though.


'88 Sahara, 4.2 that runs thanx to every Cheap trick on this board. The rest is getting there!/wwwthreads_images/icons/blush.gif
 

·
Registered
Joined
·
792 Posts
Sorry Cant answere your question, but I am wondering how you like the 4.0 swap on your wrangler. Was their a noticable power gain. Where did you find the parts(Heads manifolds). How much did they cost you, + total project cost.

79 CJ 5, 258, dana 30, model 20, T18, dana 20, 2.5" rancho lift, 1" shackles
 

·
Registered
Joined
·
2,137 Posts
I don't know of any reason why you can't swap a pre or post 1991 head on either a 4.2 or 4.0 block as long as you address the water jacket issue when using a 4.2 block.
Note that you won't gain much, if anything, by going with the pre '91 non-HO head.
I am curious to know if an '87 to '90 non-HO 4.0 head designed for the Renix injection has raised corner bump up intake port like the 1991 and later HO heads. Anyone?



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

·
Registered
Joined
·
1,705 Posts
Use the HO head. The water jacket setup is different, and will overlap the block. Also, the bolt holes in the head are a different size - the price difference between a 90 head and a 91 should be negligible.

85 CJ-7 258/T176/D300 Scout D44s F&R with Lock-Rites and 4.56 gears. 4" springs with lift shackles 36" SS TSL Radials Hella Rallye 4000s for guiding small planes into the woods
 
G

·
Discussion Starter · #5 ·
Sounds like tony had a clue what I was asking but he didn't know the answer. The answer to tony however is that yes I really like the 4.0 head swap on my 4.2 When I first got the YJ, I could not spend much time on the freeway without thinking I was going to kill the engine because it struggles so badly to keep up to speed. After the swap I can now pass people on the freeway and go up hills. I still have the carb aswell so those that do the whole FI swap have it really good.

Now my original question was whether or not the HO 4.0 head swap could be done to an earlier non-HO 4.0 for example the one found in an '89 Cherokee? Just wondering if it can be done and whether it would be enough of an improvement to warrant the swap.
Thanx


'88 Sahara, 4.2 that runs thanx to every Cheap trick on this board. The rest is getting there!/wwwthreads_images/icons/blush.gif
 
G

·
Discussion Starter · #6 ·
With the 4.0 head on a 258 do you get beter power at all RPM's or does this just move the max touque and power up the RPM curve. In short do you notice an improvement in power below 2000 RPM or is the improvement mostly at higher speeds.

thanks

bandhmo

 

·
Registered
Joined
·
2,137 Posts
Quote: "I don't know of any reason why you can't swap a pre or post 1991 head on either a 4.2 or 4.0 block..."

OK, I'll say it in clearer terms ...
They re-designed the 4.0 HEAD for 1991 but they did not significantly re-design the 4.0 BLOCK so I do not see any reason why you can not put a post 1991 4.0 HO head on a pre-1991 4.0 BLOCK.
And, since you can put a 4.2 intake manifold on a post-1991 4.0 HO head I don't see any reason why you can't install either a Renix or MPFI on a post-1991 4.0 HO head.



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

·
Registered
Joined
·
2,687 Posts
Hey Stooby,

how did the carb intake manifold line up on the 4.0 head swap? What did you have to do to make it line up and bolt down, as the ports are raised on the 4.0 compared to the 4.2.

And how did it affect low end torque?

Tim

84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, 4.56's and Detroit softlocker, full cage & belts, Xenon flares, Dana 44 rear, GM dual diaphragm brake booster
 

·
Registered
Joined
·
1,423 Posts
Every thing that I have read says the intake manifold should line up without a problem. It is the exhaust that gives people fits and you have to change to a 4.0 exhaust manifold or headers. I'll find out when I change mine next month!

My girlfriend said if I spent one more dime on my Jeep she would leave. Man I'm going to miss her!
 

·
Registered
Joined
·
2,687 Posts
One post said he needed oval washers to cover both the holddown for the intake and exhaust which share the same bolts. The two used to line up with the 4.2 head, but are offset on the 4.0L.

Tim

84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, 4.56's and Detroit softlocker, full cage & belts, Xenon flares, Dana 44 rear, GM dual diaphragm brake booster
 
G

·
Discussion Starter · #11 ·
This one opened up a lot of new questions!
1. I don't have any numbers to back this up but I notice a power difference throughout the speed range. The 4.2 is already torquey in the lower RPM's so the swap made the most difference in the higher RPM band but it still seems more drivable at lower speeds aswell. Side note: the TR upgrade made a difference in the high RPM's aswell because with it, the ignition now fires at higher RPM's.
2. The intake manifold was not a problem. On the bottom of the #'s 1 & 2 ports of the intake, there are alignment holes that fit over studs in the head. Under the alignment holes, there are grooves. Once the new 4.0 head is installed, the intake rests with these grooves on top of the studs instead of the studs in the holes. This corrects the port alignment. No modifications.
3. As all the write-up's mention, the exhaust manifold must be changed to the HO 4.0 manifold or aftermarket header. The old 4.2 manifold will not line-up with the 4.0 head.
4. The intake and exhaust are now spaced too far apart for the stock oval washers to span both when bolting them to the head. The easiest solution is to buy larger flat washers (maybe 1.5 inches across) from the local hardware store (.20c each) and use these with the stock oval washers to clamp down both manifolds together. Make sure you get a good strong washer. The flat washer will span over both manifolds while the stock washer over it, will give the clamping force.

Thanx for the clarification on the post Jaffer. I had heard that the renix and Mopar injection systems had different injector ports but that may have just been on the intake manifold.

Anyone have any other questions, just shoot.
I think my total cost was as follows:
H0 4.0 head, used from wrecker - $200
H0 4.0 stock header style exhaust manifold - $100
H0 4.0 stock head gasket kit - $80 (included head, water pump, intake/exhaust, valve cover gaskets and valve seals)
Coolant, oil, oil filter, flat washers...misc... $40
That's all Canadian so for the majority of you that live in the States, that's about $20 bucks. /wwwthreads_images/icons/laugh.gif


'88 Sahara, 4.2 that runs thanx to every Cheap trick on this board. The rest is getting there!/wwwthreads_images/icons/blush.gif
 
G

·
Discussion Starter · #12 ·
hay, i just bbt'd at JEEPBOARD.COM
go to cj5-8.
always stuff in other areas, there, too.
best place for it. sorry, i can't do
the click thing.

when in doubt.........
empty the magazine.
 
G

·
Discussion Starter · #14 ·
the original guys say fill the ports with epoxy.
the more experienced say NO WAY...weld 'em, or they WILL leak, eventually.

i am considering "block fill" and kind of.... filling
that entire are about an inch thick.

.....but then, if it eventaully leaks, it'll be a pita to weld. jury's still out......

when in doubt.........
empty the magazine.
 

·
Registered
Joined
·
2,687 Posts
Best solution I saw was a guy reemed them round and put in small core plugs.

84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, 4.56's and Detroit softlocker, full cage & belts, Xenon flares, Dana 44 rear, GM dual diaphragm brake booster
 
G

·
Discussion Starter · #16 ·
i looked kinda close at that, and they look a little too near the chamber ring on the head gasket.
it would also take extensive setup on a mill.
so far i like the weld and resurface deal.
i was told a copper weld, still tryin to
figger that 1 out, but he's (they've) done
done quite a few....i was just tryin to avoid it all.


when in doubt.........
empty the magazine.
 
G

·
Discussion Starter · #17 ·
I almost did this swap on my 87 YJ, but did a rebuild and Mopar MPI kit instead.

In my research, I found that you need the head with the casting 7120, and not the 8680 casting. There were some differences between the 2 heads, and the 8680 had some clearance issues (it's been a while, and I don't recall exactly what the problem was), and the water jackets were also different. The 7120 has been the basis for several writeups, and requires the least amount of work for the swap.

Just my .02,

Ted

87 YJ, AX15, NP231, Mopar MPI, 3.5 BDS, MORE Shackles, Posi-Lock4x4 front D30, Dana 44 Rear, 3.54, 32x11.5 BFG KOs, 4wdhw rear swing carrier, TrailMax Pro seats.
98 Grand Cherokee Laredo SE.
 
G

·
Discussion Starter · #18 ·
Ted, you'll notice a very nice difference in performance if you still do the head swap with your Mopar kit!
The reason for using the 7120 cast head and not the other one is that only the 7120 is the High Output head. The other is just a regular 4.0 head that is very similar to the crapy 4.2 head we are trying to replace. The whole point here is the HO.
The most common way to plug the water jackets is to use a "liquid weld" or "liquid steel" type epoxy product. The head gasket actually covers these jackets so any type of sealer for them is just extra insurance anyhow.


'88 Sahara, 4.2 that runs thanx to every Cheap trick on this board. The rest is getting there!/wwwthreads_images/icons/blush.gif
 
G

·
Discussion Starter · #19 ·
ok, i just searched my '97 head and found
neither #s.

when in doubt.........
empty the magazine.
 
1 - 19 of 19 Posts
Top