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I am looking at used jeeps and I will be a first time jeep owner. I am interested in CJs or YJs. I want the jeep mostly for hunting and putt-ing around town. As far as engines go, do you think a 4 cyl would be okay for what I want and not get me in trouble in the mountains, or should I just look at the 6 or an 8 cyl? If a 4 would work, what transmission, axle gearing and tire size would you recommend? I have already found the forums to very informative. Thanks.



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Hi, Rich…Although I'll always be a CJ buff, I’d suggest a YJ Wrangler.  If a six-cylinder, go with a 4.0L inline, 1991-up model.  For four-cylinders, the 2.5L is TBI from ’87-’90, multi-point FI from 1991 to 1995.  Four-cylinder models tend to be less expensive.  You’d have to be sold on the idea, however. 


If not, the conversion to a six-cylinder requires welding engine mounts and an upgrade of the transmission as well.  (See my MIG welding article with illustrations of this conversion in a YJ Wrangler; the same applies to the TJ Wrangler, as each uses a different frame for four- versus six-cylinder engines.)  The six-cylinder YJ Wrangler models use a Peugeot ('87-'89) or Aisin AX15 ('89-'95) transmission; four-cylinder models use the Aisin AX5 (lighter duty).


I’m okay with the 2.5L four-cylinder for off-road use.  In low range, the four works fine off-pavement if the axle gearing is 4.10 (stock) and tires are stock diameter.  If you do a lift kit and oversized tires to 33”, you will need 4.56 gears to move a 4-cylinder Wrangler down the road.  For each of these reasons, you may be happier with a 1991-95 factory 4.0L six-cylinder model in decent shape. 


Avoid the '87-'90 4.2L/258 inline six unless you want to restore the carburetion (see my article) or upgrade the induction system to EFI.  (This EFI article on MSD Atomic EFI also describes the Mopar MPI and Howell retrofits for the 4.2L inline six.)  Even with a six-cylinder model, tire diameter still dictates gearing.  Retrofit 4.56 and 4.88 ring-and-pinion sets, front and rear, would be practical for 33” and 35” tires, respectively.


Trust this helps.  If you do consider a CJ, and they are all carbureted, the 1980-86 would be the best year range, as they use the iron Dana 300 transfer case with helical gears.  Like the '87-'90 YJ Wrangler 4.2L, the emission-laden, carbureted 258 six can be a pain for some...I've restored these systems—it can be done.


An emission legal 258 EFI conversion package runs from $1400-$2800.  (Even the four-cylinder CJs are carbureted through these years.)  That’s enough to say, “Pass.”  This is now older technology, and nostalgia only plays so far:  You get the restoration bills.  I would not consider a 1975 or older CJ, unless you want to fully restore a vintage Jeep and have the time and money to do so.


Arguably, the later CJ’s Dana 300 transfer case is superior to the NP207 (earlier four-cylinder) and NP/NV231 (later four- and six-cylinder YJ models).  Despite that, an NP/NV231 will last plenty long and is typically less costly to rebuild.  The light duty NP207 can be another story.


Trust this helps, Rich…Happy to carry the conversation further—Welcome to the 4WD Mechanix Magazine 'Tech and Travel' Forums, looking forward to your topic posts!



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What's up Rich?


  I will not be as detailed with my reply as Moses is, but I will back him on Jeep suggestions. For a first time Jeep the 91-95 YJ is hard to beat. I suggest going with the 91 or newer so you can have the fuel injection. It is much easier to off-road with fuel injection and trouble shooting it is really simple given modern electronics.


  I have nothing against the CJ or TJ, I just think your money goes further with a YJ. The YJ is still a leaf spring system witch makes things pretty simple to work with. A 4" lift kit is less than 500$ (should you plan to modify this way)


  I suggest getting the 4.0 inline six engine. That is the one thing I wouldn't budge on. It's expensive to add power later. The 4.0 is really the perfect match for the YJ. Not too much power that you break things and powerful enough to get the job done.


As for the transmission.. I like automatics but every Jeep I ever owned had a manual. The manuals are easier to work on in my opinion but I cant see the fault either way. That's on you. If you off road a lot you will wish it had an automatic, especially after a good day of feathering the clutch up some rocks lol.


  The only advantage I have ever seen with the 4 cylinder Jeep (besides price) was in the axles themselves. They have (maybe not all) a 4.10 gear package from the factory to compensate for the engine's lower power range. This 4.10 gear sits on a bigger carrier. We used to take these axle assemblies and put them in our 6 cylinder jeeps and get the 4.56 or 4.88 gear sets with a track locker so we could run 35" tires. I have built a couple this way and as long as you finesse the trails you won't  break things.


 As for your tire size, that really depends on your terrain. Most would have you believe the largest tire you can possible fit in the fender well but I say match it to your riding terrain. If your not climbing 4' ledges I don't think you need 46" tires. Plus it all comes down to the axle modifications and gearing. If you're going to stay stock then I wouldn't go past a 33". this will keep your center of gravity lower and maintain a better gear ratio for fuel economy.


  The factory transfer case (NP231) and axles (Dana 30 & 35) really aren't that bad if you don't abuse them. I ran 35" tires with lockers for many years and the only thing I ever broke was a u-joint. And that was due to incorrect driveline angle. You can modify the factory T-case with a Terra low kit (assuming they are still in business) and regain some strength and lower gearing (4:1 reduction on low). In the end I have gone over the same trails that broke Dana 60's with my Dana 30/35's and barely scratched my diff covers. Its all about the driver. If you're hard on parts then you need parts that are harder.


   Also, the aftermarket world for the Jeep YJ is huge. There is nothing you cant get for this vehicle in OEM or full custom.


  Hope you get your Jeep and maybe will see you on a trail someday.

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Thanks for adding so much filler detail from your experience, Megatron!  Rich now has a wealth of information.  I back up everything you share here.


4.0L EFI is a must, the BBD carburetor on the 4.2L CJs and '87-'90 YJ drives an entire aftermarket in EFI conversions that cost an ample sum. And like you share, there's not that much mystery and no threat in electronic fuel and spark management these days.


You're absolutely right about the 4.0L inline six conversion.  At the magazine, I feature the welding and fit involved in converting a 2.5L YJ into a 4.0L.  After the Jeep CJ era, AMC/Jeep and Chrysler decided to make unique frames for inline four- and six-cylinder engine applications.  On AMC/Jeep CJ's, the V-8s, fours and inline sixes simply required different, bolt-in frame adapters.  Actual frames were identical...


Installing an inline six in place of a YJ or TJ Wrangler's four-cylinder engine is no less complex than a V-8 conversion—see the Advance Adapters 'LS' Chevy V-8 into a Wrangler.  Four-cylinder YJ models make good candidates for a V-8, although the four-cylinder YJ's AX5 transmission does not meet the torque rating of an AX15.  A V-8 into a four-cylinder chassis begs the use of a 4L60E or 700R4 automatic.  Advance Adapters is your source for the conversion parts.


Transmission wise, the YJ has the 904/999 Chrysler three-speed automatic without overdrive. The '91-'95 features an AX15 manual transmission behind the 4.0L inline six.  It's a proven transmission that I detail in the 209-step, two part how-to rebuild article at the magazine.


Good point about the axle housings for the lower (numerically higher) gears. This is a well taken point for those wanting 4.56 or 4.88 gears in their YJ Wrangler. These larger ring gears will only fit Dana 30 axles designed for OEM 3.73 or 4.10 gear sets and Dana 35 axles with 3.55, 3.73 and 4.11 OEM gears.  (Yes, they did use a 4.10 front with a 4.11 rear axle.  This is common for many 4x4s and has to do with axle design or, in some cases, the use of two manufacturers.  These YJs all use Dana axles.)  The YJ Wrangler featured at the magazine's tech how-to was originally a 2.5L TBI with the lower gear ratios that Megatron describes.


Great description of tire needs.  The YJ Wrangler project at the magazine is my son-in-law's '87 that I built up—lucky him, eh?  We stayed with the 30 front and 35 rear, ARB Air Lockers at each end with Superior Axle shafts for "Super" status; 33" tires, 4.56:1 gears, and he's gone all over Moab and elsewhere. 


Think of it this way:  Sure, both the Dana 35 and 30 are small, but when you're off-roading, the 231 transfer case delivers 50/50 torque split to the axles.  The Dana 35 rear only needs to tolerate 1/2 the torque it gets when the Jeep is on the highway in 2WD high range!  So, these axles will work as long as the axle tubes remain straight...An axle truss can help here.


Megatron is right about the NP231, too.  Durable for a chain drive transfer case, hardly a weak point!  I cover the NP/NV231 transfer case rebuild and SYE kit install at the magazine if you want details on what we're talking about here.  A reduction gear set for this transfer case can take low range down a notch for those oversized tires.  Then there's the Atlas transfer case—the ultimate transfer case solution.  For a stock 4.0L inline six, the NP231, in good condition, will last indefinitely.  Parts are readily available for rebuilding.


Megatron is pragmatic and right: The Dana 60 monster axle housings hang so low that any real ground clearance gain requires 40" diameter tires to accomplish!  Megatron's 35" tires with a Dana 35 or 30 axle makes perfect sense for useful ground clearance.  Strange how these 60s got beneath Wranglers and CJs in the first place.  An AMC Model 20 or Dana 44 axle is more than enough.  60s are a lot of unsprung weight mass and very costly to build and adapt.


Thanks, Megatron, you've sparked interest and inspired others to jump into this discussion!



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