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Unread 02-25-2009, 02:58 PM   #1
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1993 YJ Wrangler 
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4.0L cylinder head mod

im going to have my cylinder head off of my 4.0L, no reason to list why cause that not the point of this thread. does anyone have suggestions for performance mods to do to the cylinder head while its off?
its kind of hard to search for because all you end up getting is thread of people putting 4.0 heads on 4.2's

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Unread 02-25-2009, 04:24 PM   #2
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You could port and polish it. Just Google up port and polish a cylinder head. It is a marginal improvement in some heads. for other heads it is a great improvement. The 4.0 head already flows decent but there is always room for improvement.
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Unread 02-25-2009, 05:49 PM   #3
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Ya a gasket match, polish and clean up the bowls. Maby get some oversize valves and roller rockers if money is not a big thing.

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Unread 02-25-2009, 05:57 PM   #4
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on the 4.0 your not going to gain anything by port and polish cause your power is being used at low revs. acutally you can make power worse on engines like this with a port and polish. Roller rockers and other such things can help.
[COLOR="Red"]1987 Wrangler YJ RED[/COLOR] 4.2 5-speed, NP231, BFG 31x10.5R15 AT/KO on 15x8 gambler wheels.
[COLOR="Yellow"]Caution!!! Under construction!!!!!! Caution!!![/COLOR]
Finishing a 4.0 Cyl.head swap, Just got an AX-15 NP231J combo to replace the busted t-case and craptacular BA10/5. Adding Nutter bypass. Probably more to come before it is back as a DD!
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Unread 02-25-2009, 06:06 PM   #5
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Get rid of it and buy this:


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Unread 02-25-2009, 06:45 PM   #6
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lol at that point i would just get a later model v8 to throw in. it looks like VERY mild porting and a polish is what ill do.
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