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Unread 06-26-2005, 07:17 PM   #1
'83Laredo
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Your opinions: complete 4.0 swap or just 4.0 head swap?

I have the chance to buy a complete running early-mid '90s Jeep p/u truck (I think it was the Comanche?) for $500. It has the 4.0.

My 258 was rebuilt by the previous owner. It doesn't have many miles on the rebuild.

Should I rebuild and swap in the whole 4.0 w/MPFI, or just use the 4.0 head and MPFI on my 258 block?

I want something that will run on regular gas (87) and have a significant power increase. What would you recommend?

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Unread 06-27-2005, 05:57 AM   #2
jadams68
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I wouldn't swap in a high mileage 4.0L from that commanche to replace your rebuilt 258.

If you were engine swapping, find a low milegage 4.0 from a cherokee or grande cherokee.

I just rebuild my 258 and put a 4.0L HO head on it. I run a Howell TBI injection system and I'll be finishing it and firing it up within a week.

I'll post my results.
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Unread 06-27-2005, 06:48 AM   #3
'83Laredo
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I would have either the entire 4.0 rebuilt if I went that route, or just the head rebuilt if I went that route. I'm definitely not putting a non-rebuilt engine in the CJ.

Doesn't the 258 have more torque at lower RPMs?

Has anyone ever had the 4.0 head/258 block combo on a dyno to actually see the results, instead of estimates? I've read that this combo gives you the best of both worlds, but I haven't seen any data to back it up.
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Unread 06-27-2005, 06:57 AM   #4
jadams68
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The 258 does have more low end torque and the 4.0L HO head has a better design to draw fuel/air and push out exhaust more efficiently.

The net is close to 40hp, but you're right...no one has dyno'd this... I will definitely do that and report.
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Unread 06-27-2005, 07:15 PM   #5
rcsutton
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jadams will your new engine be running on 87 octane? I'm watching your rebuild.
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Unread 06-27-2005, 08:11 PM   #6
TheJunkMan2005
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Where can I find a write up on this online? I've junked out 5 or 6 cherokee/commanche trucks in the last few months, and didn't realize this was worthwile.. I don't want to tie up this post with with this is good and such, but a websight about it would be cool.

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Unread 06-27-2005, 08:26 PM   #7
n3480h
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I believe you can find info on this at http://www.geocities.com/cantwait_forviolence/

This is Geer Hed's site, one of the best collections of CJ info I've seen.
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Unread 06-28-2005, 05:25 AM   #8
jadams68
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I honestly don't know if it will run on 87 without pinging, but there's 3/4 of a tank of 87 in it now and that's what it's going to be broken in on.

At this point I simply need to wire it up and put on the fenders and grill...then turn the key... my goal is to fire it on or before July 5th...
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Unread 06-28-2005, 07:33 PM   #9
rcsutton
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Quote:
Originally Posted by jadams68
I honestly don't know if it will run on 87 without pinging, but there's 3/4 of a tank of 87 in it now and that's what it's going to be broken in on.

At this point I simply need to wire it up and put on the fenders and grill...then turn the key... my goal is to fire it on or before July 5th...

Hope there are no fireworks. Keep us posted.
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Unread 05-22-2011, 05:04 AM   #10
o2tj
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Its really worth getting the 4.0 (or head swap) in a old cj. I love mine. Nothing like reaching in the window and turning the key an having it fire right up. You can follow my build here:
http://novajeepers.net/index.php?topic=819.0
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