Pros and Cons of 258

[shadow1991]

Just wondering if a 258 can be built to be a good replacement for a 360. Why not keep the 360? MPGS, just considering different options. Any advice or insight would be great, thanks!!!

[Chumley360]

From my dealings with the 258 it's not really an "economy" motor. It's a great motor, I love them to death, but it's not where I'd turn looking for more MPG's. It's been discussed on the forum and I believe the general consensus is a diesel swap is the best bang for the buck. Now a diesel, OD trans, and a lower set of gears is probably the winning combo overall.

But back to your question; yes a 258 could be built as a good, reliable 360 replacement. But the cost of doing so might be better spend in a different swap, IMHO.

[joe]

Good reliable torquey grunt motor. Doesn't like high RPMs, so don't spend a bunch of money trying to make it go fast. Not a high mpg motor either. If your rig had one I keep it before swapping to a V8 but going from a 360 to 258 ain't worth the swap grief. If you're looking for mpgs:
A: you bought the wrong vehicle.
B: go diesel.
C: save the swap costs and put the money in the fuel tank.
D: if money is a big concern rethink "A."

[tgreese]

IMO you're better off with a 4.0L HO than a 258. The 258's problem, as mentioned, is that it has a long stroke compared to its bore. The stroke ratio is a central factor in where the torque peaks for any given engine A long stroke engine (undersquare) will have a lower RPM torque peak than a short stroke engine (oversquare) of the same displacement. HP is basically torque times RPM, so the higher the torque peak, the more power, all other factors being equal.

The 4.0L (242) engine has a larger bore and a shorter stroke, and makes significantly more power than the 258 (4.2L). More power is better at highway speeds, but you lose much of the low-speed acceleration that people like about the 258.

The 4.0L HO also comes with the excellent Mopar multiport fuel injection, and will give you better fuel economy than the 258.

[trailscape]

This is where I'm presently torn. My 258 is too loud and obnoxious for a six, gets about 4mpg and could probably use an overhaul. That said, on the occasional day the weather is right and the planets align that little 258 can burn rubber and run so nice it'll leave me grinning.

I'm either going to give in and pay someone to fix my carb or swap in a complete 4.0 setup. I'd love a 360 but that seems like a whole lot more work.

[mdill]

Upside Jeep used the basic unit until a couple years ago.
Easy swap to 4.0 or build a 4.5-4.7 stroker, drop it in the same hole as the 258. (Will spank a stock 360)

Downside of keeping a 258 (?) I like them a lot, simple to keep going, not much grunt but will pull down in the RPM range pretty good.

Swapping on it for a FSJ that had a 360 ? Way not worth it, Jeep did to many things different between the V8 rigs and the I6 rigs to do that without a organ donor right next to where you are doing the swap.

[Tornado230]

http://www.cliffordperformance.net/

Let your wallet be your guide.

Also---http://jeep4.0performance.4mg.com/index.html

[Metal Twister]

Could of had a V-8. Had them both and there is no comparing them. Enjoy your new V-8.

[CJ5]

Mileage wise they are pretty equal. The I6's I own get better mileage than the 360's I won.

The I6's are quick and have plenty of torque but the 360 is a bit better.

They are both easy to work with and are dependable.

The I6 is the most durable/reliable motor ever built. The 360 certainly has advantages but in the long run you are not going to beat the durability of the I6.

This is from experience. I have owned 6 I6 Jeeps and all of them had in excess of 350k on them with no major work. In fact, I have given them away to family and friends and all 6 are still going. I have 2 new Grands with I6's. I never even considered anything else when I purchased them.

[jeepjerry]

258s are great engines, but it wouldnt be worth all the trouble to change over from a 360 to one. I would shoot for a 4.0 first like mentioned above.

They do get decent fuel mileage though. My old '83 cherokee pioneer averaged 17-18 mpg and i had a '84 amc eagle that did 21-22 mpg. Took much less for the 258 to move a mid sized car compared to a full size jeep though. They were both manual transmission vehicles.

[jeepcomj]

pros....

crank and rods are good to make a stroker out of a 4.0

cons...
everything.

[GaJeep94YJ]

since you are in SC, I got a spare 4.0HO from a 98 TJ sitting in the garage I can make you a good deal on!

[mud89]

Another option if you already have a 258 : a 258 with the 4.0L head
You still have the low rpm torque of the 258, and you have more power at high rpm thanks to the 4.0L head
Not sure that you have a better mpg than the stock 258 ? I guess so if you get the injection with the 4.0L head

[drlocke]

I've always thought an inline 6 was a good motor. If my Wagoneer had one it would still have it. It came to me with the V8 and it still has it. I think joe summed it up pretty well with his ABCD stuff.

Around the farm I think a 258 would probably be fine in a Wagoneer/Cherokee. But mine is apt to be there, and also driving in the population corridor of the Northeast and vying with traffic that tends to run up one's backside if one even thinks about driving as slow as the speed limit. I can't help but think that a 258 would have to work pretty hard to do what the 8 under my hood seems to do without half trying. This is more than mere speculation, because I have driven all types of vehicle with both types of motor. When Kaiser started phasing the V8s into the SJ line they did so for a reason.

You may get a couple more MPGs out of the inline 6, but I doubt it would be worth it in the long haul. No matter how much prices go up at the pump there will always still be more to the equation than MPG alone.

[smogdredd]

The brick factor

All SUVs and pickups suffer from the brick factor. This limit puts You at a maximum MPG of 17-20 under ideal conditions. Ideal conditions are steady state highway cruising. Unfortunatly the only room for improvement is precise fuel controll and discopline of the right foot. Even in a 3/4 ton Ford with a fuel injected 460 17 mpg is not ony possible but relativly easy to acheive. Deisels are slightly better at around 19-22. The simple fact is that Newtonian physics are not just a good idea, it's the law. If You want gas milage weight and areodynamics are the only answer, That's why all the cars look like a squashed potato!