4.0 head swap - JeepForum.com

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post #1 of 2 Old 12-07-2013, 08:16 AM Thread Starter
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1985 CJ7 
Join Date: Nov 2013
Location: Hanover
Posts: 4
4.0 head swap

I just bought my first jeep, 85 CJ7. I am tearing down the engine to reseal, re-ring, re-cam, and replace the head. I called my local machine shops and for them to re-do the head (clean, new guides, valves, seal, etc) would cost me $300-$500. I did some searching and found this site.


I can get basically any head I want for about $186. I have also read about 4.0 head swaps increasing hp. If I go this route, I know I have to get a 4.0 Exhaust, but what other things will I have to get? What year 4.0 is best for the swap?

I don't have a lot of money so I want to keep this as cheap as possible, but if I am replacing the head anyway, would it be worth the time and money?

As far as intake, i plan on keeping it carbed but upping the cfm. should I go 500cfm or keep it lower around 390?

thanks in advance.

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post #2 of 2 Old 12-07-2013, 07:45 PM
1982 CJ8 
Join Date: Nov 2011
Location: Clearwater
Posts: 378

There is a ton of information on the swap if you google it. Try "jeep 4.2 to 4.0 head swap". The general consensus for the 4.0 head seems to be 1991 to 1994(5?). It will have 7120 cast on the top. If you've got a pick an pull junkyard, any Cherokee/Grand Cherokee will work. This article seems fairly complete http://offroad-review.com/new/index.php?page=68 . Fairly decent discussion/info here http://www.jeep-cj.com/forums/f2/258...-results-8500/ .

A lot of people seem to like the 470 Avenger carb for its off-road performance. Any higher cfm than 500 is over kill, 390 is plenty.

Full disclosure - I haven't done the swap. Just did a lot of research. I ended up putting in a stroked 4.0. Hopefully some one with real experience will chime in and not just throw a bunch of links at you . You may want to check out/post over at the CJ Forum as well http://www.jeepforum.com/forum/f8/ .

Good Luck
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