Join Date: Sep 1999
Location: San Diego, CA
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Re: Will a 4.0 head from a Cherokee fit a 258 4.2L
The head will fit. The 4.0 heads have better combustion chamber config, plus bigger intake valves (= more HP). The '90 cherokee head will either be an HO with the Mopar MPI (casting number 7120) or it will be the head that came with the Renix fuel injection system. The only real difference is a slightly different exhaust port height and the fuel injection system.
I didn't understand what the question was related to the carb and intake?? Whe you talk about putting the '90 head on are you also talking about putting the fuel injection and intake? If so, I think the fuel injection is the way to go, but it involve quite a bit more than just the head. You have to figure out wiring, computer, fuel pump, sensors, etc.
The 4.0 head is quite a bit better than a 4.2 head and could be swapped using the same carb/intake. There are some on this board who have done this without switching to fuel injection and like it. It is believed to add anywhere from 15-40 HP with the head swap alone.
If you are planning to do more than just the head swap, you should really research 4.0 head with the search function. There is a ton of info out there.