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Unread 01-01-2010, 06:18 PM   #1
deezil
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1996 4.0 Head worth swapping onto 258?

I recently got a nice 4.0 1996 head off of a low mile Cherokee.

I want to do the head swap on my 1985 AMC 258 But since this is the later head is it worth doing or should I just look for a earlier head?

Thanks ahead of time.

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Unread 01-01-2010, 06:29 PM   #2
fredrok
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casting numbers you want to look for:

1991-95......7120
1996-99......0630

The '91-'95 HO heads with casting no.7120 have the highest intake and exhaust port airflows, especially at lower valve lifts where it is most important, and are the best for performance. The '96-'99 0630 heads are almost identical except that they don't have a port for the coolant temp. gauge sending unit.
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Unread 01-01-2010, 06:37 PM   #3
deezil
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I Think mine is the 0630 head. It's getting hot tanked now, so I will check for sure when I get it back.
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Unread 01-01-2010, 11:23 PM   #4
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Quote:
Originally Posted by fredrok View Post
casting numbers you want to look for:

1991-95......7120
1996-99......0630

The '91-'95 HO heads with casting no.7120 have the highest intake and exhaust port airflows, especially at lower valve lifts where it is most important, and are the best for performance. The '96-'99 0630 heads are almost identical except that they don't have a port for the coolant temp. gauge sending unit.

It should be noted that the comment about the 7120's flow rates matter more if you aren't planning on any flowbench work. Once you start working 4.0 heads, getting any particular casting number for the purpose of cfm is less important, as the other castings get "brought up to speed" by the mods.
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Unread 01-02-2010, 12:00 AM   #5
deezil
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I Just plan on just polishing it up a bit and calling it done. It came off of a late 1996 Cherokee I think its safe to say its a 0630 and so far from what I read while searching the net it isn't all that bad of a head.

Lets hope it's a good core when the shop takes it apart.
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Unread 01-02-2010, 08:45 AM   #6
fredrok
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Blend the radii where it transitions from the port to the bowl area, then clean up the area of the bowl where it meets the seat AFTER the 3 angle valve job is performed (see pic below). Clean up and smooth any areas in the combustion chamber that are sharp-your goal is to smooth them and remove as little material as possible in the chamber-(see pic), both of which will require you to be very careful not to nick the seat area. You can also use the gasket to set your profile and raise the roof area of the exhaust port if it requires it (assuming your exhaust manifold or header matches the exhaust gasket) and then LEAVE THE REST ALONE.

Unless you're going with MPFI, do not bother to polish anything. You'll waste your time and likely make atomization worse. (when the design is already bad anyway)

Without a flow bench and experience, you'll get much better results from these small improvements than you would going hog wild porting and polishing. Good luck and have fun.

This was taken after a quick job I did many moons ago on a 258 head before I converted to a 4.0. Same rules apply.

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Unread 01-02-2010, 12:46 PM   #7
wendell
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To get the most benifit from the 4.0 head swap, also intall comp cam exteme energy 4X4 cam # X4250H. This will also allow you to run a holley 470 TA 4 barrel and offy intake. It will take the fuel of a 470 instaed of having to run the 390. The holley TA series 4 barrels are made for off road and can handle some extreme angles. The 4.0 head a long with the cam is good for about 40 extra hp. The head a lone won't get you there like alot of people say.
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Unread 01-03-2010, 11:27 AM   #8
Boodie
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I LOVE my 4.0 HO Head conversion! Better mpg, better compression, more HP. If you're not building a hot rod/drag racer then it's the way to go!



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Unread 01-03-2010, 12:34 PM   #9
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I was looking at one point to do a 350 swap but after reading other posts it seems like lot more work than I am ready for. I have a 79 with a donor 258 in it. I also have the original motor. I read somewhere only certain year blocks can be used for this swap. For that matter it seems like lot of upgrades and parts only apply to '81 and newer why is that aren't all 4.2 258's made the same?
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Unread 01-03-2010, 01:12 PM   #10
deezil
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I know of someone that has used a 4.0 head on a 1972 258........ I assume it will pretty much work on any 258
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