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Amc 401 yj

6K views 32 replies 13 participants last post by  remmons 
#1 · (Edited)
In the process of doing an engine swap in an 90' YJ. I'm running 44" Super Swampers with 4.56 gears as of right now. I had an inline 6 but have purchased an AMC 401 to put in its place. I currently have the AX15 transmission and NP 231 transfer case but have the plan of replacing with a T19 transmission and Dana20 transfer case. What are all of the issues that I will run into and how do I go about fixing them?
 
#2 ·
The first thing that I can think of is your Dana 20 t case will be passenger side drop.
 
#5 ·
I dont know much about flipping transfer cases but I know it can be done. Check out Novak or Advance Adapters for the drivetrain adapters
 
#7 ·
I would think so. Or try to adapt the trans to a 241 to keep it driver drop.
 
#12 ·
not the best motor in the world, it can be built, but it's expensive to make any decent power from. a fuel injected 4.0 makes similar numbers stock vs stock.
for 44's i'd be looking for minimum 5.38 gearing, probably even higher with bigger axles. i really can't believe you're able to go anywhere that isn't pavement with 44's on a d44/60 combo too. that's a lot of tire.
 
#14 ·
there is nothing about an ax-15 np231 combo in front of 44"s that is going to last very long. especially after tossing in v-8 power. the ax-15 will give up the ghost first, i speak from experience.

44"s is alot of tire like rat said, there is no way on gods earth i would think anything numerically lower than 5:13's would even come close to keeping you in the power band for the older 401 amc motor.

i am merely going on speculation since i have no concrete evidence other than common sense to go on. it is pretty much a standard to go with 4:88's on 37"s, this is the only piece of data that i am basing my statement on.

i'm not even going to touch the axle debate, god kills a kitten every time someone argues axle/tire pairing on JF.
 
#15 ·
If your front D44 is a right hand drop, then you should have no problems with that set up. I would have to agree that the stock 401 v8 vs. injected 4.0 both produce nearly the same numbers, and both can make great motors if you're willing to invest in them.

But, my old hot-rod motto is "there's no replacement for displacement."
 
#17 ·
It's not set up for mud at this point, not sure if it will ever see mud. Ideally I'd like to put one tone Chevy axles underneath it and be able to use my T19 and Dana 20. As far as the AMC 401, it won't be seeing 5,000 RPMs. More so it it a vehicle for leisure, the occasional weekend cruise and a couple truck shows a year. As of right now, I'm going to drop in the 401with the AX15 and NP231 behind it. The Dana 44 (stock) front drive shaft not connected and Dana 60 (4.56) do not have matching gears as of right now but came across a Chevy Dana 44 and a Chevy 14 bolt with matching 4.10 gears but reading your responses, it doesn't sound like either way I go would be too wise.
 
#18 ·
With the 44 inch tires you are in 1 ton stuff by default. Be it shaft size or even braking ability. A Dana 60 with the common 30 spline shafts is nothing special.

The 401 is fine if that is what you have your heart set on. Just be aware that there are better choices.

44 inch tires
14 bolt
Dana 60 front or make a steering 14 bolt.
5 series gears
T350/400/4L80
SM 420/465/NV4500
NP 205
 
#19 ·
Mounting the AMC 401 is the least of my issues/worries, I have the motor mounts and know that it will fit, it's the transmission, transfer case, axels/gears and braking that I'm most curious about and all of you have given good insight as far as the direction I might want to go. I want a solid build that is different than what others have out there.
 
#20 ·
I want a solid build that is different than what others have out there.
If you read Novak's site, they say that is almost always a bad idea. There is a reason that it will be different, because it will be more difficult to do and you wont achieve an optimal result. Im not saying to do what everyone else does, but most people that do drivetrain swaps know what they are doing, and it would be smart to take their cues.
 
#23 ·
no, see what others have used in their builds for 42-44" tires and go from there.

you're looking at a decent torque motor, though the hp is low for the displacement.
the ax-15 will bolt to it, but you'll strip the input and counter shaft gears in a hurry
the np231 with a wide chain kit and hd sye should live behind a stock 401
the 30spl d60 probably will twist axle shafts when you finally get gearing that is correct for your tire choice, which is at least 5.13 and better would be 5.38
the front 44 isn't acceptable in any way for tires over 37's, maybe 38.5's if you're really light on the go juice and don't get into any mud or rocks. otherwise it'll break shafts like tooth picks.

MOST people building for up to 42's use an hp60 front and a 14b rear, it's cheapest that way. some build custom 14b fronts, some use d70's but those are expensive.
after you get to 44's and up, that's rockwell territory. and that makes it not road legal in pretty much every state of the union.

people who do things just to be different and not follow the crowd on parts also can't follow the crowd on the trail.
 
#24 ·
See my profile. Not exactly what you want to do but close; except for the much larger tire size. Toyo OC M/T's are pretty damn heavy though.

Summary: Brakes/stops fine, handles fine, off roads fine, highway fine with AX-15, cooling motor something to watch for, bolts in with hardly any effort to a prior AMC 6 cylinder (mounts from Advance Adaptors),

Keep it AMC (wink).

PS: I stay away from hammering the 413 cid (401 + 0.060" overbore) when traction is full; large boulders, dry pavement, etc... In any kind of snow, mud....go for it. Dana 30 has hung in there so far (surprised a little), AX-15 getting sloppy (never opened yet after 190,000 miles), TC is fine, ....most of this after ~ 40,000 miles on engine combo.
 
#25 ·
Good to hear. I like the AMC 401 and want to stick with it, I know that it will fit without much effort, was on an engine stand when I bought it so I've seen and heard it run. It will stay pure stock for as long as I have it and won't see high revs or anything of that nature. Should i mention that when I purchased this rig that it had 44" Boggers and a Dana 30 front end and a Dana 35 rear end running 3.55 gears haha and did just fine for a couple years but I don't know the history of the inline 6 before I had it but knew that I would eventually go a different direction with a V8. It all a learning process and appreciate all of the feedback I have been provided.
 
#26 ·
Easy to make decent power from an AMC 401. Mine is 400 ft/#'s or more from ~ 1500 - 4900 rpm. The peak values are 390 HP and 445 ft/#. This purposely cammed for low rpm torque and build for durability. The stock forged cranks & rods are a nice perk, along with the high Ni content blocks for the 401's

Trouble free for many miles now.

Pay attention to the AMC integral oil pump gears / aluminum timing cover setup. Bulltear.com is your friend here. Matt is a great guy, very helpful. I run a remote filter with the steel midplate. Above 40psi hot pressure at idle w/ 5/30 synthetic.
 
#29 ·
By my experience the chevy 10 bolts aren't really that much better than a D35. I've seen them snap in 1/2 tons with 350 cid and TH350 power running 31 inch tires. (I've snapped the one in my suburban, but it doesn't count since it's a beast of a truck anyway).

I've snapped (2) 12 bolts in a 1968 chevy 2wd pickup with just a 325hp 327/th400 running 265/65R15 tires. Just my opinion.
 
#30 ·
Ideally I'd like to have a set of military 1 1/4 ton axles and run my 4.88 gears but we shall see. I've heard both good and bad about the Chevy 10 bolts, just like everything else (ex Ford 6.0 engine etc). There are people out there that like them and have no issues and others have a lemon from the first day. If I snap them then it's not really a big deal because I got the axles and gears for cheaper than I would have been out just buying a set of gears.
 
#33 ·
Very true. It's sometimes cheaper to purchase a few axles of one type than it is to purchase an upgraded version. BUT, who has the time to be replacing axles all the time? I for one no longre can afford to spend my spare time on replacing axles when ihave a little girl who wants me to do things with her, or when I have other things going on.
 
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