Calgary Jeep Association

4x4 Related Groups => Tech Talk => Topic started by: 80CJ on January 30, 2007, 05:27:27 PM

Title: 4.0 Head to 4.2 Block
Post by: 80CJ on January 30, 2007, 05:27:27 PM

Sorry if this has been asked and yes I know about the search function, but here's the ???

I have this new CJ7 (1980) with the 258 and a bad head. If I wanted to swap on a 4.0 head (As we've heard this can produce some power gains) rather than do a stroker build by using the whole 4.0 block what numbers would I have to cross reference to get things to bolt up? I know some other things like intake and what not would have to be changed but I'm just in search of a head. I think the one I have will run for now, but this sounds interesting and low $$$ if I do it right. Any suggestions or directions? We've found a blown 4.0 with a good head for 5$, just don't know if it would bolt up.

Title: 4.0 Head to 4.2 Block
Post by: gsxtacy on January 30, 2007, 06:41:37 PM

i have looked at this in my cj-5 and found it's too much of a pain in the butt.  (my jeep is daily driven, so i can't afford the down time). you have to change out your entire exhaust manifold/intake setup i think and maybe some other stuff too.  when i evaluated it for my 4.2 i figured it just wasn't worth the time and energy.  the only major difference i believe is the intake ports are milled differently, so instead of a 90 degree drop to the valve, there's a bit of a slope.  because you also have a newer 4.2, i think you'll hafta change out the head bolts too.

don't quote me, i just read it somewhere...you're better to take your head in and have it milled out like i did, and i didn't really notice any power gains, just an increase in fuel consumption xD

Title: 4.0 Head to 4.2 Block
Post by: 80CJ on January 30, 2007, 06:53:34 PM

Well my head now is pretty much not fixable. Not sure what happened to it but 3 of the head bolt holes are broke out pretty good. It'll run for now, but if I do what I did w/ the last CJ and put on a 4 barrel, headers, and Offy intake then I still have to swap the parts, so might as well get parts for a 4.0 instead of a 4.2.

Title: 4.0 Head to 4.2 Block
Post by: Bnine on February 01, 2007, 09:06:06 PM

You need to block some water jackets. Might have to drill a hole or two in the front to line up bracketry.

You need to die grind the end bolts on your 4.2 intake to fit the 4.0 head.

You need a 4.0 header.

Head you are looking for has to be from 91-99 to be worth the swap.

Casting numbers you are looking for are 0630, or 7120.

Search around, there are a lot of articles on that swap.

Title: 4.0 Head to 4.2 Block
Post by: NS-jeeper on February 01, 2007, 10:34:54 PM

what about droping in a whole 4.0L, then you'd have fuel injection :)

Title: 4.0 Head to 4.2 Block
Post by: 80CJ on February 02, 2007, 07:30:00 AM

I'll stick w/ my carbed 258. Thanks for the input Bill. Now just gotta find me a head.