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1979 4.2L 258 Upgrade options?

Swaping 258 to 4.0, 4.0 parts to 258 etc!
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kegwalker
Posts: 3
Joined: January 14th, 2021, 5:03 pm
Vehicle Year: 1979
Vehicle Make: jeep
Vehicle Model: cj-5

1979 4.2L 258 Upgrade options?

Post by kegwalker » January 14th, 2021, 5:54 pm

Hi all, new to the site and I'm looking to modify!
I have a 1979 CJ5 with the 258, bone stock (with exception of a weber 38 carb i put on it ~15 yrs ago).
I live at 9500 ft elevation, and when I take it out sometimes go up to 12,000 ft, and can also take it down to moab at ~3500 ft elevation.
I am currently having problems with getting fuel on steep uphills (worn cam lobe?) and also tired of it running too rich and my wife hates the smell of unburnt (and non- cat) petrol.
Therefore, looking to modify it (I want to keep the 258 block - good compression on all cylinders, does not burn oil, etc.) and go with some sort of fuel injection.

So, I am curious about the 91+ YJ/XJ 4.0 head and EFI or other options (the Holly Sniper MFI?)
I've gone through a few old articles (~2007) of this swap and just wondering if this is still a good option, or if anything new is out there.
The Mopar kit seems pricey, and the only one I can find is for 1981 and newer.
A couple of years ago with this on a wish list in my mind, I did buy a rebuilt head 0630 casting, wiring harness and ECU for like $150 - low enough that if the better option is to start fresh, i'm ok with that.

Any thoughts and suggestions?
Anyone in Colorado that has experience with this?

Cheers!

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derf
Posts: 6
Joined: November 23rd, 2020, 9:12 am
Stroker Displacement: 242
Vehicle Year: 1987
Vehicle Make: Jeep
Vehicle Model: Comanche
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Re: 1979 4.2L 258 Upgrade options?

Post by derf » January 18th, 2021, 7:03 am

Depending on where you are, the emissions requirements on that 79 may require periodic inspection. Less frequent with a classic vehicle but still not exempt.

Howell makes a reasonably priced throttle body injection kit for the 72-80 CJs that is CARB compliant (no problem with emissions): https://howellefi.com/product/tbi-kit-1 ... ons-legal/

It's less complicated and less expensive than a full multiport fuel injection system. It will solve the problems of altitude, running rich, and off camber loading up/starvation.

When it comes to the stink and making the wife happy though, a good (CARB compliant as required in Colorado) high flow catalytic converter doesn't restrict exhaust flow but it does get rid of the stink.
1987 MJ project: 4.6/AW4/ORD Magnum Box/Ford NP205/Dana Super 60/Dana 80/40's
2001 XJ: 4.0/AW4/NP242/D30/D44/32's
My gear ratio calculator: http://www.grimmjeeper.com/gears.html

kegwalker
Posts: 3
Joined: January 14th, 2021, 5:03 pm
Vehicle Year: 1979
Vehicle Make: jeep
Vehicle Model: cj-5

Re: 1979 4.2L 258 Upgrade options?

Post by kegwalker » January 18th, 2021, 10:48 am

No emissions where I live so anything I do is fine (I’ve had it licensed here for the past 20 years).

Thanks for the link to the Howell kit, I’ll look into it.
It doesn’t seem like the Jeep 4.0 top end swap is overly complicated, perhaps the port injection is the best method. I need to do more research on that though. Unfortunately, the closest junkyard is an hour plus away. No problem if I get everything at once, but a pain if I need to return to grab anything else.

And yes, I have been looking at adding a hi flow cat- I’ve been waiting to see what changes I make to the engine (and potential exhaust) before welding something on.

Thanks!

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derf
Posts: 6
Joined: November 23rd, 2020, 9:12 am
Stroker Displacement: 242
Vehicle Year: 1987
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Vehicle Model: Comanche
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Re: 1979 4.2L 258 Upgrade options?

Post by derf » January 18th, 2021, 11:54 am

I'm in Castle Rock and I go to the yards on a somewhat regular basis. If you tell me what you're looking for I can probably grab it and figure out a way to get it to you. :cheers:

As far as the cat, you should be able to just add one independent of what system you end up with. Most of the fuel injection systems just need the O2 sensor hooked up before the cat. Even on trucks that don't require it, I go with a cat anyway just because I don't like the smell. And it helps mellow the exhaust sound.
1987 MJ project: 4.6/AW4/ORD Magnum Box/Ford NP205/Dana Super 60/Dana 80/40's
2001 XJ: 4.0/AW4/NP242/D30/D44/32's
My gear ratio calculator: http://www.grimmjeeper.com/gears.html

kegwalker
Posts: 3
Joined: January 14th, 2021, 5:03 pm
Vehicle Year: 1979
Vehicle Make: jeep
Vehicle Model: cj-5

Re: 1979 4.2L 258 Upgrade options?

Post by kegwalker » January 19th, 2021, 7:55 pm

derf wrote:
January 18th, 2021, 11:54 am
I'm in Castle Rock and I go to the yards on a somewhat regular basis. If you tell me what you're looking for I can probably grab it and figure out a way to get it to you. :cheers:
That’s a heck of an offer! I’ll shoot you a PM.

I’m thinking the port injection with junkyard 4.0 parts is probably the best bet- although also tempted by a complete 4.0 then stroking it out with the 4.2 crankshaft and rods.

bnelson
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Re: 1979 4.2L 258 Upgrade options?

Post by bnelson » January 20th, 2021, 8:08 am

kegwalker wrote:
January 19th, 2021, 7:55 pm

by a complete 4.0 then stroking it out with the 4.2 crankshaft and rods.
That sounds like the correct option :cheers:

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