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post #1 of (permalink) Old 06-24-2003, 01:02 PM Thread Starter
 
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4.0 vs 258 w/4.0 head

I'm trying to figure out what I'm going to do with my 85 CJ7. It has a fairly peppy 258 in it that we just dropped a motorcraft 2100 on. Down the road however, I'm going to want more power. I've checked the local junkyards, but none of them have a 4.0 head and fuel injection that I can get to drop on the 258. However they DO have a complete 4.0 with the fuel injection and computer for $800 (I didn't ask the exact year, but I had asked for any 4.0 1994 or newer). If I decide to bite the big one and buy the engine, what will give me more power? Dropping the 4.0 straight in, or taking the 4.0 head and MPI and putting it on the 258?

Also, how difficult is the 4.6L stroker mod?

Thanks guys!
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post #2 of (permalink) Old 06-24-2003, 03:40 PM
 
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Re: 4.0 vs 258 w/4.0 head

Honestly, if your 258 short block is in decent shape, I'd just swap the head & MPI onto it... Both projects will probably take the same amount of time, more or less... By keeping the 258 block you're getting the longer stroke that makes it such a torquey engine.... All while still benifiting from the higher flow of the 4.0head and added horsepower of the FI setup. I'd love to be running that setup someday... for now i'll just have to stick w/my 4.0 head/carb. Sigh.
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post #3 of (permalink) Old 06-24-2003, 04:50 PM Thread Starter
 
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Re: 4.0 vs 258 w/4.0 head

Thanks. I had a feeling that the extra stroke/displacement of a 4.2 with 4.0 would be a bit stronger than the straight 4.0, but I wanted to hear from somebody that had one before I took that fact to the bank. Out of curiosity, how noticeable was the improvement?
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post #4 of (permalink) Old 06-24-2003, 08:01 PM
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Re: 4.0 vs 258 w/4.0 head

I have been wondering the same thing, Lets hear some more info on this! I'm kinda thinking I'm going to do the 4.0 complete swap because it is a easy swap. When you start mixing parts or building a stoker, I think you have to guess a little on what works. I would think that the extra 0.2 liters would require more fuel, so that would require the computer to be reprogrammed and/or bigger injectors. My understanding is that a complete 91-95 HO engine with a PCM from a manual trans vehicle will be the easiest swap. The only thing extra to buy will be the Cam sensor / crank pulley kit. Is this right ?
post #5 of (permalink) Old 06-25-2003, 01:44 PM
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Re: 4.0 vs 258 w/4.0 head

I run a 258 w/ the 4.0 head/MPI combo and a bigger cam in my CJ-7 and I have plenty of power. I did have to put a larger fuel pressure regulator to help with the pinging. I wheeled all last summer w/ 35's and 3.23 gears and was content. I can't wait for next weekend because I get to try out my new 4.56 gears. I think I will be amazed at the difference. I like this engine combo, but have never driven a compairable Jeep with just the 4.0.
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post #6 of (permalink) Old 06-26-2003, 05:10 PM
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Re: 4.0 vs 258 w/4.0 head

Do the head swap and MPI if you can shake the money. Gives you the botom end power of the 258 with the top end power of the 4.0...better all around.

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post #7 of (permalink) Old 06-26-2003, 07:10 PM Thread Starter
 
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Re: 4.0 vs 258 w/4.0 head

I can't find just the head and MPI, so if I do this swap, I'll be getting a complete 4.0. Unfortunately I just read the article on making a 4.6L stroker.....and I would have all the parts....LOL!

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post #8 of (permalink) Old 06-27-2003, 09:03 AM
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Re: 4.0 vs 258 w/4.0 head

Do the 4.6L Stroker. You won't be sorry. It's one bad setup. Just plan on getting some bigger injectors. i.e. off the 318 motor. And an adjustable fuel pressure regulator.


Then you'll be the man (in the I6 world).....
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