Join Date: Mar 2003
Location: Fairbanks, Alaska
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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.
I will start using Metric only when the duodecimal system is adopted!!