• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

4.0 intake on a 4.2 head?

Gerr

NAXJA Forum User
anyone know if its a simple bolt on swap or more complicated or impossible without major mods?

I remember reading once hesco makes a aftermarket head for the 4.2 and 4.0 and it was the same head so what im wondering is if I can take my 89 yj with crappy carb and swap in my 95 or 93 parts heeps intakes to get a fuel injection setup.
 
What are you crazy? Swap the whole 4.0 head! If you have two of them laying around! :) Then run the 4.0 head until to have one of the other 4.0's pulled out of your parts heep, rebuild it and swap it in for that ever loving POS 4.2

Not tying to be insulting, I had the 258 in my YJ and it sucked up well over a grand (Hesco cam, Holley Projection, Header, 4.0 HO head conversion etc.) before I realized that the 4.2 is one seriously un polishable turd.

Save your self a lot of time and money and pull the 4.2 for it's crank and rods and swap them into one of your 4.0's to make a 4.6L stroker:
http://www.angelfire.com/my/fan/stroker.html

It's easier and in the long run it will be CHEAPER than trying to make any serious power with the old 4.2.:smoker:

Anyway to answer the actual question, yeah, you'll have to drill out the holes for the alignment dowels, the old 4.2 head's dowels will hit almost EXACTLY one dowel width above the 4.0 intakes existing dowel holes. ... I know this because I had to lightly grind two tiny half moons just under the existing holes of my 4.2's Intake to fit onto a 4.0 head, when I did the 4.0 head swap on my YJ's 4.2. The grinding JUST missed breaking through to the bottom of the stock alignment hole. The reverse would thus be true of a 4.0 intake to the 4.2.

I'll try to throw some pics of this up tomorrow at some point.
 
Last edited:
A full head swap is probably what ill do but Im not wasting a good 4.0 block in a heep I dont think I will keep. And really with the 4to1 in the t-case powere has never been a problem but hard starting and carb flooding has
 
BLSXJ said:
on a side note does any one know if a 4.2L intake will work on a 4.0L HO head?
no it wont, the 4.2 head is narrower.

the 4.0 HO head will fit on the 4.2 but it will require you to jb weld the water jackets on the head since it over hangs a little bit. i bored a 4.2 and swapped it into my xj with a 4.0 HO injection and it seems to do well, no where near the power of a 4.6 but still has enough torque and grunt to take care of me.
 
BLSXJ said:
on a side note does any one know if a 4.2L intake will work on a 4.0L HO head?

I just got done describing just that! Not trying to be rude or nothing but:
"I had to lightly grind two tiny half moons just under the existing holes of my 4.2's Intake to fit onto a 4.0 head, when I did the 4.0 head swap on my YJ's 4.2"

For the other guy, it does fit. it';s not plug and play but the 4.2 carb style intake fits on any 4.0 head. Just requires a bit of grinding below the alignment dowl holes as described above to make new holes and slightly larger washers to grab the "ears" on the 4.2 intake, and you just KNOW the existing brackets need to be reworked. will post pics after lunch
 
the reason I ask is I'm looking in to installing a 91 4.0L based stroker in to an older jeep or possibly a buggy. So I'm trying to figur out the best way for the motor to be a "stand alone" so it will either be running on a truck avenger carb and MSD ignition or a hacked togther wiring harness out of a jeep.
 
These are thumbnails click for the larger version.
before shot typical carbed YJ (88) with nightmarish non operating emissions garbage and infamous carter BBD the shittiest carb ever:


4.0 head and cheap chinese ebay header that is STAINLESS STEEL and cost 44 bucks SHIPPED at the time... the steel would cost more than that here (this header held up for a couple years and outlasted the 4.2 pictured)


Had to clearance the intake to fit the header, others have dented the header pipe to fit the intake, but my intake was no longer in need of it's coolant passages or the stock "heater" used to warm things up for the crap carb on cold starts. I put in Holley TBI injection and eliminated the heater return line plumbing to improve air density:


Initial test fit the 4.0 gasket fit well outside the edge of the intake runner ports on both the 4.0 head and the 4.2 intake, marking things and lining them up carefully proved to me that the 4.2 Carb intake has LARGER runners than the head by maybe a 32th of an inch all the way around the port. Slight loss of velocity perhaps, but nothing to worry about:


Needed to clearance this bracket, later I would weld new tabs onto another bracket and swap it in, but the intake was very secure even without it, I at one point acidentally put all my weight on the intake torquing down those damn rear valve cover bolts, it stayed put.


Here's the final product, for some reason I got goofy and gave the header a mild polishing... I have an unhealthy facination with Stainless steel... It started with a 65 fastback Mustang in 1988 and grew with an 88 YJ and 91 XJ They are all extremely rust prone and so started my facination with SS even my wedding ring had stainless steel protecting the gold band. call me nutty. anyway:


HTH:smoker:
 
Back
Top