Carbureted 4.0 Head: finally there and happy THNKS - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 07-02-2002, 07:22 PM Thread Starter
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Carbureted 4.0 Head: finally there and happy THNKS

Six months after getting the new motor in my '87 YJ, I can finally say that I am happy with the results. For a review (and if you're too lazy to check my prof)...

Components<ul>[*]'79 258 short block - bored .040 over, crank .010 under, stock rebuild kit[*]'95 4.0 head (new) - water jackets drilled, tapped, fitted with pipe plugs, resurfaced[*]Crane 260 cam[*]Borla header for '95 4.0 - top half of primary tubes wrapped with header tape[*]2-1/8" pipe straight to muffler (no idea what kind), no cat[*]Clifford water-heated 4bbl intake for '79 258[*]Holley 390 - jets changed to 54[*]Stock Motorcraft distributor base - spacer, Conrad brass cap &amp; button, 1 stock super-stiff spring and 1 med/stiff spring[*]MSD 6A[*]Taylor 8mm plug wires[*]Accel SuperStack coil (premium stock coil in a yellow dress, but hey it was free)[*]Champion truck plugs - gapped to .045[/list]
Problems Encountered<ul>[*]Pilot bushing hole is a different size from '79 to '87 (POS Puegot tranny). The '79 is bigger OD and ID, and actually the '87 bearing almost fit inside the '79 bushing --> ding, ding, ding. Fortunately I have a friend with a small lathe [img]images/icons/smile.gif[/img] so he took a little more out of the inside of the bushing and I was golden. [img]images/icons/laugh.gif[/img][*]Tried to go with Pacesetter headers and they interfered with the pan. They are made to wrap in front of a full rear sump. My short block has a 3/4 rear sump. In retrospect, I am happy I had to make this switch. More $$, but that Borla header is NICE!!! [img]images/icons/cool.gif[/img][*]Clifford intake caused me some headaches. Although the ports are a perfect match, the bolt tabs do not line up and are 3/8" thick. Borla header tabs are 1/2" thick. If I had the mount job to do over I would have cut some 1/2" thick aluminum blocks, shaped them with a Drimel, and welded them on. Grinding down the exhaust header tabs would also have worked, but I didn't care for the risk of getting them uneven, too thin, or the grinder grabbing at the wrong time and really causing problems. Grinding stainless is not my favorite passtime either. I also had to put a small dent in the top of the #5 header tube and grind a little off the bottom of the intake to get the ports to line up and intake to fit flush.[*]Tuning<ul>[*]I believe that most of my tuning issues were more a result of the cam, intake, and headers than the 4.0 head itself. But put all those variables together and I had some chasing to do. My biggest problem was detonation at 1600-1800 with part throttle. The problem turned out to be a combination of lean mix and too much advance at that RPM.[*]The mix was resolved by changing the Holley 390's jets from the stock 51's to 54's and a lot of tinkering with the idle mixture screws. Most sources told me to tune it by vacuum and I did, but this didn't get it close enough for me. I put a digital volt meter on the O2 sensor and tuned to a balanced mix (.5 volts) for desired idle RPM. It may not sound like much difference, but it had a surprisingly large impact on the off-idle mix.[*]1600 is where I was reaching full mechanical advance (as evidenced by a timing light and an isolated vacuum advance), so I replaced the lighter mechanical advance spring with a med/stiff one (thanks, TR [img]images/icons/wink.gif[/img]) and gave it a little preload by bending the spring hook tab ever so slightly. [img]images/icons/blush.gif[/img] I now reach full mechanical advance at about 2200.[/list][/list]
Results<ul>[*]Power: Pulls smooth from 500 RPM all the way up. 500-1500 is comparable to a stock 258. At about 1500 it starts to wake up a little more and by 2500 it is pulling like a V8. [img]images/icons/cool.gif[/img][*]Mileage: Just got back from a trip over the mountains and got 19 mpg. YEAH!!!![*]Gas: Still running 93 octane right now. Experimenting with lower octane is my next step.[/list]

What I Would Do Differently
I would have stuck with my stock intake, my Weber 32/36 (which I sold - DAMN!), and used an RV cam. I was really wanting more of a stump puller than a hot-rod. Of course I could still go that way, but replacing the cam means pulling the head and then I'm starting this tuning journey all over again. Guess I'll just have to just have to live with my hot-rod six for a few years... shucks. [img]images/icons/smile.gif[/img]

Thanks for all the help to everyone on this board. This community is awesome! Thanks especially to Jaffer for advice and access to priceless information in your web pages, and to TR for schooling me through this, a hard-to-find spring, and a wealth of knowledge that I can only hope I gleaned something from.

The search function can be frustrating at times, but holy crap there is three billion tons of knowledge in that archive!

I be one happy Jeeper these days!
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post #2 of (permalink) Old 07-02-2002, 07:47 PM
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Re: Carbureted 4.0 Head: finally there and happy THNKS

Great post!

Keep 'em comming!
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post #3 of (permalink) Old 07-02-2002, 10:29 PM
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Re: Carbureted 4.0 Head: finally there and happy THNKS

Yes, a great post,Highfill.
That's what it's all about ... giving some back.
I get a ton of e-mails about doing what you just did.
But you went the extra mile an REPORTED HOW you did it, plus pitfalls.
Now I can refer them to your post!
Good job! [img]images/icons/smile.gif[/img]
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post #4 of (permalink) Old 07-03-2002, 09:25 AM Thread Starter
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Re: Carbureted 4.0 Head: finally there and happy THNKS

Just a little follow-up...

I have heard of people getting their 4.0 heads from a lot of different places and paying a wide variety of prices, so I figure I would throw my source out there.

My head is casting #7120 from <a target="_blank" href=>Alabama Cylinder Head</a> and was $425 for a new one without a core.
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post #5 of (permalink) Old 07-03-2002, 02:28 PM
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Re: Carbureted 4.0 Head: finally there and happy THNKS

Great post Highfill.
I am planning a rebuild and was debating the advantages of the carburated 4.0 head. You have convinced me to do the 4.0 conversion. I was happy to hear that I can keep my Weber and stock intake. Could you give some more information concerning the RV cam? I'm a little lacking in cam knowledge. Also, the year of my 258 I6 is 1973 or 1974. Should I rebuild this block, or get a 1980's block for a rebuild?
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post #6 of (permalink) Old 07-03-2002, 03:46 PM
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Re: Carbureted 4.0 Head: finally there and happy T

Glad I could help!
It's EASY to teach someone that listens, and doesn't already 'KNOW' everything...

PS, you got the HEAVY spring, and there is a rare EXTRA HEAVY SPRING out there somewhere.... If you need one, let me know, and the next time I run across some I'll cut you in...

The springs should be rated with numbers, letters, or at least a uniform paint coding...
Most are rated in ounces or pounds of spring pressure, but that means nothing to the end users.

There should be a number or letter rating, there isn't...
Color coding that changes from company to company and wire gauge size and number of turns in the spring is how they are rated....
And that makes no sense at all to an end user.
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post #7 of (permalink) Old 07-03-2002, 06:37 PM Thread Starter
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Re: Carbureted 4.0 Head: finally there and happy T

TR, if the one you sent me is a HEAVY spring, then the other one in my distributor is the EXTRA HEAVY MONDO SUPER SERIOUS spring. The wire is at least twice as thick and looks exactly like the stouter spring in the pic you posted during <a target="_blank" href=;Board=offroadjeepshort&amp;N umber=742256&amp;fpart=1&amp;PHPSESSID=>this</a> post.

Fortunately, I don't think I'll need anything different than what I have now. I have a smooth torque curve, no detonation, and good gas mileage. I'm not touching anything for a while! [img]images/icons/smile.gif[/img]

Twosocks, I'm not sure what you will have to do to the stock intake to get it bolted up securely. I went straight from the stock head/intake to the 4.0 head/Clifford intake. I never bolted the stock intake onto the 4.0 head, but I would imagine that if I can get that Clifford one on there, you should have an easier time with the stock one.

As far as the block goes, I am not really up on specific design changes from one year to the next, but I would suspect that a 73-74 258 short block would be essentially the same. The one thing you want to look out for is the pilot bushing/bearing. You may want to go to your local parts store and have them pull pilot bushing/bearings for your donor block and the block you have in there now. I would also check with the T-5 manufacturer to see what size bushing/bearing it needs. Someone on this board with more familiarity with that tranny may be able to answer that question for you as well. The problem I ran into was that the hole in the end of the crank was a different size from '79 to '87, so I had to use a '79 bushing on the outside to fit the hole and fit the '87 bearing on the inside of the bushing to keep my tranny input shaft in place.

One other thing to keep in mind is if your '83 has V-belts or a serpentine belt. My '87 has a serpentine, so I had to use a reverse rotation water pump. In other words, I had to buy a water pump for an '87, not a '79 even though I was putting it in a '79 block. They looked identical (except for the impeller direction), but one was $15 and the other was $52. You can't tell the difference unless you have them sitting side by side or you know to look for the little "R" stamped on the impeller.

Edited: Almost forgot... several manufacturers make an RV cam. It's just a cam made for bottom end torque and gas mileage. Sorry I don't have a recommendation, but I would be interested in hearing what the others in this community might recommend.
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