Rebuild 258 or 4.0 HO? -
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back > Models > Jeep CJ Forum > Rebuild 258 or 4.0 HO?

Corbeau Seats & Harness from CCOR!Smittybilt Seat Covers and Tailgate CoverClearance & Overstock Jeep Parts New and/or Used at th

Unread 06-11-2010, 07:35 PM   #1
Registered User
1979 CJ7 
Join Date: Jul 2009
Location: Modesto
Posts: 58
Rebuild 258 or 4.0 HO?

I have been battling between rebuilding my 258 or buying a 4.0 HO from a newer wrangler for my 79 CJ7. What are the positives/negatives of each option? If i decide to rebuild the 258, should I go with the howell or mopar FI kit? Does anyone know about how much it will cost for each option? Also, if you have rebuilt your 258, what parts did you use and would you use them again?

1979CJ7newguy is offline   Reply With Quote Quick reply to this message
Unread 06-11-2010, 09:06 PM   #2
Registered User
1999 WJ 
Join Date: Aug 2008
Location: Long Island,NY
Posts: 207
I pretty much did a rebuild on my 258. It's a great engine. I've been dealing with almost every iteration of Inline 6 Jeep motors since they started building them. Absolutely nothing wrong with it. Now if you want to upgrade your setup that is another story. You could keep the 258, throw on a 4.0 head and then it allows you to run the fuel injection setup. Or you just keep the carbureted intake configuration on the 4.0 head, it all bolts right on. You may have some MINIMAL clearance issues with the stock 4.2 carb intake and 4.0 exhaust manifold. It is easily dealt with. But you do have to use the 4.0 exhaust manifold. Keeping the engine you have and modifying it is the cheapest and easiest solution. Hope that helps
BULLITTBUilder is offline   Reply With Quote Quick reply to this message
Unread 09-29-2011, 10:35 AM   #3
Registered User
1986 CJ7 
Join Date: Apr 2010
Location: Whitehouse Stn,NJ
Posts: 1,456
The carbed 4.2 and the FI 4.0 are like night & day. 4.0 has way more power. Or like stated put a 4.0 head and FI setup on your 4.2. I saw just last weekend a complete running 4.0 go for $150 at a swap meet. The dude gave it away..
CJ7ROB is offline   Reply With Quote Quick reply to this message
Unread 09-29-2011, 10:39 AM   #4
Registered User
1979 CJ7 
Join Date: Jul 2010
Location: Burlington, Vermont
Posts: 935
The 4.0's are a dime a dozen here too. If you do the 4.0 head on the 4.2 does the FI still run okay? The tuning is alright?
Wheel - Wreck - Wrench - Repeat!

The VIN says its a 79 CJ
79jeepincj7 is offline   Reply With Quote Quick reply to this message
Unread 09-29-2011, 09:45 PM   #5
Registered User
1983 CJ7 
Join Date: Feb 2006
Location: Indianapolis, Indiana
Posts: 3,441
The 4.0L engine is great. I run mine carbed but running it as with its native FI is great as well.

Given the choice between rebuilding the 4.2L and a 4.0L, I'd rebuild and install the 4.0L.
Vibration? Bump steer? Wandering? Read the article (sticky) on Steering, suspension, and driveline.
gojeepin is offline   Reply With Quote Quick reply to this message
Unread 09-29-2011, 10:14 PM   #6
Registered User
1981 CJ7 
Join Date: Jul 2009
Location: Bali, Indonesia
Posts: 5,120
You are probably looking at around 100hp from your current engine in old and worn state as opposed to 160-170hp on a used 4.0 HO. I know they could new generate 190+ but you wil not get this unless you spend bucks on a rebuild.

That is one helluva step up in power.

Downside is that you will need the whole engine, fuel injection, wiring and computers to make that swap. the most difficult part for a home mechanic is the wiring, it is a mass of spaghetti and unless you have an affinity for that sort of stuff it could ruin your build. Some do and make it look easy.

Another route is a 4.0 head on carbs on a 4.2 block. Opinions vary but it could add 30-40hp on a 4.2. If you rebuild the block as well with new rings etc. you could be seeing 150hp+, maybe 160hp. It would not have the complexity of fuel injection and hence is fairly straightforward for a home mechanic.

If a 4.0 head with FI on a 4.2 block you could exceed the power levels of a 4.0HO. I say "could" as that will take some degree of skill but it is quite possible to use the 4.0 injection on a 4.2.
BagusJeep lives in Bali.

1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
BagusJeep is offline   Reply With Quote Quick reply to this message
Unread 09-30-2011, 12:04 AM   #7
Registered User
1986 CJ7 
Join Date: Dec 2008
Location: tijuana
Posts: 122

i have this set-up in my 4.0

2001 block
1995 head h.o.
intake 4.2
carb carter dodge + jeep
exhaust 1995
dana 300 without adapter
distribuitor motorcraft update tfi
accel super coil
autolite xp gap .055

its a monster in rpm. i use the 4 shift every time

INKUBUS is offline   Reply With Quote Quick reply to this message

Quick Reply

Register Now

In order to be able to post messages on the forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools

Suggested Threads

Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. is not in any way associated with Jeep or the Chrysler Corp.