258 performance mods or upgrades - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 09-23-2002, 11:31 PM
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258 performance mods or upgrades

Just wanted to know what performance mods are out there for the 258 engine? My brother just bought a 1983 CJ7 (made decision based on your all input). He will probably have the engine reman. or rebuilt. He thinks the carb system need a lot of work, so he might want to buy a new carb/intake system.

Start with the best bang for your buck mods. I suggested a K&N fliter system & headers to start.

Since he might rebuild the engine, he wants to know what all is recommended or available for the six.

Should he change years on the six or was 1983 a good year.

He's more interested in torque than HP, but HP is O.K. He not looking for a huge increase in numbers (200 hp is probably max)

He is really concerned with carb and intake manifold. Whats a good set up? He might consider an FI system but they are very expensive. Any suggestions.

Any other suggestions are welcome. Keep in mind he doesn't want to take out a loan to pay for these upgrades.


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post #2 of (permalink) Old 09-24-2002, 07:58 AM
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Re: 258 performance mods or upgrades

I was recently forced to rebuild my 258, and I performed the following with excellent results. My engine was a dog, but now it pulls HARD.

1. Bored block .060 over taking displacement up to around a 4.3L, installed new pistons
2. Machined the head, 3-way valve job all to bring up compression
3. Cleaned the entire engine in the tank, ridding it of about 150,000 miles of built up chud, installed new oil pump and full gasket kit
4. Installed Crane Torque Cam (1500-4500RPM power curve), plenty of bang for the buck at around $120 bucks
5. Added Holley 350 2-barrel Carb to the factory intake which I polished myself. I felt that the Holley was a better deal than the Weber, and was WAY easier to find parts for.
6. Finally bolted on a Pacesetter header so she could breath a little better (not too many choices on a header for me being that i have a YJ).

The finished product is night and day from where I started. Before I had problems stalling on an incline or deep sand, now I just blast through it. Pulling out into traffic the other day I had to stomp on it, and actually started roasting my swampers. Oops, but it made me appreciate how well it had come together. Good luck on the engine!

post #3 of (permalink) Old 09-24-2002, 07:59 AM
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Re: 258 performance mods or upgrades

My best three suggestions...
1. Find a 1975-1980 crankshaft, casting # 3214723. These have much heavier counterweights.
2. Install a 4.0 head.
3. Install a 1991+ 4.0's fuel injection or an MPI kit.

... or look for a complete 1991+ 4.0 engine and swap the whole thing in.

Best of both worlds ... Use the afore mentioned crank to make a stroker out of a 4.0 HO engine assembly.

These and more tips are on my Jeep site (link below)
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post #4 of (permalink) Old 09-24-2002, 08:50 AM
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Re: 258 performance mods or upgrades

Some other things that can be done are the TR/TFI Upgrade and Nutter bypass. Do a search here and on Jeep unlimited BBS and you should find info on those. Haven't gotten around to doing them yet, but I hear pretty good things about them.
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post #5 of (permalink) Old 09-24-2002, 10:05 AM
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Re: 258 performance mods or upgrades

I found a new Weber carb on ebay for $275.
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post #6 of (permalink) Old 09-24-2002, 04:28 PM
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Re: 258 performance mods or upgrades

A 258 can be modifed, i would keep the mods pretty simple because once you start adding up the $$ to modify a 258 you could just as easily swap in a 4.0 or vortec 350. I would say keep the mods simple, do things like the tr upgrade, mc 2100 carb, and then just keep it in working order.

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post #7 of (permalink) Old 09-24-2002, 05:52 PM
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Re: 258 performance mods or upgrades

I have to agree with Barrelroll.
Several issues to look at...first, you have to be carefull about what hardware you put on. If your state does not have smog testing/inspections now, most likely it will soon. All those guys out there that pulled off all their emissions equipement are going to be parking their rigs when they can't pass inspection.
Cams - Bigger cam means less low end vaccum which hurts the rock crawling.
Carbs - They flood on hills...FI is really the only way to go.

I have rebuilt 2 258's and one 4.0. On average, I spent $1200-$1600 per engine..but that was everything...

A Mopar FI retrofit is about $2000.

8 Of the top 10 rock crawlers are running automatics (please, don't bash me on this one).

When you look at the big picture.... I honestly think that when faced with a full rebuild, swaping in a chevy 350 w/Auto tranny out of a Caprice or PU is a cost effective solution. If you shop the auctions, you can get a wrecked doner with a good engine and tranny. Strip the engine, tranny and electronics and with a little (ok, a lot) of work, you end up with a fuel injected jeep. A buddy of mine just did it to his Wrangler. All told, he had about $4000 in his...but that included $1700 for just the Corvett LT1 engine with less than 30K miles on it. He also farmed out a lot of the custom work. I'm hearing that it cost about $1200 over the cost of the engine and tranny (Transfer case adapter is the most expensive part at about $750). In my case, I have no doubt I can sell my 258 with less than 15K miles and matching rebuilt T5 for at least $1500 to cover most of the costs.

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