258 swap question New guy here

[trap1968]

Hello everyone. I am new on the site. I just bought an 89 Grand
Wagoneer that I am restoring for a daily driver because it has always been my favorite vehicle. My father owned and 87 and I had an 86 in the past and loved it but it was rough....very rough. I have a new 360 to put in it but am considering a 258 for fuel mileage. Motor mounts obviously are a concern but what can I expect to be problematic when if I do this swap as far as vacuum lines, transmission, etc. I probably wont be going off road much in this one. (I am buying a CJ later for that) The heaviest thing I will pull is a 19 or 20 foot boat.

Thanks for all of your help and I look forward to reading this site. It looks great so far.

Troy

[Cherokee-Kid]

Hey trap....welcome and congrats on the new to you Grand.

Well it has been discussed before about fuel mileage with an I6 vs. a V8. It seems that the opinion is that there is no major benefit in fuel economy with the six.

In your case of conversion it is definetly not worth the effort, in my opinion. There are clearence differences in the firewall of vehicles with the six as well as radiator support differences. The 258s are a longer engine and need more front to back room. You would be much happier to update to a fuel injection system than to decrease power without decreasing much in weight (if any) and all on top of the fitment issues.

I'd consider building a hot little 304 before converting to an I6 but then why when you have a 360 ready to go?

[jeepjerry]

Yes, i agree, it would be major work to put a 258 in your wagoneer. You will need to move the trans back and get the correct driveshafts also. I was also thinking a nice 304 would be a good move, use a rv/tow cam that can also benefit fuel mileage along with a small cfm four barrel, you would be able to tow what you need and get decent fuel mileage when you arent towing.

I have a 304 in mine, and i tow a car trailer with my off-roader cj-5 on it. I get mid teens for fuel mileage but i am a bit rich at the moment and need a smaller carb.

[tgreese]

Regardless of what you do, you can't squeeze blood from a stone. Mostly you will get mileage proportional to the power needed to propel the car, not in proportion to the engine displacement. Fuel in is proportional to power out.

Search for discussion about putting the 4.0L HO inline 6 in the Wagoneer. As much as I like the 258, the 4.0L clearly has the edge in economy and highway power. You'll want to keep the Mopar multiport fuel injection that comes with the 4.0L HO engine.

[Serious Johnson]

Troy:

For once, I'm pretty much in the same camp as evertone else here. Most Grand Wagoneer owners towing anything at all with a 360 with automatic transmission feel a need for more power on much of a slope at all. A smaller engine will return better economy at full-throttle in top gear, and somewhat at light load. But asking a lower power engine to move such a massive hunk of metal will have the slushbox tranny down in the lower gears much of the time. The longer you stay in the lower gears, the more fuel you'll burn. I'd think that the only way you'd see much, if any, fuel mileage benefit with the I-6 is if you also switch to a manual transmission so that you can lug it when appropriate. Heck, you'd probably get most of it with the transmission even behind the 360.

That said, I've been halfway considering swapping my hotrod 360 for a 4.0 and turbocharging it.

S.J.

[jeepguzzi]

Originally Posted by Cherokee-Kid

Hey trap....welcome and congrats on the new to you Grand.

In your case of conversion it is definetly not worth the effort, in my opinion. There are clearence differences in the firewall of vehicles with the six as well as radiator support differences. The 258s are a longer engine and need more front to back room.

Not exactly. The 258 is a longer engine, but there are no differences in the firewall. The 360 actually sits further forward than the 258. That is why there are radiator support differences, they cut a chunk out of it for the 360. The width is not the problem, I went from a 258 to a 360 and used a 3 core 258 radiator mounted to 360 radiator brackets and cut the chunk out of the support. The difference is in the engine mount support towers on the frame.

[addicted]

It is not as easy as it seems. As you know the fram mounts for the engine are different and bolted to a seperate set of holes along with welded to the top of the frame. The trans will need to be moved back to the farthest set of holes on the frame. Altered drive shafts. You will also need a different torque converter. If you go with a 4.0 or even a 258 with 4.0 head you will need to hydroboost the brake system for clearance of the intake. Vacuum hoses and such shouldn't be much of a problem but getting down the road in a head wind or up hill will not be great with the power draining 727. After all that work and time your mileage will not be a whole lot better if you keep the auto and don't change the gears.

So my suggestion is if you are going to do it you should change the trans to a manual or at least try and source an auto with a locking torque converter or do what I am doing and swap an entire XJ powertrain into it so the parts work well together because they were designed that way. I am figuring high teens on the highway and mid teens around town with a 4.0/AW4/NP242 and 3.73 gears. I plan on towing some with it but 3.54's would probably be perfect for something mainly used as a commuter and no towing since most XJ's came with 3.55's.

[Bill Moore]

Originally Posted by addicted

It is not as easy as it seems. As you know the fram mounts for the engine are different and bolted to a seperate set of holes along with welded to the top of the frame. The trans will need to be moved back to the farthest set of holes on the frame. Altered drive shafts. You will also need a different torque converter. If you go with a 4.0 or even a 258 with 4.0 head you will need to hydroboost the brake system for clearance of the intake. Vacuum hoses and such shouldn't be much of a problem but getting down the road in a head wind or up hill will not be great with the power draining 727. After all that work and time your mileage will not be a whole lot better if you keep the auto and don't change the gears.

So my suggestion is if you are going to do it you should change the trans to a manual or at least try and source an auto with a locking torque converter or do what I am doing and swap an entire XJ powertrain into it so the parts work well together because they were designed that way. I am figuring high teens on the highway and mid teens around town with a 4.0/AW4/NP242 and 3.73 gears. I plan on towing some with it but 3.54's would probably be perfect for something mainly used as a commuter and no towing since most XJ's came with 3.55's.

I agree, A manual is the only way to go behind the 258, also a 5 speed like a nv3550 or ax15, he also has 3.31 or 2.73 gears. A properly tuned I6 should get you close to 20 on the highway with a 5 speed, but it will not be a powerhouse, sufficient maybe, but no reserve. The 83s came optional with a T5 and I6 from the factory, but are hard to find. I havent seen one since I had one in the 80s. An xj swap of a 4.0, ax15 5 speed would be the best

[trap1968]

I really appreciate all of your responses. No matter what the mileage I love my (second) Wagoneer.

After reading for hours on this site I may do the Pro-Jection system.

Honestly, is there an increase in mpg by doing this?

If I don't do it now I probably wont. I have been saving for a 2009 F-150 and when it came down to it I chose an 89 Wagoneer with the engine on a stand!!!! I am using this money for the entire refurb. which means I will have the same amount of $ in my Wagoneer as my down payment was going to be. Not bad... Saved money but still want a little better fuel economy....

We are working on the engine bay now and I really need to make a decision on the fuel delivery.

Thanks,

Troy

[tgreese]

Do you need a turnkey EFI solution? You can hack together fuel injection for a few hundred dollars using junkyard parts and either a hacked factory ECU or a Megasquirt. This is something that can be done at any time.

If you want to change the drive train, now is the time to do it. Otherwise I would advise you get everything put together and running, and then try to squeeze out a few more MPG from the stock configuration. Major changes will be expensive, and unless you plan to put a lot of miles on this car in the next few years, you will not make back your investment.

Another possibility, if you have the time, is to step back from the car and do your homework. Consider your own skills, the amount of time and money you have to dedicate to this project, the cost and return of any changes, and work the numbers. Sorry if this sounds negative, but fuel economy is a topic that's been discussed over and over here... there's plenty of information online already.

[Stuka]

I used to get 17-18mpg all day long in my J10 when it was stock (slightly modded 258, T176, 2.73's, 31's). Now I get well... worse heh. Best my cherokee ever got (slightly modded 360, T18a, 3.54's, 31's) was 14.5 average.

But as said, its quite a bit of work to swap over. If you really want better mileage, look into diesel swaps. It cost more up front, but with the right setup, you can get into the low to mid 20's.

[billyrb]

for towing and time / money / etc., you'd be better off using the 360 and converting to a 700r4 Overdrive transmission. You'd get better mileage PLUS have all the power of the V8, without hardly any work.

[budojeepr]

Originally Posted by billyrb

for towing and time / money / etc., you'd be better off using the 360 and converting to a 700r4 Overdrive transmission. You'd get better mileage PLUS have all the power of the V8, without hardly any work.

I agree. I don't know what's involved with adapting the 700R4 to the 258, but a 4-speed with lockup torque converter would be nice.

I had a 258 with Pro-Jection in my Wagoneer, and got between 12 and 15 mpg; highway or city, it didn't matter.