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Old 10-24-2010, 09:37 PM   #1
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Hey I have a CJ7 with a stock 258 I6 and was wondering if there was a way to get more horsepower without putting a totally new engine in it.

Also I plan to put headers and dual exhausts on it. Will this help?

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Old 10-25-2010, 09:51 AM   #2
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Best older I-6 upgrade is HEI IMHO.

Got a lot more power and almost double the mileage on my DJ...

Is it the '80s "computerified" 258 or the 70's no computer 258? I think they added an electronic ignition in 1980 (don't quote me though)

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Old 10-25-2010, 10:02 AM   #3
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Nitrous!
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Old 10-25-2010, 06:26 PM   #4
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I don't think it is electronic but im pretty sure it is an 85 engine.
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Old 10-25-2010, 07:27 PM   #5
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I don't think it is electronic but im pretty sure it is an 85 engine.
You're the second guy and the last couple days to ask how to UP their horsepower in an older Jeep. I envy you guys with the CJ's because if I had bought that damn used 70's Golden Eagle back in 85' it would be a monster by now. The only real option us JK owners have is to buy a damn RIPP charger. But anyone with a straight six can stroke the hell out of their engine.

Anyways, you need to find a damn good machine shop in your town and get your 258 balanced and blueprinted. You can ask around to see who's rep stands out the best. If there's a NAPA auto parts store in your town that will be the best place to start. If not, then try a reputable auto body store that sells professional grade equipment, auto paint etc. Then again you may already know a good machine shop in your area.

Basically what they'll do polish and soak the head and block, shave out any imperfections, and replace any worn out parts. There's more to it than that but I'm not going to write the equivalent of a novel to explain it. I'm sure you can get anywhere from 15 to 30 horsepower and torque, maybe more. It'll probably cost you between 900 to 1200 bucks.
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Old 10-25-2010, 09:09 PM   #6
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Can getting a high performance carburetor give me more power too? Or better performance.
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Old 10-26-2010, 12:05 PM   #7
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Can getting a high performance carburetor give me more power too? Or better performance.
That's a whole different category. If you wanna mess with the carb too, then you also have to think about buying a better intake. Holley carbs are great for street performance but not so much for off-road. Weber is better for off-road. I've heard that offenhauser is a good intake manifold to go with. You're definitely going to need a carb with an electric choke. A two barrel Weber would probably be the best way to go.
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Old 10-26-2010, 08:49 PM   #8
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Old 10-26-2010, 09:07 PM   #9
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That's a whole different category. If you wanna mess with the carb too, then you also have to think about buying a better intake. Holley carbs are great for street performance but not so much for off-road. Weber is better for off-road. I've heard that offenhauser is a good intake manifold to go with. You're definitely going to need a carb with an electric choke. A two barrel Weber would probably be the best way to go.
Will this carburetor work with a 258 i6 though?
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Old 10-26-2010, 09:13 PM   #10
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What gears are you running?
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Old 10-27-2010, 07:11 AM   #11
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Will this carburetor work with a 258 i6 though?

The moderator was right. Or at least he/she brought up the next appropriate thing to do to your Jeep, which poses several more questions. You're going to have to run different gearing when you mess with your carburetor and intake. The next question is this:What size tires are you running? Are you currently running on that stock AMC 20 rear end or have you changed over already? If you're running that stock rear end, a beefed up 258 will eat it up and you'll be sitting in the woods wishing your roadside service company had a 4WD flatbed.

The cheapest and most effective way to go is to switch to a stronger one piece AMC 20 replacement axle, which will cost around 300 to 400 bucks. Otherwise, you could switch out the whole rear end and get a Dana 35 or a Dana 44, which costs between 1200 to 2000 bucks. Hell, it would be cheaper to invest in some jack stands and a few tools and rebuild your AMC 20 yourself.
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Old 10-27-2010, 10:21 AM   #12
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I've heard that offenhauser is a good intake manifold to go with. You're definitely going to need a carb with an electric choke.
I got an Offy... No complaints whatsoever If you want a 4BBL, it's the ONLY option AFAIK.

I have a manual choke on my '71... it was electric, but it got to be such a PITA that I decided to mod it via hammer

'85 should have a PITA ignition controller in it... if it were mine, I'd still go HEI and all that garbage would get yanked, but google around and see what you can do with what you have, it's a decent starting point when you compare it to a points distro, and there might be a summit racing controller or equivalent that will work wonders with what you have...
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Old 10-27-2010, 12:17 PM   #13
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I got an Offy... No complaints whatsoever If you want a 4BBL, it's the ONLY option AFAIK.

I have a manual choke on my '71... it was electric, but it got to be such a PITA that I decided to mod it via hammer

'85 should have a PITA ignition controller in it... if it were mine, I'd still go HEI and all that garbage would get yanked, but google around and see what you can do with what you have, it's a decent starting point when you compare it to a points distro, and there might be a summit racing controller or equivalent that will work wonders with what you have...
1971--Jeezus. Thanks for the refresher. But if he's getting a new carb don't you think he should get a 2 barrel Weber (electric choke) to go with that HEI distributor? I purposefully stayed away from the 4 barrel recommendation cause' he might not be pushing high enough RPMs to open up those other two barrels.
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Old 10-27-2010, 01:43 PM   #14
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Thanks and I will take everything into consideration. I'm in highschool and don't know a whole lot besides what I'm reading and what You guys r telling me.
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Old 10-27-2010, 04:29 PM   #15
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1971--Jeezus. Thanks for the refresher. But if he's getting a new carb don't you think he should get a 2 barrel Weber (electric choke) to go with that HEI distributor? I purposefully stayed away from the 4 barrel recommendation cause' he might not be pushing high enough RPMs to open up those other two barrels.
LOL... didn't realize it read that way NO, I would not recommend a 4BBL unless you KNOW you can use it. I went with one for simplicity's sake (I'm a reformed hot rodder, I can rebuild a 4BBl in my sleep), and the secondaries open very rarely, but a 258 can and will open em if it needs to (I actually have a 232, and if I drove like an idiot, they'd open up all the time...)

I was just saying that Offy makes the only 4 model intake that I know of...
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Old 10-27-2010, 04:36 PM   #16
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LOL... didn't realize it read that way NO, I would not recommend a 4BBL unless you KNOW you can use it. I went with one for simplicity's sake (I'm a reformed hot rodder, I can rebuild a 4BBl in my sleep), and the secondaries open very rarely, but a 258 can and will open em if it needs to (I actually have a 232, and if I drove like an idiot, they'd open up all the time...)

I was just saying that Offy makes the only 4 model intake that I know of...


Serious question: Did you open the 4barrel up on the street or off-road?

I'm asking cause' if you opened her up off-road and you wasn't in a tractor pull competition what were you doing? Must have been a hellified hill climb!
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Old 10-27-2010, 05:04 PM   #17
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Will this carburetor work with a 258 i6 though?
Okay, so it's like this: The first thing you need to do is to upgrade that rear end. Horsepower don't mean nothing if you can't put it to the ground. Cheapest way to get out of replacing your entire rear end is to get a stronger, one piece AMC 20.

If your CJ has the original 258 engine and original parts, then you currently have a Carter 1 barrel. Throw that 1 barrel in the garbage can (or make a paper weight out of it). You're going to get a 32/36 DGEV Weber with electric choke. You'll get worlds better performance as far as horsepower and better gas mileage.

You'll need an Offenhauser intake manifold to go with that Weber. That'll bump you up another few horsepower. Then get the engine balanced and blueprinted. That'll knock you up a few more horses. Then you get you an HEI distributor. Later on you need to think about a Header and a muffler so that little monster will poot better.

The original horsepower/torque numbers were 112HP/210Tq. After all that modification you'll probably be pushing 4.0L numbers or better.
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Old 10-27-2010, 06:44 PM   #18
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I have an AMC 20
Right now I think. If that's the same thing as a DANA 20 oh and would Detroit lockers help
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Old 10-28-2010, 06:41 AM   #19
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I have an AMC 20
Right now I think. If that's the same thing as a DANA 20 oh and would Detroit lockers help
A Detroit locker for an AMC 20 is around 700 bucks but you'll need front and rear lockers, so that's going to be anywhere from 1800 to 2000 bucks because there's varying grades of lockers. But a lot of modification is related. If you're thinking about lockers, then you have to think about replacing the drive shafts especially on a vehicle that's 25 years old. You also need to examine your old AMC 20 housing for leaks. Are the tubes bent or dented anywhere that would cause an obstruction for the axle rods?
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Old 10-28-2010, 08:38 AM   #20
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Well my AMC 20 is in good shape from what I know. Everything is as it should be.
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Old 10-28-2010, 11:37 AM   #21
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Serious question: Did you open the 4barrel up on the street or off-road?

I'm asking cause' if you opened her up off-road and you wasn't in a tractor pull competition what were you doing? Must have been a hellified hill climb!
both actually... the DJ is still 2WD, it climbs hills, it launches off sand dunes, it plays in the mud, but off road, if it slows down, it's tow strap time
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Old 10-28-2010, 04:37 PM   #22
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Well my AMC 20 is in good shape from what I know. Everything is as it should be.
That's good. Unless you have cash to burn I'd hold off on the Detroit lockers for now. Just stick to the aforementioned. Any well-equipped Jeep can handle all but the absolute worst conditions. And after those mods you'll wonder why you even asked about a Detroit locker. As long as your rear end is solid and you have moderately aggressive tire tread you should be fine.
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Old 10-28-2010, 04:39 PM   #23
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both actually... the DJ is still 2WD, it climbs hills, it launches off sand dunes, it plays in the mud, but off road, if it slows down, it's tow strap time
Yeah, flooding issues with that massive piece of meat sitting on top of your intake manifold. But damn that's a nice toy to have, though!
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Old 10-29-2010, 06:35 AM   #24
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Old 10-30-2010, 11:36 AM   #25
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My AMC 20
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Old 10-30-2010, 01:52 PM   #26
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My AMC 20
Yep. It's leaking.

You'll need a one piece AMC 20 axle kit ($342):




For good measure get yourself a heavy duty differential cover ($76):



Floor jack ($104):



Jack stands ($35 Ea.)

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Old 10-30-2010, 10:33 PM   #27
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Yeah sorry I forgot to mention its not leaking from there but there's some run off grease or oil that used to leak and it would trickle down to the "pumpkin" and drip off.
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Old 10-30-2010, 10:48 PM   #28
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Yeah sorry I forgot to mention its not leaking from there but there's some run off grease or oil that used to leak and it would trickle down to the "pumpkin" and drip off.
Nevertheless, if you plan on modifying the engine with the aforementioned upgrades the power increase is going to be such that an axle that was already considered sub par 25 years ago will snap like a dry twig over time if not on the first ride. Here's two examples of what a broken axle looks like:



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Old 10-31-2010, 09:19 PM   #29
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Sorry I ask so many questions but if I just stick with putting headers and dual exhausts for now will that really effect anything besides the loudness and the 3 cylinder per exhaust pipe thing.
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Old 11-01-2010, 12:09 PM   #30
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Sorry I ask so many questions but if I just stick with putting headers and dual exhausts for now will that really effect anything besides the loudness and the 3 cylinder per exhaust pipe thing.
You have to ask questions in order to find out what you need to know.

For about $250.00 you can get a Hedman six-into-two header:



You'll get about 10 to 15 extra horsepower.

Header paint: $12.00


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