AMC401 or LS

Jeeper_4_Life

Scrambler Rookie
LIFETIME
CJ-8.com Member
SOA Member
City
Kingman
State
Ks
#1
This will probably be longer than I want it to be, but figure the back story is relevant. My Scrambler has gone from 151 Iron Duke, to a Buick 231, to an AMC304 over its life. The Buick to AMC304 I did because the SR4 transmission wouldn't stay in reverse and I was tired of it. I wanted to go to an NP435. When I went to swap it out the transmission tower was going to force me to cut my tub or move the motor back. I didn't want to deal with re-positioning the motor when I wanted a V8 anyway and I refused to cut my tub. My dad had the AMC304 rebuilt from a wrecked jeep back in the early to mid 90's. It sat on an engine stand wrapped in plastic and covered with a blanket until 2014 or so when I resurrected it. It had never been ran until I put it in the Jeep. I broke the cam in the way they say with comp break in oil, and drove it highway as much as I could to vary the RPM. It seemed to run okay and didn't have any really problems for the 1st year, other than it would drink oil if you ran it down the highway, but wouldn't smoke.

3 years ago I added FITech efi to it when I changed axles and suspension out. We went to Colorado after I got it done. After sustained RPM's up a mountain pass it developed an oil leak. I have fought that since that point up to a few months ago. Can drive around town and crawl for days and dry, but run it at highway speeds or sustained RPM for more than 40 min, oil everywhere. I resealed my intake, front cover, did some DUI distributor mods and got it to stop leaking after driving 50 miles at sustained rpm. Thought maybe I had won. We went back to Colorado this past month and on the way home I lost a trailer wheel bearing, and was forced to drive the jeep the remaining 430 miles, as I didn't think i could get the trailer fixed. Each gas stop, which was often, I looked for the oil leak to show up, which stayed dry all week on our trip. I made it about 380 miles before it started dripping. It is still much better than before, other than it took a quart of oil to travel home. It doesn't smoke that I can tell and has okay power as long as your not at altitude. I need to do a compression check, but I am to the point I believe the rings didn't seal or are stuck, the cylinders are glazed making crank pressure (PCV has been checked repeatedly), or I still have an intake issue. If either of cylinder thoughts are true then I have to tear it down. If it has to come out I don't want to put it back in.

I have an AMC401 on a stand that I could tear down and go through to see what it takes to rebuild, or I could find an LS.

I have been following this thread, but didn't want to hijack it as it had good info for what he was looking for. Posts 23,24,25 provided me some good info.
https://www.cj-8.com/threads/amc-360-build.48836/page-2#post-404027

I also read through this older thread and it had mixed opinions and seemed like the 401 was the choice to do.
https://www.cj-8.com/threads/opinions-on-engine.37289/

I know the 401 is going to cost $ to rebuild even if I don't have to do machine work and can get away with just pistons, bearings, cam, new timing cover, oil pump etc. Locally around KS am I not sure where I would take it to have work done. The Jerry Tucker post from the thread above was informative, but a long ways from KS. With the 401 I have to change nothing with my current setup, just put the motor together and it goes in the jeep. I already have EFI that works okay, hoping it will work better if the motor doesn't have possible internal issues. The LS I have to find, have harness work done, redo motor mounts, bellhousing to NP435, redo clutch setup, exhaust, probably have to do electric fans as well. Although the motor part of an LS swap using a 5.3 or 6.0 with a cam swap would be cheaper, the external items add up. I have not priced everything, but I can guess it would offset the cost vs the 401. The LS would maybe get better fuel mileage (better than 10 I get now?), would be more reliable, leak less oil in time, probably last longer, and probably make enough power to make me happy. As I understand from research the 401 should make more torque across the rpm band vs the LS until the upper RPM's which would be nice on a trail or just off idle. The 401 would also make enough power to make me happy and the exhaust note too.

I do a little of everything highway, around town, Colorado trails, semi local rock parks, and sand dunes. It would be nice to be able to drive the heep across country, but will probably continue to haul it. I am kind of stuck on what to do. The more I read and research the more I think going with the 401 is the best route. If I didn't have it the choice would be easier.

Anyone have thoughts on which route to go?
Anyone gone from a 360 or 401 to LS or vice versa? What did you like or not would you do it again?
Anyone have recommendations on AMC engine builder near KS?
Anyone have a ball park estimate on cost to rebuild AMC V8 from a decent builder, such as Jerry Tucker? I can add up the costs for all the parts, but machine work, head work I do not have a grasp on cost.
 

wjtstudios

1985 CJ 8
LIFETIME
CJ-8.com Member
SOA Member
City
Rochester
State
Mi
#2
I haven't driven either so I can't help you much there.

My conversations with Jerry over the last week and a half have lead me to a moderately built 360, which he is supplying the block, for around $4,800-5,400. But we are still getting the specs put together for the build. But that was the range we discussed in our last conversation. He is willing to ship it up to Rochester, Michigan for me, so the distance is not as much of a factor. I am not sure what the shipping cost will be. The biggest factor is selecting Jerry is his Passion for the AMC engines. He experience with them, in my opinion, is worth the investment verses having a local shop handle the work. I may save a little in the beginning if I went somewhere else, but in the end, would end up spending more with repairs and upkeep. This will give me a good foundation for years to come.
 

mwqpd11

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Coopersburg
State
PA
#3
I had a 401 built 2 years ago. It cost me around 5k. I keep AMC in all my jeeps. You already have the EFI so I say keep the 401
 

sdsupilot

CJ-8 Member
CJ-8.com Member
City
OKC
State
OK
#4
I don't think you will be disappointed with either option. Put a spreadsheet together to estimate time and expenses for each option. Factor in how much of the work you are comfortable to do yourself.

I would go LS. Parts are available everywhere, troubleshooting is pretty easy and its an extremely common swap.
 

sxer

Legacy Registered User
City
Little Falls
State
Mn
#5
I had the exact same problem as you. I had rebuilt my 258 and it sat on the stand for more than a year while I waited to finish the rest of the Jeep. When I had it all finished and started to drive it, it used oil at the rate of about 600 miles per quart. I didn't see any smoke either. I too assumed I had scuffed the cylinders or something from cranking the engine when it was dry. I did prime the oiling system before starting for the first time. I tried all different weights of oil with no change. Finally, not knowing if I had the correct PCV, I removed it and replaced it with a breather. At the same time, since I only drive it in the summer, I went with straight SAE 30 oil. It immediately went to being down about 1/2 quart at 3000 miles and an oil change. I'm not sure what happened, if it did indeed have the wrong PCV, the rings magically sealed, or the 30 wt had something to do with it. It has remained the same through several oil changes. I'm afraid to install a PCV or switch oil weights in fear it will go back to it's old habits. I suppose I will to try to figure out what exactly was the cure.
 

Ron84cj

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Bend
State
WI
#6
As far as gas mileage goes. The worst I have gotten with my 5.3 with a 5 speed was 16. I have hit 20 mpg cruising at 60. On the other hand, the 401 would be awesome. But if you have to go through the heads which you most likely do, I would give serious consideration toward the aftermarket aluminum heads. You would be very surprised that many times the cost between the new ones and the price of rebuilding junk heads from the 70s may not be that far apart. Then you will get more power and most likely better fuel economy because of the way more efficient heads. Cylinder heads from the 70s really really suck. Just me 2 cents
 

Jeeper_4_Life

Scrambler Rookie
LIFETIME
CJ-8.com Member
SOA Member
City
Kingman
State
Ks
#7
As far as gas mileage goes. The worst I have gotten with my 5.3 with a 5 speed was 16. I have hit 20 mpg cruising at 60. On the other hand, the 401 would be awesome. But if you have to go through the heads which you most likely do, I would give serious consideration toward the aftermarket aluminum heads. You would be very surprised that many times the cost between the new ones and the price of rebuilding junk heads from the 70s may not be that far apart. Then you will get more power and most likely better fuel economy because of the way more efficient heads. Cylinder heads from the 70s really really suck. Just me 2 cents
Summit wants $1085 per head for Edelbrock's. :oops: From what i have read on the interwebs AMC heads flow really well? I haven't had time yet to call people on what it costs to have them redone, but surely it can't cost $2170 for the pair even having them machined for studs to run rollers?
 

Ron84cj

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
West Bend
State
WI
#8
Just flow numbers aren't everything. The combustion chamber on those old cylinder heads do nothing for efficiency. Very often it is not hard to have $1000 into rebuilding old heads. Especially if you have earlier heads that don't have hardened valve seats. I didn't realize they were quite that expensive. But honestly, I personally would spend the extra money. Nowadays engines make way more power and get way better fuel economy. That is NOT only because of EFI. Yes EFI makes a big difference, but a lot has to do with the engine itself. Port flow, combustion chamber shape, the way intake manifolds flow, is what makes the difference. My firebird is a prime example of this. My 400 hp 334 ci sbc very regularly got 23-24 mpg on the freeway going 80 mph....And it was carbureted.
 

mwqpd11

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Coopersburg
State
PA
#9
The 401 is great but the fuel mileage is horrible in mine. If your going to drive a lot you may want the LS.
 

AdamH

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Mt Holly
State
NC
#10
As you know from the thread above I am a 5 time customer of Jerry's and personally will always stay AMC with any CJ I build. Given what you already have at your disposal of course I'd say 401.

However, if staying AMC doesn't mater I'd be lying if I said going AMC was the all around best option (power, aftermarket support, etc). There's a reason so many go bowtie in their CJs - mainly for bang for your $$.
 

barrys

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
East Norriton
State
PA
#11
A complete running or rebuildable 401 shiuld bring in over $1000. Something to consider when thinking about choices. Your current drivetrain parts would add more money to fund an LS swap also.

I have a 401 in my CJ8 but have put very few miles on it since buying it years ago. Having a 401/6.6 liter engine in a CJ sound cool when you tell people also.:headbang:
 

Boomer

Iron Bender
City
Snohomish
State
WA
#12
Been going through this debate/mental exercise myself. I have accumulated 2 complete 401 engines, accessories, a York compressor, MORE bombproof mounts, Edelbrock intake, Holley TA 670 carb, DUI HEI ignition, 4 core aluminum radiator, NV4500 adapted to run between an AMC or SBC and a Dana 300, AA AMC/NV4500 bellhousing and probably a few other things that I am not remembering.

I like the idea of “Keeping it Jeep”, but I am having a hard time stomaching the idea of spending thousands to rebuild a 401 only to be left with a cranky old cabureted gas guzzling engine when I could buy a LM7, LQ9, etcfor a fraction of the price, sell off the AMC specific stuff and use that money adapting the LS engine into the CJ. This is something that I want to be able to drive for hundreds of miles on the highway.

Decisions, decisions....
 

Boomer

Iron Bender
City
Snohomish
State
WA
#13
LOL, just saw this while perusing Craigslist to check on local AMC prices. Maybe it’s a sign.

809709BA-B81E-481A-BFAD-956EDB1440A1.png 31226EC0-8E1A-4ECD-9630-E39CB090DD97.png
 

Jeeper_4_Life

Scrambler Rookie
LIFETIME
CJ-8.com Member
SOA Member
City
Kingman
State
Ks
#14
A sign to buy it or go LS. Kind of wonder why they would be selling a just rebuilt 401 to put an LS in....
 

Boomer

Iron Bender
City
Snohomish
State
WA
#15
I was taking it as a sign to go LS., but maybe I am already predisposed in that direction. Assuming (Yes, I know how that breaks down) that that the 401 received a decent rebuild and he still isn’t satisfied with the performance, fuel economy, drivability, etc. Maybe I will respond to him to pick his brain a little and see if he is willing to share his thoughts. Heck, he lives in the next town over from me.
 

walkerhoundvm

Typical Know-it-all
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#16
I like the idea of “Keeping it Jeep”, but I am having a hard time stomaching the idea of spending thousands to rebuild a 401 only to be left with a cranky old cabureted gas guzzling engine when I could buy a LM7, LQ9, etcfor a fraction of the price, sell off the AMC specific stuff and use that money adapting the LS engine into the CJ. This is something that I want to be able to drive for hundreds of miles on the highway.
I'm going through an LS swap right now. Seems like you have a lot of the nickels and dimes, so that's good. Every day it seems there's something that pops up I need to include. Adapters, harness reworking supplies, exhaust manifolds, I'm basically hemorrhaging cash at this point. Save a little here and there, find ways to spend it somewhere else. I think it'll be worth it in the long run, but damn if I'm not using eBay and Amazon on a daily basis lately.
 

93_Fummins

CJ-8 Member
CJ-8.com Member
City
Edmond
State
OK
#17
Standalone EFI stuff is coming along pretty nicely, and more affordably every day. Just food for thought adding an edge to the old carb'd mills.

Just running quick numbers of refreshing the 351w in my YJ, adding EFI and transplanting it to my CJ-8 runs pretty close price wise with sourcing a good LS with all the needed accessories and computers. LS swaps really aren't as cheap as they sound when you start adding up all the nickel and dime stuff.....but it's the adaptability, tuning ability, and part availability that make them much more lucrative.
 

Boomer

Iron Bender
City
Snohomish
State
WA
#18
What kind of nickel and dime stuff with the LS are you guys running into?

For an LS/NV4500/Dana 300 drivetrain I am thinking:
  • LM7 complete with all accessories including ECM, gas pedal, etc
  • Modifiy the OEM harness
  • Radiator/hoses
  • Power steering hoses
  • Exhaust
  • Motor mounts
  • Bellhousing/flywheel/clutch
  • Transmission/transfer case crossmember
  • Modified/custom drive shafts
  • Electric fuel pump
I am sure that I missing some small details and would run into the inevitable snags that always arise during projects like this. Curious as to what insights you have to offer.

I would have to most of that stuff installing a 401/NV4500/Dana 300 combo, too. I would undoubtedly run into some nickel and dime going that route, too.
 

Boomer

Iron Bender
City
Snohomish
State
WA
#19
I'm going through an LS swap right now. Seems like you have a lot of the nickels and dimes, so that's good. Every day it seems there's something that pops up I need to include. Adapters, harness reworking supplies, exhaust manifolds, I'm basically hemorrhaging cash at this point. Save a little here and there, find ways to spend it somewhere else. I think it'll be worth it in the long run, but damn if I'm not using eBay and Amazon on a daily basis lately.
By the way, do you offer those custom dash lights? Might want a CHECK ENGINE if I go the way of the LS.
 

walkerhoundvm

Typical Know-it-all
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#20
By the way, do you offer those custom dash lights? Might want a CHECK ENGINE if I go the way of the LS.
I did, but I've gotten out of that a few years ago. I may still have the documents on my hard drive at home, but it would take some effort to get images produced again.

I saved exactly one for my build, of course :)

  • LM7 complete with all accessories including ECM, gas pedal, etc - in the neighborhood of $2k for me, engine ~100K miles
  • Modifiy the OEM harness - about $200 for tape, loom, wiring, relay and fuse parts, blah blah blah
  • Radiator/hoses - $400ish
  • Power steering hoses - not sure on this one yet.
  • Exhaust - not sure yet
  • Motor mounts - $150 or so
  • Bellhousing/flywheel/clutch - through AA this ran me about $1400, but I mainly wanted to avoid the headaches of searching for random old parts and discovering whether they worked or not
  • Transmission/transfer case crossmember - hopefully this can be avoided, but the original will take some mods
  • Modified/custom drive shafts - Tom Woods, ~$400. My builder wanted to go with some local guy running about $400 PER!
  • Electric fuel pump + fittings, etc - $150
  • VSS - $40
  • Exhaust manifolds to fit the engine bay - $200 from a C6 corvette (none of this is getting any cheaper)
  • Computer programing - $75-125
I'll probably have a damage report in my build thread when the dust settles, but honestly I don't want to add any of this stuff up right now.
 
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