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Old 12-23-2013, 02:54 PM   #1
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4.2 motor question

Im justing sitting here looking around, and was looking to see what a new 4.2 258 carbed 6 cylinder would cost if i wanted to buy new instead of rebuild. Also do they make performance parts for this motor? Headers, high rpm heads, intake manifolds for torque? Stroker kits? Wander if a turbo would go great? .....just curious cuz ive yet to find any if this sorta stuff....i guess ppl buy the 8.8s and drop 302s in the engine bay lol

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Old 12-23-2013, 06:02 PM   #2
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I'm afraid you are barking up the wrong tree if you are thinking any kind of major performance from a 4.2L. The motor was originally designed for torque, low end, nothing in the top end for speed or performance.

I have a "new" 4.2L in my 87. Built for low end torque. It has an Offenhauser performance intake on it with a Holley 390CFM carb. I built a custom 2.75" exhaust complete from front to back, to open it up and let it breathe. Custom built cold air intake and snorkel. HEI ignition system. Electric fan kit. All of these things add to the performance of the vehicle, but its still just a 6cyl.

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Old 12-23-2013, 06:12 PM   #3
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Yes torque is what im going for, thanx. Would you know were i can buy a new 258?
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Old 12-24-2013, 01:27 AM   #4
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If you want Torque and a strong mid to top range get the 4.6 or 4.7 stroker motor it's the best of both, if built right.
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Old 12-24-2013, 01:53 AM   #5
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check clifford for performance parts. if a stroker interests you go to jeep stroker forum and read up. there are lots of parts available for the 4.2.
I'm happy with the performance of mine but if your wanting a hot rod go with a V8
you aren't going to find a "new" 258 but many companies sell remanufactured motors, ATK is one.
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Old 12-24-2013, 10:12 AM   #6
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MD isn't too awful far from me. I have a good 96K mile 4.2 that needs a new home that would be a heck of a lot cheaper than a new one.
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Old 12-24-2013, 10:23 AM   #7
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daddyjeep, thanks but im not in the market to buy one just yet...just browsing and see what i can find...the popular motors like 350's and all ive never had a problem with finding for obvious reasons but seems like this inline 6 is.....wander why they dont make new blocks and all for them...ive got 137xxx miles on mine, and figured its just a matter of time of when ill have to overhaul the motor and that means, new rods, over sized pistons, bore the block to get all the scratches out and so on....
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Old 12-24-2013, 03:51 PM   #8
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Your motor still has lot of life left in it. These things run forever.
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Old 12-24-2013, 08:27 PM   #9
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In 1991 when AMC started putting 4.0's in the YJ they abandoned the 4.2 manufacturing all together. Used 4.2 motors are quite rare compared to the 4.0. #1 reason--they didn't make nearly as many. #2--they stopped making them almost 25 years ago and many have been scrapped. You can find remanufactured 4.2's but they are still quite expensive. Your core turn-in is about $400. On the other hand used 4.0 motors are much easier to find...I got mine off or CL for $250 w/98k miles in really good shape. The conversion process to fuel injection will cost some money (there are some really good write-ups on that. HESCO makes conversion kits). But for about the same $$$ as a reman 4.2 you can do a 4.0 and get the extra horsepower and better fuel economy...not to mention eliminating all the hassles of the carb.

There are guys that love their carbs and will argue different. I see a lot of value in what they talk about but I lean toward the FI.

There are also guys that will swap a 4.0 head on to a 4.2 block (lots of good threads out there on that too). Thought about going that direction too. Lots of extra horses and you can keep the carb. If my 4.2 was in better shape I may have ended up doing that instead?!

Anyhoo, keeping reading and researching. There is tons of info and many different approaches you can take to upgrading the motor...just gotta figure out what's best for you and the type of driving you'll be doing. Good luck!

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