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Unread 08-10-2004, 01:44 PM   #1
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1981 CJ5 
Join Date: Jun 2001
Location: Salt Lake City, utah
Posts: 32
4.0 head, fuel economy

Has anyone out there swapped a 4.0 head on his/her 258? I'm thinking about putting a 4.0 on my 232 and I want to know if I'll see increases in fuel economy as well as increases in power. Currently I'm getting about 16 mpg.



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Unread 08-10-2004, 02:05 PM   #2
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1980 CJ5 
Join Date: May 2002
Location: Hawaii
Posts: 6,146
I wonder if it would fit. The 4.0 head fit only 81 and later 258's and the 232 is similar to the earlier 258.
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Unread 08-10-2004, 05:52 PM   #3
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1986 CJ7 
Join Date: Jun 2004
Location: Monroe, WA
Posts: 1,595
I wonder if it will fit also. I didn't know there was a difference between the 81 and later 258 blocks.

I have the 4.0 HO head (7120 cast) and see about 15 mpg with 4.10 gears and 31" tires with T5 trans. I drive with a pretty heavy foot so I'm sure I could squeeze a couple more mpg but it wouldn't be as fun. The head mod ain't for mileage but some poeple see some good gains when running a FI setup.
1986 CJ7, 4.2 w/4.0 head, TFI-HEI hybrid ignition, Clifford manifold w/Holley 390 w/cold air intake, OBA, 4.5" lift, Woody CV shaft and Tattons in front, 4.10 gears - lunchbox in front, Truetrac in the back, twin-sticked, blower upgrade for running topless, trying to keep it simple.

It's just a Jeep, and if you don't wheel it once in a while, it's not even that.
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