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Thread: Stay with 258 or go to SBC 350?

  1. #1
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    Army Stay with 258 or go to SBC 350?

    I have a 1986 CJ7 with a 258 inside. I have recently gone with a black Mountain 4inch suspension lift and upgraded to 33s. My transmission grinds on 3rd and 4th so I'll need to fix that and rebuilt the Dana 300 case. I bought the old girl used so I dont know how many actual miles the drive train has on it, all I know is the engine will need to be replaced.

    I plan on going with larger axles dana60 up front and 14bolt full floater in the back. Would it make more sense to go to a SBC 350 or just rebuild the 258 and pud mods on the engine for more power? I understand the easier path would be to rebuild the 258 with mods to get the HP. And a 350 swap would be pricier. Let me know your thoughts. I'm all ears.

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    Welcome to MJ. Considering the other upgrades you are planning I'd say go with the 350, but depending on which tranny you have now, you may want to upgrade that also instead of fixing the one you have.

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    Train Wreck mavdog32's Avatar
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    350 Isnt a bad swap if its carb. Its motor mounts and an adapter plate. Otherwise there are ECU's, wiring, etc. I also think if you go LT/LS its a new radiator too. There s a ton of info out there for this, especially on jeepforum and pirate. Spend a lot of time reading before doing the swap

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    Senior Member HillBillE's Avatar
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    Depends on what your final goal is for the rig.

    The 258 has plenty of torque for wheeling rocks and trails.

    If you want to spin the tires in the mud, or be able to cruise all day at 70+, then a V8 swap would be in order.

    With the correct gearing, even a 4 popper has the torque needed for most off road.

    The 258 has lots of torque, but has a red line of about 4200 RPM's on a fresh motor, if you want it to live for a while.

    There are some nice turn key V8's out there, even ones with EFI that come with their own ECU.

    Doing a carbed 350 isn't bad, stuck one in my CJ for a few years, but couldn't keep a trans behind it

    Take away: If you want to run mud, do a lot of deep snow wheeling, or plan on driving the highway to/from wheeling, then go with a V8

    If you plan on running rocks, trails, etc. The 258 has plenty of torque for that, and with some simple upgrades like the Nutter Bypass and an MC2100 carb, it'll run and wheel just fine.


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    Senior Member HillBillE's Avatar
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    Oh yeah....Welcome to MJ!! Lets see some pics of that CJ!


    As long as the people remain armed,
    government knows that it cannot rule over the people by force.
    Those who stand in defiance of unconstitutional laws
    do so out of duty, honor, oath and love of country.


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    Apathetic Sociopath MadOgre's Avatar
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    With the amount of mods and weight you're adding, I'd say go with the 350, but don't forget the HD 5 speed.

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    Senior Member SavageSun4x4's Avatar
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    Quote Originally Posted by HillBillE View Post
    Depends on what your final goal is for the rig.

    The 258 has plenty of torque for wheeling rocks and trails.

    If you want to spin the tires in the mud, or be able to cruise all day at 70+, then a V8 swap would be in order.

    With the correct gearing, even a 4 popper has the torque needed for most off road.

    The 258 has lots of torque, but has a red line of about 4200 RPM's on a fresh motor, if you want it to live for a while.

    There are some nice turn key V8's out there, even ones with EFI that come with their own ECU.

    Doing a carbed 350 isn't bad, stuck one in my CJ for a few years, but couldn't keep a trans behind it

    Take away: If you want to run mud, do a lot of deep snow wheeling, or plan on driving the highway to/from wheeling, then go with a V8

    If you plan on running rocks, trails, etc. The 258 has plenty of torque for that, and with some simple upgrades like the Nutter Bypass and an MC2100 carb, it'll run and wheel just fine.
    What he said X2!!!!!!!!!!!!!!!!!!!!!!!!!!
    Don

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC

    www.savagesun4x4.com

  8. #8
    Member CJ7nvrstk's Avatar
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    Welcome to MJ.

    Have you thought about an AMC V-8? Is a direct bolt in with stock parts available from junk yards. Tranny might be an issue with you though. If you have the T176 4 speed that would hold. BTW, you would have lots of choices. 290, 304, 343, 360, 390, 401. All share the same block. Now you generally won't built as much HP with an AMC V-8 as compared to a SBC and there aren't as many performance parts available but let me tell you a properly built AMC V-8 will build you tons of power. I have a built 360 in my CJ and power is not my problem at all. Putting that power to the ground effectively is. These 37" military take offs don't quite cut it.

    BTW, my CJ started life with a 4, then I swapped in the 258, then my first 360 and am now on my 2nd so been that done that thing. I have raced it quite a bit (sand drags) and have won some money with it. The AMC route is the way to go IMHO. Feel free to let me know if you have any questions.

    BTW, noticed soft sand wasn't mentioned above and with that soft sand you want lots of HP/torque that only a V-8 will give you.
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  9. #9
    Senior Member SavageSun4x4's Avatar
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    Quote Originally Posted by CJ7nvrstk View Post

    BTW, noticed soft sand wasn't mentioned above and with that soft sand you want lots of HP/torque that only a V-8 will give you.
    Couple of key points made here. The old AMC is certainly not a bad choice, does lack the plethora of goodies that are found in the SBC world, but still far from a bad choice.

    But the key point is that no matter what route you go its rare any PROPERLY built Jeep has an issues with lack of power WHILE off roading. Getting down the highway can often be a whole 'nother story. Start spinning 37> mounted on beadlocks and a whole bunch of armor and suddenly that trip to Moab is a two day drive rather than a one day. My rig coming out the chute weighed in around 3400 lbs, in trail trim I was pushing 5000. The 4.0 never let me down on any trail, but life on the highway was not fun till I added my supercharger.

    If you are going to do the wrenching yourself and YOU LIKE building the engine then HANDS DOWN there is only one choice for the builder in you and that is the Chevy, 350, 290 HP. You can buy them direct from GM with warranty for on the cheap. Its great HP/toque and a near bulletproof engine. Then there is the PARTS BIN be it GM or outside and that engine, heads, block and internals will juice well into the 400 hp/400 torque range for few dollars and you can have a lot of fun getting there.

    Soft sand: The world of off roading is a varied one and be it rocks on soft sand you rig need to be built to meet the challenge each brings. Sand is high HP and RPM, rocks are the low and slow of torque at idle and we don't much care if it even makes hp. Its engine, transfer case, tansmission, axle ratio and tires. Pick your poison and built to it, just remember that building your jeep as if it were a leatherman tool will only give you a jeep like a leatherman tool, does nothing well, but does do a whole lot good...
    Don

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC

    www.savagesun4x4.com

  10. #10
    Member CJ7nvrstk's Avatar
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    Quote Originally Posted by SavageSun4x4 View Post
    Pick your poison and built to it, just remember that building your jeep as if it were a leatherman tool will only give you a jeep like a leatherman tool, does nothing well, but does do a whole lot good...
    Not entirely true. For example...

    A CJ with a 258 will do quite well when, geared properly, in the rocks. That same Jeep though will be not so hot at all when it comes to thick mud, soft sand, or cruising the highway at 70+.

    On the other hand, take my CJ for instance. AMC 360 (which can be put in for considerably cheaper than a SBC but won't make quite as much power generally) T-18, D300, 4.88s. With the gearing set up this has, it will crawl with the best of em but still haul A$$ in the soft stuff and has plenty of power for the deep mud. In other words, this set up does it all. You will never get that out of any 6 banger.

    So, go V-8 and you can have your cake and eat it too, when properly geared. My CJ does beyond well or good. It does great!

    So ya, do the V-8. Be it SBC or whatever you choose.
    11 JKU

    85 CJ-7

    Glenn & Laura

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