High Output Head on 258 I6 Worth it??

qwert98 · 05-02-2007, 05:47 PM

My 86 cj7 has 200K on it and has little power and lots of smoke. I am looking to have it rebuilt (or buy a rebuilt I6), but I am wondering is it worth the few hunderd extra to get a high output head. If I replace the head, do I need to change valves? Will the new HO head provide a noticable difference? Will it kill my fuel econory (as if it wasn't already bad enough...)?

Does anyone have any recommendations on were to get one? I read a forum that said I need a head from a '92 or newer, is the newer the better - are they all the same?

How do I know what HO head will fit my engine?

Sorry for so many ??'s, but I want to make sure that I do this right - and fast,,, the weather is getting real nice here and I don't want to be out of comission too long.

SuB8HaVeN · 05-02-2007, 06:05 PM

I would say go for it. If you get a HO head, it will probably come with valves and springs already so you shouldn't have to replace them. You can utilize the push rods already in the 258 I6. Any 4.0L HO head should work on the 4.2L 258 as far as I know. I believe there is one thing you have to drill in the head to make it work, other than that it just bolts right on.

whit450 · 05-02-2007, 06:14 PM

Ask Jadams68, he's the 4.0 258 guru on this forum as far as I know.

Fatman · 05-02-2007, 06:35 PM

The bible on 4.0 head swaps:

bustedjeep.com

.

solitudetree · 05-06-2007, 01:05 PM

Go with the 4.0 head swap. It will make a huge difference and eventually pay for itself in the long run if you hold onto your CJ.

I have a used 258 engine that I got cheap to put in my current CJ. When I do that, the 258 I pull out is getting rebuilt and I'm putting on a 4.0 head.

bustedjeep.com is a good site for the 4.0 head swap since some of the other sites don't exist anymore.

80sCJ7 · 05-06-2007, 06:08 PM

It's supposed to give about the same fuel economy with about 40 more horsepower. Prior to '92 I don't think they're "HO", so yes you do want '92 or later head. There used to be an outfit on ebay that sold the heads with the unneeded water jackets welded closed, but don't know if they still do. Your intake manifold will bolt up but you'll need a 4.0L exhaust manifold and rework your exhaust connection. If your engine uses 7/16" head bolts (I think '86 did but you'll need to check it out for yourself) you'll need to either get sleeves for the head or have the block drilled and tapped for 1/2" bolts. Disclaimer: I've never done the swap, just almost at one time, so I may be full of it.

gosupes · 05-07-2007, 07:11 AM

It's a 91-94 head, casting 7120 that you want. The other head is casting 0630 from 96-99 or so but it wont have the port for the temp sender. The machine shop can drill and tap. Pre 91 is the nonn HO head which you don't want. Think about changing the cam while your at it. You will want something that has a little more lift and stays open a little bit longer for the low end torque.

jadams68 · 05-07-2007, 06:35 PM

I definitely have more hp from my 4.0 head conversion, but note...it does come with a couple of challenges.

Take my advice and do NOT use a header...go with a 4.0L Cherokee exhaust manifold because a header is a ***** to line up with the 4.2L intake manifold.

Trust me on this...I'm fighting a vacuum leak and I know it's at the manifold, but just have to find it.

All in all....a great mod.

05-06-2007, 01:05 PM	#5
solitudetree Registered User Join Date: Nov 2005 Location: Ohio Posts: 645 Profile Gallery Classifieds My Jeeps	Go with the 4.0 head swap. It will make a huge difference and eventually pay for itself in the long run if you hold onto your CJ. I have a used 258 engine that I got cheap to put in my current CJ. When I do that, the 258 I pull out is getting rebuilt and I'm putting on a 4.0 head. bustedjeep.com is a good site for the 4.0 head swap since some of the other sites don't exist anymore. __________________ [COLOR=DarkGreen][FONT=Century Gothic]All the Jeeps I've owned 79 CJ5 258 six with a weber (current vehicle) T18/Dana20 81 CJ5 258 six (driven out of Alaska thru Canada in winter with a softtop) 75 Jeep Wagoneer 360V8 79 Jeep Cherokee 258 six [/FONT][/COLOR]

05-06-2007, 06:08 PM	#6
80sCJ7 Registered User Join Date: Apr 2007 Location: New Jersey Posts: 22 Profile Gallery Classifieds My Jeeps	It's supposed to give about the same fuel economy with about 40 more horsepower. Prior to '92 I don't think they're "HO", so yes you do want '92 or later head. There used to be an outfit on ebay that sold the heads with the unneeded water jackets welded closed, but don't know if they still do. Your intake manifold will bolt up but you'll need a 4.0L exhaust manifold and rework your exhaust connection. If your engine uses 7/16" head bolts (I think '86 did but you'll need to check it out for yourself) you'll need to either get sleeves for the head or have the block drilled and tapped for 1/2" bolts. Disclaimer: I've never done the swap, just almost at one time, so I may be full of it.