This has been discussed numerous times.....numerous times.....
The 'suggested' route is to do a search first....both here and on the web. You will find a ton of information....because it has been done 'numerous times'.
BTW....welcome to the board....don't want to discourage you from being active...but, please try the search function first....especially on a subject like that, that has been discussed 'numerous times'.
I assume that you have an early 4.0L YJ or Cherokee and want to put the newer 4.0 HO head on it. I have heard lots of people swapping the the 4.0 head onto the 4.2 Jeep, but have not heard of many 4.0 to 4.0 swaps.
I have a 4.2 with the 4.2 head, so I am not help. I did search google for the 4.0 to 4.0 HO head swap, and really did not find much.
I did find some information about the different 4.0 motors and intake manifold differences and years to stay away from because of emissions changes, but nothing on a 4.0 to 4.0 head swap.
All I can say, is spend some time searching. I'm sure that someone has already done it.
Was that a head design change or just the introduction of MPFI? I was under the impression that the 4.0 head was designed after the 2.5 head which had much better breathing capability. I wasn't aware of any further evolutions in design. Impressions are funny things, though.
87 to 90 Renix MPFI engines used heads very much like the 258 heads.
91 and up used the High output heads but they are not all created equal. To use any of them you will need a HO exhaust manifold but the stock (1980 and up) intake can be made to work.
91 to 97 ish used the 7120 casting number heads. These are considered to be the best of the HO heads and had large exhaust ports.
98 and up used a smaller exhaust port to improve warm up times for the O2 sensor. This caused a drop in power, which was compensated for with the new intakes. There were two different casting numbers used and I can't remember when they switched, performance wise they are basically the same though. In the early 2000's, I think 03 was the worst year, some of these heads were found to have porosity problems. Between the smaller exhaust and posible porosity problems it is just better to use the 7120 casting heads.
There is no reason swapping a HO 4.0 head onto a non HO 4.0 should not work. The 4.0 block changed very little or not at all between the 2 so there should be not problems there. Any issues will most likely be with little but still important things like bolt hole for accessories. However, these should be able to be worked around.
You are not likely to find much information on the CJ/YJ/TJ boards as the non HO 4.0 was never used in those Jeeps. Try the Cherokee boards as they use the non HO 4.0, and someone has to have done this in the past. Also look at some of the dedicated 4.0 stroker sites, many of these folks know so muchabout the various 4.0's it will make your head spin. In fact one of the first strokers was done on a Renix 4.0
Sorry I can not be of more help.
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