258 .60 4.0 head - JeepForum.com
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post #1 of 5 Old 03-21-2006, 09:37 PM Thread Starter
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258 .60 4.0 head

pulled my engine and sent it to the machine shop boring it out .60 over and putting a 4.0 head on, with a 4 brl carb any one know the power gain about from what im doing?? i know the head swap alone is around 40 or so from what ive read on other sites from people doing it

1989 yj 4.2L, 3" rough country lift, 2" body, 1.5" shackle lift, sye, 35x12.5 cooper discovery stt's, costom rear bumper with d ring mounts, 4 brl holley 390cfm, offenhouser 4brl intake manifold, hollowed out cat, dynomax straight through muffler, t-case out of a ram, 4.11 gears, super dana 35 kit with detroit
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post #2 of 5 Old 03-21-2006, 11:06 PM
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1986 CJ7 
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I have never heard of any actual numbers from a dyno, just seat of the pants impression. There are other factors like exhaust, cam, etc, so everyone will be a bit different.

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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post #3 of 5 Old 03-22-2006, 11:35 AM
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1991 XJ Cherokee 
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If you don't do any other mods (cam, intake, exaust) probably 200ish. But it'll be WAY torqueier. When you accelerate from a stop it'll haul.

"Nitrous? So is that like viagra for your Jeep?" -mom

"I flopped it"
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post #4 of 5 Old 03-22-2006, 12:46 PM
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1997 XJ Cherokee 
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Check out Clifford Performance's website, they offer some insight on the swap... tehy sell the whole kit I think.

'97 XJ... 4.0 4x4 AW4. 2" budget boost w/t-case drop.
31x10.5 Cooper Discoverer ST's on 15x7 Cragar Soft 8's.
Intake, Ported TB, TB spacer, Super 40 Flowmaster.
Baja Aux. Lighting.
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'04 WJ - Columbia Edition - 4.7HO 2WD
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post #5 of 5 Old 03-22-2006, 03:16 PM
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I had a 4.0 head on my 258 with the 390 holley and offenhouser intake and let me tell you that puppy would break the 35's loose with ease. Out ran my wifes new Liberty until my gear ran out(4.10). Boring it out will only increase the power. You may even want to look into a HEI distributor from about a 72 chevy van with the 250 six cylinder. Only thing is you have to put a v8 drive gear on it from an amc v8. That helped me out by opening up the gap on the plugs. You may even be able to up the carb size to the newer 470 cfm truck avenger.

89 YJ upgraded with 95 Chevy LT1 small block, NV4500 5spd, tera low 231 SYE, Custom built crossmembers and skids, 2003 Corvette Electron Blue paint, 3 inch custom spring lift with 2 inch shackles, 2 inch body lift, locked 8.8 with discs, 4:10's and 35's, spray lined tub, and a few other unmentionables
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