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Old 06-10-2019, 07:36 PM   #1 (permalink)
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power train opinions CJ7 GM vs AMC

I am looking to replace the 258/t150/d20 thats currently in my CJ7 with V8 power to match my full width 3/4ton axles and I have found two options semi locally

1. 1984 K20 350/sm465/np208 (i believe based on talking to the owner)-I would get this whole truck, pull the drive train and scrap the unneeded parts. Long term would be adding a Np205/ORD magnum box or 231/241 crawlbox of some sort, but would have to source some extra parts. I am much more comfortable working with the GM stuff experience wise.

2. 304/th400/D20- pulled from a CJ5 all in working order with some extra "hot rod parts" I know this would be a very direct swap and have me up and running much quicker than the GM drive train, but I know there are limited options with AMC stuff (Engines and Trans) plus added expense for AMC stuff. My goal with this swap would be to run a 231/241 crawl box directly to the trans (27 spline output th400) so my configuration would look like this trans-crawlbox-stock D20 adapter-D20 (with bronco low gears)

length is not an issue my Jeep sits at 108" wheel base (frame stretch plus flipped Xj springs)
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Old 06-10-2019, 08:41 PM   #2 (permalink)
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Go GM. Parts way easier to find and more cost effective. 304 underpowered gutless wonder, don’t matter what you do to it.
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Old 06-10-2019, 09:29 PM   #3 (permalink)
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thats what I was thinking, the sm465 inspires much more confidence as compared to a th400
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Old 06-11-2019, 02:22 AM   #4 (permalink)
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Depends on what you want to do....GM parts are cheap and plentiful...The 20 outputs will be stressed with all of that gear reduction depending on axles and tires,but it is a decent case for the size of the jeep chassis. Seen a lot of GM cases installed hanging way low below the frame so plan on clocking those...GM you will need to fab or buy all of your mounts and a conversion radiator...

I have an "all Jeep" Cj7...401, T18, D20. I like it. I might not do it again.....
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Old 06-11-2019, 06:07 AM   #5 (permalink)
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I am looking to replace the 258/t150/d20 thats currently in my CJ7 with V8 power to match my full width 3/4ton axles and I have found two options semi locally

1. 1984 K20 350/sm465/np208 (i believe based on talking to the owner)-I would get this whole truck, pull the drive train and scrap the unneeded parts. Long term would be adding a Np205/ORD magnum box or 231/241 crawlbox of some sort, but would have to source some extra parts. I am much more comfortable working with the GM stuff experience wise.
Forget the NP205. It's massive and doesn't fit well into a CJ7, especially with an ORD magnum box. You'll also have no room for a rear driveshaft with that combo. As for the 231/241, why ???? If it was me I'd go with the 350/SM465 and stick an Atlas II behind the SM465.

https://www.novak-adapt.com/catalog/...65-to/kit-463/

https://www.advanceadapters.com/prod...jeep-dana-300/

Those adapters will mate up an NP465 to a Jeep Dana 300 T-Case. All you need to do is buy the Atlas II to replace a Dana 300. This gives you the ability to "clock" the T-Case for more ground clearance.
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Old 06-11-2019, 07:53 AM   #6 (permalink)
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I was gonna say put a NP241C behind the the SM465, but by the time you are done you'll have 1K dollars into that, with a SYE (which is mandatory). A better option, which has already been suggested, is an Atlas II, for another thousand on top of what you'd have into a 241. If you don't have that extra thousand then a sye'd 241 will get the the job done, so long as you have a good skid under it to protect it. But save up the the money for an atlas and do it right once is your best option really.
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Old 06-11-2019, 07:59 AM   #7 (permalink)
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Get a $300 XJ and part it out. I mean you already got XJ springs so the swap will be simple

4.0, AW4, 300.
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Old 06-11-2019, 08:03 AM   #8 (permalink)
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Y'all are jumping too far ahead. It's a D44/10B front. An atlas is putting the cart before the horse.

You need to decide between auto or manual.
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Old 06-12-2019, 08:46 AM   #9 (permalink)
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Don't go auto trans on a pass drop front axle. Yeah, sure it can be made to work on a CJ, and is done all the time. I have one in mine. In order to do it I needed a 2 pc front ds which is not that big a deal in a CJ with hubs that unlock, but it's just a pain in the ass that can be avoided by using ANY manual trans. OR swap front axle to driver drop and run anything you want with no ds clearance issues.

Might as well swap to D60 if yur gonna get a driver drop axle. Might as well this. Might as well that. Might as well's can get out of control fast.

350/SM465/D300 is a great option. Been there, done that. NP241C great option (as mentioned b4). Been there done that. Hell even an NP231 is an OK option, if you always plan to keep the axles you have. Atlas II is and a good investment for the future, cause you know eventually you'll have links and won tons.
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Old 06-14-2019, 05:56 AM   #10 (permalink)
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Ill chime in as a dude with a CJ7 with a fuel injected cammed 304 T18 D300 with 4-1. mine rips down the road fine and wheels great. Anyone can swap a GM into a jeep. Nothings wrong with AMC engines, its just money man and the looks i get when people ask what engine is in it is worth it for me
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Old 06-14-2019, 06:36 AM   #11 (permalink)
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Ill chime in as a dude with a CJ7 with a fuel injected cammed 304 T18 D300 with 4-1. mine rips down the road fine and wheels great. Anyone can swap a GM into a jeep. Nothings wrong with AMC engines, its just money man and the looks i get when people ask what engine is in it is worth it for me
Same here but with a geared 20 and AA output on tons,no issues
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Old 06-14-2019, 09:36 AM   #12 (permalink)
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I'll chime in again as a dude with a 6.0 liter LS/4L80E/NP241C. For about the same amount of money as a TBI'd 350/SM465/D300, skip that and get a 5.3 LS/4L60E/NP231 or NP241C. The LS combo is light years ahead in terms of usable power/torque, reliability, parts availability, economically friendly for the long term, more tune-able, more drive-able and has best overall general usefulness. You want a power-train you can install and forget about other than routine oil/filter changes, you install a 5.3 LS. There's good reason LS swaps are annoyingly in your face everywhere you look. Economically it makes sense vs using the native AMC engine that came in your CJ, or even older GM technology. Good economics and Jeeps don't go together, but whatever.
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Old 06-14-2019, 10:55 AM   #13 (permalink)
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One of the new self tuning EFI throttle body units will cure most of the drivability and tuning issues with running an AMC powerplant.

AMC = A Mighty Car!
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Old 06-15-2019, 12:19 AM   #14 (permalink)
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Yeah but there's still the whole greezy AMC iron chunk under it eeeeewww get it off get it off.
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