post #1 of Old 06-14-2007, 10:56 PM Thread Starter
arock1278
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4.0 non-HO manifold on HO head

Sorry if this has been answered before, I could swear I read about it somewhere, but I can't find it for the life of me.

Will a non-HO manifold fit on a HO head? I've got a MPI setup from a 87 or 88 4.0L. I'm wondering if I get a HO head if I'll be able to use it. I'm not worried about the computer or sensors or any of that. Just if it will physically bolt up to the head. I know they raised the intake ports some, (and used different injectors and a bigger throttle body and what have you), but did the actual bolt pattern change? Can I just raise the intake however much and bolt it right on? If so, which gasket would I use? The HO gasket or non-HO? Thanks.

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post #2 of Old 06-15-2007, 10:16 AM
Happy Joe
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I have put early 4.0 MPI manifolds on both a 258 and a 4.0 high port head ('97) A little grinding was all that was necessary (gaskets will tell you where). Use the HO gasket to install. I, personally, would go with the HO manifold & TB though, if available.

Enjoy!
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post #3 of Old 07-13-2007, 02:28 PM Thread Starter
arock1278
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Hmm, I didn't think it would fit on a 258 head. I got the intake originally for that reason, but after looking at it I didn't think it would work, so I was thinking about doing a head swap instead. I never got to it though, and just recently had to change the manifold gasket, and it does look very similar.. The one thing that would worry me is the little jut out where the injector is. It seems like not much gas would be able to get through. I'd use an 87 gasket, but then the exhaust ports are way wrong (round instead of square). What gasket did you use on the 258? Did everything seem to run OK?
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post #4 of Old 07-14-2007, 10:11 AM
Happy Joe
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Tightly stuff a small rag in each intake port (use caution if the grinder grabs the rag you could be injured), mark the head using the gasket as a template, then use a die grinder and a cylindrical stone to cut an injector relief into each intake port (stop grinding at the edge of the mark (when in doubt leave a little extra on the sealing surface) and use the injector angle in the intake as a visual indicator as to how much to grind at what angle. (Don't forget to vacuum out the chips and remove the rag from each port).
As long as the air can flow down over a step (instead of running into the step or wall) it will work fine. Some bolt clearances may need to be ground to make them fit and at least one ear (for the washer that holds the manifold) needed to be ground for clearance. It will need custom brackets (or just don't attach the upper bolt of the power steering bracket).
This was the best engine modification I ever did for off roading. It ran great. I was severely disappointed when I replaced the 258 head with the 4.0 HO head and got nothing in return performance wise (others have seen good benefits though).
Enjoy!
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