258/4.0 Vs. TBI 350 Chev, School Me

MrBeast

Explorer
So on my 80 CJ7 the transmission is Kaput, shot, and needs to be replaced. The Dana 300 is in decent condition, but could use a good going through and cleaning up.

I have decided that I am going to use one of the NV4500's that I have in the Jeep, but where I am stuck is figuring out what I am going to do for the motor in the long term.

Currently the Jeep has the original 258, it runs strong, sounds good, leaks a bunch of oil out of the pan, rear main and valve cover, but it it is certainly not beyond repair.

My options are when I drop the transmission I can either clean up the 258, install a new pan gasket and rear main and valve cover, and continue to run it until I can rebuild it with a 4.0 head, EFI and some other goodies, in fact I can get a complete 4.0 with a bottom end knock but good head for 200 bucks. I was even thinking about doing a stroker with a cam.

My other option is I have a Chevy 350 that came out of an 89 suburban that runs like a top. It is a little ugly on the outside because it has been in some salt, but it will clean up just fine. I have the throttle body, all of the accessory drive and goodies for it, id just have to drop it in.

Either way I go I will have to buy a bell housing because I don't have one.

I am really wondering which is going to be my best bet for the long haul.

I know the I-6 should get decent fuel mileage running the 33 11.50's and 4.10 gears, I will be at 2134 RPM @ 70MPH, 1981 @ 65MPH.

The jeep is going to be a daily driver that will see regular trail use, I am going to be driving it to Alaska in the spring, and it will be my primary mode of transportation when I move there.

I would really like to know what those of you who have done similar swaps think, what you liked and what you did not like.
 

Eaglefreek

Eagleless
I don't have any experience with a V8 in a CJ7 but I have a 258 with a 4.0 head and while it is a big improvement it's no V8. I would guess the 350 would get close if not better MPG than the I6. I know 2 guys who both had strokers one in a YJ and the other in an XJ. They weren't satisfied with the stroker and later went with V8's. One an AMC 360 and the other a 5.3L Chevy. They are both happy with the V8's.
 

reece146

Automotive Artist
Where are you located?

Do you already have the adapter for the NV4500 to the AMC engine?

If it were me and I was not concerned with trying to keep power at altitude I would get a drivetrain out of a TJ or XJ and build a 4.5 "poor man stroker" using the 258's crank. That would be plenty of engine for a SWB Universal. If the cost of the adapter is an issue then use the AX15 or AW4 from the donor. The Dana 300 will bolt up to these transmissions... might need a spacer... research the details as I forget them.

The 350 would be decent but if you can avoid adapters you might be better off. A 350 bolted to your NV4500 bolted to a passenger side drop NV241 out of a Suburban might work nicely.

What vintage is the 350? Is it a "good one" or any economy target turd?

Around here you can pull a full "modern" drivetrain (XJ) from a yard for a few hundred bucks.

There are so many options... perhaps giving us some background on how and where you want use the Jeep would help. A simple to repair Jeep is a good Jeep to own. If it is too custom it can get annoying when things go wrong.
 

MrBeast

Explorer
Where are you located?

Do you already have the adapter for the NV4500 to the AMC engine?

If it were me and I was not concerned with trying to keep power at altitude I would get a drivetrain out of a TJ or XJ and build a 4.5 "poor man stroker" using the 258's crank. That would be plenty of engine for a SWB Universal. If the cost of the adapter is an issue then use the AX15 or AW4 from the donor. The Dana 300 will bolt up to these transmissions... might need a spacer... research the details as I forget them.

The 350 would be decent but if you can avoid adapters you might be better off. A 350 bolted to your NV4500 bolted to a passenger side drop NV241 out of a Suburban might work nicely.

What vintage is the 350? Is it a "good one" or any economy target turd?

Around here you can pull a full "modern" drivetrain (XJ) from a yard for a few hundred bucks.

There are so many options... perhaps giving us some background on how and where you want use the Jeep would help. A simple to repair Jeep is a good Jeep to own. If it is too custom it can get annoying when things go wrong.

I am in Corpus Christi Texas.

tonight it was decided for me, for all the running around since I bought the jeep it has used 12 gallons of gas, and I have been driving it quite a bit. Not sure how many miles that is, but it certainly has been quite a few.

I am considering simply rebuilding the 258 and putting a CNC ported Aluminum head on it with a good intake, and the Howell TBI setup that uses the V6 Chevy components.

I do not have the bellhousing to go from the Jeep engine to the NV4500, Advance adapters has it for 372.44 so not a big deal. Id be hard pressed to find the chevy bellhousing for half that. and then id have to do a hydraulic clutch conversion.

the 350 that I have is a 1990 L05 210 hp 300tq 4 bolt main out of a suburban.

I have also been looking around, there are a few late 90's XJ's around for 1200-1500.00, through the reading I have done though I have found that early 90's 4.0 heads have a cracking issue between #3 & 4.

That is why I am considering the aluminum head route, take and engine that I already know is in good shape, rebuild it with a new head, and add the EFI with a kit that uses commonly available parts that I am very familiar with troubleshooting, that has proven to be a very dependable setup. Although I will say the allure of using the Sequencial MPFI does have its charms, but with that comes complexity.

As far as the transfer case goes, I am going to rebuild and run the dana 300, Novak makes a input shaft and ring that bolt it to the NV4500.
 

reece146

Automotive Artist
It's not the early 90's heads that crack, it is the DIS (coil on rail) heads used in 2000-2001. I have been hit by this and used a Alabama Cylinder Head replacement head ($510) and it works great. Nice casting. If you use any other year XJ head you won't have this issue.

By Hescos site you can expect ~30 hp from the aluminum head. What you lose is about $2000 for the rest of the build and thermal tolerance if you have an overheat issue on a trail. If something happens and you lose your water pump drive or whatever you will likely cook or warp the aluminum head. Al heads are great for pavement pounders and sports cars, not a fan for trail rigs. Just IMO.

The reality is that if you are going to rebuild the engine anyway you would be better off to do a stroker for less money and be ahead of the game with respect to hp and more importantly torque.

If I was building it I'd likely go with a OBD-II head and EFI ('97-'01 if you use a cheap XJ donor), stroker formulas can be found here:

http://www.jeep4.0performance.4mg.com/stroker.html

As for EFI versus carb... you can't pay me enough to run a carb.
 

MrBeast

Explorer
with that head and a cam I am looking at the numbers on Desk Top Dyno,

Stock the 258 produces 112 hp @ 3200 RPM and 210 Ft/Lbs of Torque @ 2000.

Desk top dyno says by the numbers 246 HP @4000 and 331 Ft/Lbs for torque, the best thing about that is that it tells me the motor should make over 300 ft/lbs from 2000 to 4000 RPM. So it has a big flat wide torque curve.

@2000 RPM the engine produces 309 FT/lbs, with the 33x11.50R15's im going to be running, 4.10 gears, and the NV4500, the jeep will pull 1981 RPM @ 65mph, and 2134 @70, if I want to step it up to 75 and burn some fuel 2286 RPM, and 2439 to go 80mph, which I usually will drive 65 or 70, maybe 75 in the wide opens spaces out in Eastern Montana or the Dakotas.

The thing I like about going this route is that the jeep is actually going to lose about 30 lbs, because the aluminum head is lighter. as well the 350 I have is out of a 90 model suburban, it is a LO5 that made 210 hp and 300 FT/lbs of torque, in a rig that had a listed curb weight of 4450 lbs, vs the jeep that had a listed curb weight of 2707 lbs, granted mine will weigh a bit more with the winch and hard top, but if we call everything else equal and assume the jeep weighs in at 3100, it is still 1350 lbs lighter than the burban.

Seeing as how the I-6 is going to make more torque baseline than the 350 does at peak, and the same for horse power, so in theory with the setup I am going with, the engine should be a much better performer, and hopefully get much better fuel mileage.

The other advantage of the aluminum head is that the stock 4.0 head has a 3/16" deck thickness, where as the aluminum head has a 5/8" thick deck. Which means the head can be milled down for a true 10:1 compression ratio that because of the superior heat dissipation properties of aluminum can be run with out having to worry about detonation as long as I run premium gasoline.
 

MrBeast

Explorer
It's not the early 90's heads that crack, it is the DIS (coil on rail) heads used in 2000-2001. I have been hit by this and used a Alabama Cylinder Head replacement head ($510) and it works great. Nice casting. If you use any other year XJ head you won't have this issue.

By Hescos site you can expect ~30 hp from the aluminum head. What you lose is about $2000 for the rest of the build and thermal tolerance if you have an overheat issue on a trail. If something happens and you lose your water pump drive or whatever you will likely cook or warp the aluminum head. Al heads are great for pavement pounders and sports cars, not a fan for trail rigs. Just IMO.

The reality is that if you are going to rebuild the engine anyway you would be better off to do a stroker for less money and be ahead of the game with respect to hp and more importantly torque.

If I was building it I'd likely go with a OBD-II head and EFI ('97-'01 if you use a cheap XJ donor), stroker formulas can be found here:

http://www.jeep4.0performance.4mg.com/stroker.html

As for EFI versus carb... you can't pay me enough to run a carb.

I hear you on the carb, since I have moved over to EFI I have about forgot how to work on them, they aren't worth the trouble.

You definately have some good points there, I am going to do some more reading.

on the I-6 is a water pump failure common? I am coming from running all chevy V8's and I have never had one fail on the trail out of all of the stupid stuff I have broken over the years.
 

BigAl

Expedition Leader
I would not mess with swappin EFI onto a 258. The HO 4.0s are cheap and plentyful and produce more HP than the 258/EFI combo.
 

MrBeast

Explorer
I would not mess with swappin EFI onto a 258. The HO 4.0s are cheap and plentyful and produce more HP than the 258/EFI combo.

I am actually starting to look that direction, thinking about picking up a complete XJ for 12-1500 bucks in running condition, pulling the motor and efi, selling what other parts I can and scrapping the rest.
 

MrBeast

Explorer
I have been hunting around, I have been finding a lot of 97-99 Cherokees in the 900-2000.00 price range that would be good donors, found one for 1500 that has a 122,000 mile engine in it, manual trans, might be a great donor.
 

K2ZJ

Explorer
I have been hunting around, I have been finding a lot of 97-99 Cherokees in the 900-2000.00 price range that would be good donors, found one for 1500 that has a 122,000 mile engine in it, manual trans, might be a great donor.

Research the differences of the 99+. It has a modified head and intake for emissions reasons. The intake manifold is better but the head is restricted on the exhaust, still produce the 190hp.
 

reece146

Automotive Artist
on the I-6 is a water pump failure common? I am coming from running all chevy V8's and I have never had one fail on the trail out of all of the stupid stuff I have broken over the years.

Water pump failure is not an issue with these engines. I should have worded my point differently.

If there are any issues with the serpentine drive on the front of the engine the water pump does not turn. I've limped out a 4.0 powered XJ with a non-op serp drive for many miles and not had anything happen to the engine that an oil and coolant change didn't fix once the initial pulley failure was addressed. The oil and coolant looked ok actually, just was being proactive considering how many times the engine was swung into the red before shut down and cool off.

With an aluminum head luck may not be as good.
 

reece146

Automotive Artist
Research the differences of the 99+. It has a modified head and intake for emissions reasons. The intake manifold is better but the head is restricted on the exhaust, still produce the 190hp.

My understanding is that the MY00+ head flow is tuned to make better power/torque at highway speeds in order to not bog under load. It's a drivability thing versus chasing a peak number.

Build a 4.5 - 4.6 stroker and you'll have all the power you need or want.

I was asking where you were in order to ascertain whether high altitude driving is a factor. I'm guessing not much, makes a better case for staying with the inline six as well.

My MY01 XJ has a stock engine and has a curb weight of ~4350 lb the way it is built. It has plenty of power for hauling itself around.

My advice is focus on getting the Jeep running and sorted with a 4.0 swap and then worry about modifying for more power later after it is drivable again. You can bench build your stroker bottom end in parallel if you wanted while still having a vehicle to drive. None of this Jeep stuff is very expensive so it's kind of a no-brainer that way.
 

MrBeast

Explorer
My understanding is that the MY00+ head flow is tuned to make better power/torque at highway speeds in order to not bog under load. It's a drivability thing versus chasing a peak number.

Build a 4.5 - 4.6 stroker and you'll have all the power you need or want.

I was asking where you were in order to ascertain whether high altitude driving is a factor. I'm guessing not much, makes a better case for staying with the inline six as well.

My MY01 XJ has a stock engine and has a curb weight of ~4350 lb the way it is built. It has plenty of power for hauling itself around.

My advice is focus on getting the Jeep running and sorted with a 4.0 swap and then worry about modifying for more power later after it is drivable again. You can bench build your stroker bottom end in parallel if you wanted while still having a vehicle to drive. None of this Jeep stuff is very expensive so it's kind of a no-brainer that way.

that is what I am looking at, I am trying to find a 97-99 as I have heard the 00& up have head cracking issues, going to pull the motor complete with the computer and wiring harness, get it running with that and the NV4500.

High altitude will be an issue, I am moving to Alaska in the spring, and will be spending part of the winter in Montana.
 

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