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Unread 07-28-2011, 06:21 PM   #1
ctappan94
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AMC 360 vs 258

Hi, I have the 258 motor in my cj7 at the moment but I'm wondering if I should swap it for the v8. I like the way the v8 sounds more, and it would give me more peace of mind in terms of reliability because theoretically, 8 cylinders versus 6 means less work per cylinder. Assuming that price would not be the biggest issue, how does fuel economy compare? And what can I do in terms of mods to make these motors a bit more powerful?? And how do they compare in terms of power when stock?? Just any comments anyone has on these two engines would be greatly appreciated!!!

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Unread 07-28-2011, 07:02 PM   #2
Jeep-N-0311
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(Dating back to about ... '76) I've always had (or transplanted in...) 258's in CJ5's & CJ7's; while I had friends with both (Jeep) 8-cyl's, 350's, etc. The only exception was a '65 CJ-5a, that came with a 134 F-head (I didn't switch a thing on that drive train). The only things that I ever really noticed about the 8-cyl's was the ability to hit higher hiway speed, in order to stop at more gas stations. The CJ can be a (semi) powerful machine with a 4-banger, and that straight-6 is one of the best basic designs out there. If you look at the Toyota FJ's (at about 1000 lbs more), they settled in to a similar 258 straight-6 design ("2F") for decades - check out one of their forums (i.e. - "ih8mud.com"), and most of the 2F motor people swear by them. If you have a good set-up underneath (Carb, Dissy, tranny, rears), then, unless you're planning on becoming hard-core, you probably will have more machine than need.

On each of my last 3 Jeeps, I thought really long and hard about getting a (Jeep) V-8. Just couldn't come up with a good enough reason.

If you want dual exhaust, and "sounds", I guess that you could switch over, but, before you do, you might want to find one of the old OEM 20 Gal tanks, first.

Just my $0.02
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Unread 07-29-2011, 11:16 AM   #3
ctappan94
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Well its going to be a daily driver, taken offroad on weekends and some week nights only. I need the ability to hit 85 (though id never do that in it), I just dont want to be red lining at 70 something... It would save me some money with keeping my 6... but is there anyway to make it more powerful besides the 4.0 head, and a carb, intake manifold? It's got 36" right now and I plan on keeping them, too. Do you know if theres any cams or exhausts that will really give it that deep grunt??
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Unread 07-29-2011, 11:55 AM   #4
TxJeeper20
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well mabye regear the axles or trade it out for an overdrive tranny if ur happy with the 6 , I am going with a TBI 350 for my jeep a bit never fuel system and it self diagnosis the engine lol I want some balls and highway speed to my jeep with the new engine and tranny combo i should get it and MPG will be around the same or better with more power
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Unread 07-29-2011, 01:29 PM   #5
alljagged24
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I could wire in a programmer off ebay (like 19.99) they guarantee 60 hp gains for any vehicle .....generic programmer


On a more serious note, my 258 is plenty too strong in my opion with the mods u listed and a dui dizzy and a fresh build
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Unread 07-29-2011, 01:38 PM   #6
79jeepincj7
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I'd always go for the V8.. I love the sound, the power, everything about them. If driven nicely your gas millage wont be that much worse then the I6. as for red lining ... that has nothing to do with the motor.. both rev pretty close. Thats all in your axle gearing and your trany you have.

To swap a 360 in its as simple as just ordering the new mounts and bolting them on the frame. May need a 3 core radiator if you dont have one already. And you'll have to do something about the exhaust and the fuel lines on the other side of the motor.
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Unread 07-29-2011, 01:53 PM   #7
chainz
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I agree with jeepinc I know a lot of people stand by the inline 6 but to me it is not enough when you put a lift and tires on it and then need to get out of a mud hole even with re-gearing it is not as good as a V-8 to me. I think that a lot people like a 6 until they try an 8 and then they never look back, i didn't.
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Unread 07-29-2011, 03:01 PM   #8
CoryA
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Well add up the price of the mods you'd do to the 258 and figure how much hp you'd have then add up the price of a 360 swap and figure the up you'd have that was a big determining factor for me.
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Unread 07-29-2011, 03:14 PM   #9
kickingprop
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I think you'll find that a well tuned, well geared 258 will do everything you ask of it in terms of power and reliability. The one thing it wont give you is that V8 sound.

The 360 will give you more oooomph but it also won't be passing very many gas stations, whereas plenty of people get 20mpg highway out of their 258's.

Having said all that, I do sometimes miss the simplicity of my old 258.
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Unread 07-29-2011, 06:32 PM   #10
96-XJ
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Do you really use a lifted CJ as a DD, and 80mph!!!? Back pains...? Other wise who cares about the MPG, the thing is a beast!

i just bought a 77 AMC360 with 77k original for $200 and it runs great!
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Unread 07-30-2011, 04:56 PM   #11
ctappan94
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Damn! I paid a thousand for mine and that was non running!!! and I wish it had the 360.... and mine has 100k but yeah Im selling my 2011 VW gti so this will be my DD
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Unread 07-30-2011, 10:16 PM   #12
TxJeeper20
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Quote:
Originally Posted by ctappan94 View Post
Im selling my 2011 VW gti so this will be my DD
you love your jeep/and or trust it lol I love mine to but I want a newr car incase it conks out on me even tho im having it restoered dont no if id trust it enough to be DD
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Unread 07-30-2011, 10:49 PM   #13
Pacfanweb
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Quote:
Originally Posted by chainz View Post
I agree with jeepinc I know a lot of people stand by the inline 6 but to me it is not enough when you put a lift and tires on it and then need to get out of a mud hole even with re-gearing it is not as good as a V-8 to me. I think that a lot people like a 6 until they try an 8 and then they never look back, i didn't.
100% agree. I've had a bunch of CJ's with 258's and wished every one of them had a V-8 at the time.

Current CJ that I'm building has a 406 SBC.
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Unread 07-31-2011, 12:56 AM   #14
ctappan94
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Im thinking about a ford 351 windsor for mine.. I feel like the 258 is underpowered .. I even had a dream about it last night (call it an addiction!!) the 360's oiling problem... i didnt want to deal with that.. I know that the value will be lowered but I think ill take the ford.. :P
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Unread 07-31-2011, 09:04 AM   #15
duckbone
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I just pulled a 351 clevor out of mine to swap in a 401.
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258 , 360 , 4.2l , 5.9l , amc

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