AMC 20 how much HP can it take?

[Chipw]

I'm probably going to replace my iron duke with a chevy small block v8. I know I'll need a new tranny....and probably a rear end as well...

When I bought the jeep the AMC20 had trusses welded on, one piece axles, a Detroit locker with 4.88 gearing. In other words, I got a nice rear end that I'd really like to keep if possible. I need a new motor and rather than try and rebuild the iron duke, I figure I'll drop a v8 in.
With the mods I have in my AMC20 , do you think I could get by without changing it?

I don't have an engine yet but the mechanic has experience swapping a chevy motor into Jeep's but nothing else. So he's leaning Mr to go that route

Thoughts?


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[tarry99]

Without seeing the truss , I assume they also welded the axle tubes to the center cast Iron housing in multiple spots?

I think your fine for the V8............big tires could change that.

 

[Lumpy Grits]

Run it till when it breaks.
I am no fan-boy of that 20 rear. This from someone who has set-up many of'em
If you plan to build up this SBC. I would start look'n at a 60 or HD Ford 9".
What tranny and t'case are you going with?
You may do well to upgrade the front 30 also.
LG

 

[Peanut Butter]

My first question and it should be yours, is what am I going to do with my Jeep. What kind of driving will I be doing - daily driver, mudding, rock crawling, trail riding, etc. From there your choices with what you change or how you build you Jeep will all depend on how you answered that question. Next big question is how much money do you want to spend?

A lot of people buy a project vehicle with the idea of what they want to do with it. What happens about 75% of the time is they start and before long they are way in over their heads. Not mechanically, but time and money.

Rebuilding you iron duke will be a lot less money than a SMB Chevy and Transmission . Your current setup is awesome in many ways. Somebody went to a lot of trouble to change the gears in the front and rear. The also did all the necessary mods to the rear axle to handle 33's and low gearing. I believe you also mentioned that you were going to have a mechanic shop do the work. There will be new motor mounts, new Transmission mounts, an adapter to connect the Transmission to the Transfer Case , exhaust changes, not to mention the cost of the SBC and Transmission . Adapters go for around $400 to $500. Without the adapter, throw in the cost of a Transfer Case then. As you can see the dollars start to add up.

I'm not trying to discourage you, I just want you to be realistic with yourself. Be sure to get a complete quote for all the work before starting from your mechanic. What ever you decide, it's you Jeep so have some fun with it, just don't end up with a project that sits for years and you never have any fun with it.

 

[Hedgehog]

I had an iron duke in my '80 CJ5 . For it's size it was a good little engine.

With that being said, You are running 4.88 gears. That will take some stress off the AMC20 along with the truss and solid axles. You are about as good as it gets for a 20. I agree with Lumpy, run it until you break it. You just might NEVER break it.

Pay attention to what the others are saying. Have an idea about what the intended purpose is for your Jeep. Example: There is no sense in setting your trails up jeep for drag racing.

 

[Chipw]

Thanks guys. As always the detailed replies give me lots to think about and great advice.

I bought this jeep for 3 reasons.
1. moderate four wheeling. I won't be rock crawling but do want good four wheel capability
2. (Almost ) daily driving. I have a reliable pick up but been driving the jeep 3-4 days a week
3. The big reason was to learn to work on cars.

I've done a few things like change all the fluids and put a new differential cover on the rear. But My mechanical skills are Limited though. I've found a shop where the mechanic will let me help as long as I pay him full price. He told me he'd rebuild the old engine or put in a V8 and I could help with both. Either way , I'm going to learn a lot.

My thinking with the V8 is that it will make a better daily driver, especially with an auto tranny(not sure on that one yet).

I've got up to 20k to drop into this, a flexible time schedule but very little mechanical knowledge.




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[Knighttime85]

I have a 383 SBC with a mild cam in mine with one piece axles, a spool, stock gears, and 33 inch tires. Ive not had any problems with my AMC20 and I wheel it pretty hard.

 

[Peanut Butter]

Thanks guys. As always the detailed replies give me lots to think about and great advice.

I bought this jeep for 3 reasons.
1. moderate four wheeling. I won't be rock crawling but do want good four wheel capability
2. (Almost ) daily driving. I have a reliable pick up but been driving the jeep 3-4 days a week
3. The big reason was to learn to work on cars.

I've done a few things like change all the fluids and put a new differential cover on the rear. But My mechanical skills are Limited though. I've found a shop where the mechanic will let me help as long as I pay him full price. He told me he'd rebuild the old engine or put in a V8 and I could help with both. Either way , I'm going to learn a lot.

My thinking with the V8 is that it will make a better daily driver, especially with an auto tranny(not sure on that one yet).

I've got up to 20k to drop into this, a flexible time schedule but very little mechanical knowledge.

So now we have a little more to work with. I personally would rebuild the V6 as it keeps the Jeep all Jeep. You however my want to go the V8 route. Either way you have a great opportunity to learn a lot about your Jeep.

Some other ideas to consider: AMC V8, AMC I6 AMC 258 i6 / 4.2l or the 4.0L with fuel injection. This way you can keep the it all Jeep.

For the SBC that is pretty straight forward for the engine, Transmission is the biggie. The GM Turbo 400 is a natural for this with adapters readily available. Go here to look: https://www.novak-adapt.com/ Lots of good information in the tech section. There are some other good GM transmissions, but the electronics they need makes those choices one you must carefully consider. Transfer Case - Dana 300 is very popular and easy to hook up to the GM Turbo 400 . The ultimate Transfer Case is the Atlas. (Atlas Transfer Cases | Chevy Transfer Cases | Advance Adapters)

Take some time to read everything you can. When you get to the point that your pretty sure what engine you want, Transmission , post again for some more suggestions. 20K can be spent really quick with lots of changes. Make sure you've made the best decisions for what you'll use.

 

[Lumpy Grits]

Let me add-Are there any Jeep clubs in your A/O you can contact for 'hands-on' info?
LG

 

[Chipw]

Let me add-Are there any Jeep clubs in your A/O you can contact for 'hands-on' info?

LG

Searching for ones now


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[Chipw]

So now we have a little more to work with. I personally would rebuild the V6 as it keeps the Jeep all Jeep.

.

Its a 4cyl. but your comment "keep a jeep a jeep" is exactly what the mechanic said to me. So were rebuilding the original. Its going to be a lot of fun, I cant wait.

 

[Hedgehog]

When rebuilding the Iron Duke be aware that there are or at least were several performance upgrades available. It was in the Fearo (sp) and a few others that were considered to be mild sports cars at the time.

 

[007]

When rebuilding the Iron Duke be aware that there are or at least were several performance upgrades available. It was in the Fearo (sp) and a few others that were considered to be mild sports cars at the time.

Agreed. I think you've made a wise choice here and a fresh Duke will serve you well. As to performance upgrades, they're out there, and if you can swing it now, there's no better time to do them.

 

[BajaEdition]

jeep built its reputation of being the baddest 4x4 anywhere using 4 bangers, remember HP breaks things.
I know a lot of jeeps running AMC 20s with no issues and some do a lot of extreme rock crawling, but none of those has made the mistake of putting a V8 in front of that rear end

like to watch 4x4 videos, ever notice that those squids all make their rear ends go Snap real loud revving v8s because they have no clue how to wheel.

I have been wheeling for close to 40 years and I can say that slow gets you places, fast breaks things, my 3 favorite 4 wheeling engines have been the Dauntless Buick 225 V6 , the toyota 22r and the 2.6 liter in my 2004 wrangler, each of those were very great wheeling engines, after those the jeep strait six and the iron duke rate real high. The only time I have felt the need for a V8 is when wheeling a full size Chevy.

Stick with the Duke, and you will get a better experience.

 

[Hedgehog]

Even though my CJ has a V8 and I don't consider myself to be a "squid" I completely agree with what you wrote. As my dad used to say, "Willys jeeps didn't have enough power to get stuck." I agree with him on that. My '80 CJ5 had a GM 151 Iron duke in it and an AMC20 , it went everywhere I wanted to go and did alright on the highway. When the SR4 couldn't be properly rebuilt, it was upgraded to a Buick 231 and Ford T-18 . Nothing kept that thing back with more power than we needed.

 

[Lumpy Grits]

If-you want to play hard. You, pay hard.
I like HP, yet I still run a pretty much stock AMC 258 i6 / 4.2l .
IF, I didn't have to play the SMOG games here. There would be a built 401 in my '7'.


LG

 

[Posi]

Those great 4cyls in the day came with 5.38's from the factory
The duke, 4.10
Gearing is the difference maker.
I have a friend running a tj 4cyl with 42" tires and he beats the snot out of it and he hasn't kill it yet (going on 5-6 years). He also has 5.13 in the diff and a Atlas.

 

[007]

One other thing to consider is that many of us with a V-8's are running relatively stock V-8's and as such have only marginal horsepower and torque increase over the I6. I'm not where I can look at the exact numbers, but it is indeed marginal at best. So in situations like those, just like mine, there's no concern over whether or not the 20 will handle the power of a V-8 like mine. And like Posi said, gearing is what makes all the difference in the world. I love horsepower as much as the next guy, but I've never had a need for more than what I have.


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[Lumpy Grits]

The biggest issues I have seen in my years or re-gearing the '20' is the thin axle tubs and number of times I've seen the 'pumpkin' rotated on the axle tubes.
Both of these issues happened to my 20 and why I decided to upgrade and not 'band-aide'.
LG

 

[hagar]

It will take a lot. This Jeep still has factory axles and rear hubs.