258 rebuild or 302 conversion advice.

josh m

Well-Known Member
Joined
Mar 17, 2013
I'm looking for advice for my 8
I've got a 84 cj8 and I'm trying to get a game plan together for it. I've had it for 6 years, I'm not interested in turning it into a trail rig, just around town cruiser and occasional trail/snow driving. Want it to be more highway friendly.
Currently it's got 110k miles on the 258, 2100 motor craft carb, hei, 3.55 gears and 31-10.50 tires. It's started to develop a little piston slap noise. Possibly needs timing chain replaced. Timing jumps around. Leaks oil, needs intake/exhaust gasket, blablabla. 258 shit.
My question is should I go 302 or rebuild the 258. If I do all the stuff to the L6 I'll still have a low revving inline 6 that's not highway friendly.
The sbf seems like a good option as I have the t176 tranny, all I'd need is motormounts, frankinclutch, exhaust, and a 302.
Fuel injection isn't a option, whatever I do it'll be carbed. It's a 84. I'm not in a hurry to do this as it's running and driving but I could start collecting parts for this so it won't be such a big bill when I do it.
Any suggestions are appreciated.


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Build a stroker with your 258 parts, I see you want to keep a carb, but early 4.0 fuel injection is hard to beat on the street.

Most stock v8 swaps have the same rpm range as the i6.

I'm almost positive keeping the i6 would be cheaper than a v8 swap.
 
I've thought about doing a stroker. My main concern about keeping the 6 is that it sucks on the highway. Been driving back and forth to Raleigh from Burlington this week Bc snow. 3000 rpm for 45 minutes. I feel like I'm gonna blow it it. There are a few 258s for sale in the swap meet section. I've looked at em a couple of times.
To any of y'all running strokers, does a hr at 3k bug you? Or am I just being to sensitive? Lol


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Swapping a v8 may not bring the RPMs down like you think, unless you swap an overdrive transmission in at the same time.
 
strange1 said:
Swapping a v8 may not bring the RPMs down like you think, unless you swap an overdrive transmission in at the same time.
Click to expand...

I agree. I wasn't thinking it would drop rpms. The t176 is a strange transmission for a jeep. It doesn't have a overdrive or a low first gear. It's kind of the worst of both worlds. If you get it geared to work well around town it'll scream on the highway. I had the original 2.73 or 2.72 gears in it and 31s it was great on the highway. I drove it to Hilton head one summer and got low 20s in fuel mileage. It sucked getting it moving from a stand still. The reason I'm considering the 302 is because it lives better at higher Rpms, and it's bolts directly to my bell housing. Although it's not gonna have nearly the low end that the 6 has.
 
258 is a torquey little bastard but I'd rather have the 302, no real reason other than I just like it better, both good engines.
 
All the 4pointwhatever love is heartwarming. I'll look into the ax15 to dana300 kit.


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Honestly find a entire XJ for a donor.

Swap the 4.0 and injection in, use your 258 parts to rebuild it and stroke it, and done.

Swap the ax15 in it, just need a clocking ring to bolt up the dana 300 to it.

Hit up 4Wheelsupply on here for the clocking ring.

That all said, I'd run my stroker at 3k all day with no worry. The stock cams in the 258 and 4.0 start falling off at 3k and are done at 4K.

If you want an engine that will be happy at higher Rpms, get a Chevy 4.8,5.3,6.0 etc. They will run all day 12 hours at 3k rpms.

It's much simpler to swap trans or just get larger tires though.
 
I have a 302 swapped yj, new to me. So I got currious and compared some stock numbers. I've owned 4.0 Cherokees and a much older 304 CJ. Of the three the Cherokees this far pulled better and used less gas. Given the CJ was 3 speed best on the bottom end. The 4.0 was just strong in mid to low range. The 302 seems sorta blah. It's a truck engine so it pulls and has different characteristics of the HO cousin.
So back to the stock numbers...like 10hp or so. Not near the bottom end.
Now a built 302....another ball game. But it will still be higher pulling rpm.
 
I've had a couple of xjs that seemed happier at higher rpms, i really don't want anything fuel injected. It just seems wrong to me to put that in a scrambler. I think I'd kill the value of the car if I "overly modify" it. Guess I could build a well balanced stroker and find a duel Weber intake and still keep it old school. I hear what your saying WW the 302 will be great at higher speeds and blah around town.


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josh m said:
I agree. I wasn't thinking it would drop rpms. The t176 is a strange transmission for a jeep. It doesn't have a overdrive or a low first gear. It's kind of the worst of both worlds. If you get it geared to work well around town it'll scream on the highway. I had the original 2.73 or 2.72 gears in it and 31s it was great on the highway. I drove it to Hilton head one summer and got low 20s in fuel mileage. It sucked getting it moving from a stand still. The reason I'm considering the 302 is because it lives better at higher Rpms, and it's bolts directly to my bell housing. Although it's not gonna have nearly the low end that the 6 has.
Click to expand...
I might be understanding wrong but the 258 and sbf don't share a bolt pattern. You can swap bell housings on the t176 and adapt it to a ford. Same goes for most other trans also.

As said, i would fix the 258, upgrade the cam atleast and find an OD trans such as ax-15.
 
Or buy the 258 and 4.0 I have for sale, build the stroker while still driving the scrambler and just swap it out.

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I haven't pulled the head on it yet.
Would probably be bored for a stroker so they'd mill out.
I just dropped the price and can deliver as well...

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I'm confused. The 4.0 comes with head? What year did it come out of?


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Sent him a message. If it includes the head I may do it. I was thinking "short block " = no head


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josh m said:
I'm confused. The 4.0 comes with head? What year did it come out of?


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Click to expand...
I'm keeping the 4.0 head as of now. Could be persuaded to leave it on for the original price.
The 4.0 is from a 93 Cherokee.
4.0 is from an 84 cj7

Haven't gotten any new messages.

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Last edited:
justjeepin86 said:
I know you said you didn't want fuel injection, but another thing to consider if you were going to us a 4.0. It will walk the dog on a stock 4.2. You wouldn't really need a stroker to tell a huge difference, IMO.
Click to expand...
Goes back to the hp of 302 to a 4.0 very equal with a very biased torq curve for the 4.0
 
Well if I do the stroker and get everything balanced well to spin a little faster. I've read that I can bolt up the 4.2 intake to the 4.0 head with a little modifying. Maybe upgrade to a offy duel plane intake and 4.0 exhaust manifold. It sounds like it'll breath better at higher rpms. Do y'all agree that this is a sound plan?


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I actually have a factory 4.0 header as well.

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