Axle gearing for 4.0 swap?

[jaber]

I got a 4.0, with auto tranny and NP231 t-case to put into the '51 Willys wagon and wanted to know what gearing came with this set-up? The doner has 2.72 at the moment and I have 3.54s readily available, just wondered which is closest.

Thanks in advance...

[Jeepguy77]

IIRC our 91 comanche with the 4.0 and 5speed has either 3.31s or 3.73s, so 3.54 should be right in the middle. Yes those gears should work just fine.

[Cecil14]

3 or 4 speed auto? The YJs with that setup usually got like 3.08s or 3.55s. Not sure what the XJs ran. For reference, I'm running a 4.0L/NV3550/D300 in my J-10 with 3.54s and 32s (actual measurement about 30.5). It weighs in about 4300#. Plenty of power for cruising right now, though it's certainly no speed demon. It will cruise at 70mph in 5th gear on most hills, have to downshift for some of the really big ones.


aa

[Chevelleguy]

XJ with an over drive ran 3.55's.

[1983 j10]

i have a 93 xj with the same set up it has 3.55s in it so 3.54 would be just fine.

[ComancheRob]

If it came with a 4.0 underhood with an auto behind it, 3.55's.
If it came 4.0 underhood and a 5spd behind it, it has 3.07's.

General XJ/MJ rule.

4cyl 4spd got 3.55's, 4cyl 5spd got 4.10's.

This is ONLY '87 +

84-86 are whacky years.

[Chumley360]

I just got done crunching these numbers 3.54 gear with 32" tires will get you about 1800 RPMs at 65 MPH (this is an estimate as I don't have the numbers in front of me). So it'll all depend on your tire size. I was looking at running 3.73 with the 32" tires and that will get me closer to the stock 2k RPMs at 65 MPH.


Sorry I only skimmed the post. Most(biased on internet research) 4.0L/AW4 4wd XJs seemed to have 3.54 gear OE. Some had 3.73 and a lot of the 4cyl had 4.10. They also mostly came on 235/75-r15 tires so that's what I biased my numbers off of.

[jaber]

I got the motor, auto(overdrive, I think), and t-case from a '90 Cherokee. Its an MPFI and I need to find a computer and harness to try to figure it out.

I'm using an '85 GW frame and both axles. I think it will be a nice setup. I will start a build thread when I get going. Just trying to get all the parts located.

Thanks guys, thats great news....

[1983 j10]

i have one form a 93 with the same set up i am selling just let me know if your interested i also have many other parts form the same rig. also your trans is an aw4 auto its a 3spd with overdirve. and that should be the high output 4.0 its a better fuel system then the pre 90's.

[jaber]

I'm interested, send me a PM with price or trade. Thanks.

[1983 j10]

pm sent

[ComancheRob]

Acctually boys, Jaber's 4.0 and your 4.0 are NOT the same.

Jaber, your 4.0 is still of RENIX flavour. Non-Ho. 91-95 were the Chrysler High-Output motors. You'll need the entire harness from the donor XJ PLUS the motor if you plan on doing an HO 4.0 swap.

Or stick with the 4.0 you've got and find a RENIX harness and Tranny Harness.

[Cecil14]

Acctually boys, Jaber's 4.0 and your 4.0 are NOT the same.

Jaber, your 4.0 is still of RENIX flavour. Non-Ho. 91-95 were the Chrysler High-Output motors. You'll need the entire harness from the donor XJ PLUS the motor if you plan on doing an HO 4.0 swap.

Or stick with the 4.0 you've got and find a RENIX harness and Tranny Harness.
To tell which you've got count your throttle body screws. Renix engines have 3 screws holding the TB to the intake, Chryo HO engines have 4 screws. If you have a Renix engine now but no engine management then I recommend getting the pieces you need to convert over to the HO setup. The wiring is actually REALLY simple...I JUST finished mine and can help out if you've got questions.

To convert a Renix engine you'll need the following from a Chryo HO engine ('91-95 systems are the easiest to implant):

Head
Intake
Valve Cover's are the same I think...think mine is actually off a Renix engine...
Throttle Body
Injector Rail (I like the rail with the regulator up there) and Injectors
Wiring/Computer
Either a bellhousing with a CPS boss or a relocator kit to put it on the balancer. Hesco makes a kit, not sure if anyone else does or not. If you've got an XJ transmissions you've probably already got the boss in the bellhousing.

I'm not sure what the fuel pressure requirements are for the Renix system? I know the HO system requires about 45-50psi. I'm running a 'burb tank and using the burb's intank pump. Haven't driven it yet, but from a couple test runs so far it looks to be good. Fuel pressure is right where it should be, and the regulator is doing it's job as well.


aa

[1983 j10]

does he really need the head as well or just the intake with the ho injection. i dont think they changed the head when they went to the ho system. i actually have an 88 head and the ho intake and exhaust manifold bolt up to it just fine.

[Cecil14]

They moved the intake ports up on the HO system. That's not to say that the newer intake won't bolt onto an older head, I don't know there, never tried it.


aa

[1983 j10]

ok so unless he gets a ho head what i have wont help him any.

[jaber]

Wow.
Thanks for all the information. I might check the yards here and see what I find. I will keep you in mind, 1983 j10. I still have some time till I'll get to that stage, but I will get there. The shipping on something like that would be high I'm sure. Money's real tight at this moment.

[1983 j10]

yea a head would be a lot to ship i think the weight on one is close to 60 pounds and its like 3 feet long.

[jaber]

Got confirmation today from a baby Jeep site that the intake would not be an upgrade without the head. Let me talk to a few friends about a head....

[Casey]

If it came with a 4.0 underhood with an auto behind it, 3.55's.
If it came 4.0 underhood and a 5spd behind it, it has 3.07's.

General XJ/MJ rule.

4cyl 4spd got 3.55's, 4cyl 5spd got 4.10's.

This is ONLY '87 +

84-86 are whacky years.
Yep my '86 MJ has a 4cyl, 5spd and 3.73 gears. ;)

I'm sticking with the 3.54 gears that my '74 (ex-258/TH400) powered Cherokee has. I will be running the XJ 4.0/AW4 so I know it will work well with 31" tires. I've had half a dozen XJs set up that way.