4 cyl iron Duke to 6 cyl swap?

City
Terlingua
State
TX
#1
Hey all, I’ve been enjoying driving my ‘81 Scrambler for several months now. My only real complaint with it (at this time) is that I have a significant elevation change in my drive home. About a 2,000’ climb. Going to work I can manage 65 mph all day long...dropping 2,000’. Haha. But the climb home is rough. Maybe 50-55 mph with it floored in places. If I have a headwind I’m really getting the people behind me mad. (70mph posted)

My question is, how hard is it to swap out a 6 cyl for my 4 cyl Iron Duke? Can I keep my transmission?

Thanks
Brad
 

walkerhoundvm

Typical Know-it-all
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#2
It's not too difficult, but I wouldn't be convinced it would help all that much. Maybe a little, but you would probably also want to consider a different transmission and axle regearing. It's the nature of trying to make improvements - you look to do one thing, but it takes upgrading three other things to get there. I won't even go into a V8 conversion, you'd really lose your mind then.
 
City
Halifax
State
UK
#4
Dont think it will bolt straight up as the bell housing mounted on the gearbox will have the Chevy pattern for the Iron Duke and not the AMC pattern so that would need swapping out.
 

ag4ever

Average Nut
LIFETIME
CJ-8.com Member
City
Richmond
State
TX
#5
Easiest swap would be a mild carb'd chevy v8. Mostly due to the bell housing as Dave mentioned.

Keep it reasonable and the stock trans should survive just fine.
 
City
Terlingua
State
TX
#6
It's not too difficult, but I wouldn't be convinced it would help all that much. Maybe a little, but you would probably also want to consider a different transmission and axle regearing. It's the nature of trying to make improvements - you look to do one thing, but it takes upgrading three other things to get there. I won't even go into a V8 conversion, you'd really lose your mind then.
Really, a little is all I’m looking for. If I could maintain 65 mph on the climbs I’d be happy. This is a daily driver, I enjoy the great gas mileage the iron Duke gets, just wish it had a little more HP.

What transmission?
95% sure its the Borg-Warner SR4.
 
City
Terlingua
State
TX
#7
Easiest swap would be a mild carb'd chevy v8. Mostly due to the bell housing as Dave mentioned.

Keep it reasonable and the stock trans should survive just fine.
I had heard the Chevy small blocks bolted up to the bell housing. But also read that they can destroy h transmission as it’s more of a car trans and not a truck trans. I might have to end up going that way but was wondering if I could do it with the straight six. Doesn’t sound like it’s easily possible?
 

walkerhoundvm

Typical Know-it-all
LIFETIME
CJ-8.com Member
City
Cave Creek
State
AZ
#8
I think you're almost as likely to destroy that trans with the I6, especially if you don't reevaluate your gearing. You've got a ton of good info here, and it'll be up to you to price it out, save, and get it done. I would consider an a) engine swap, b) a transmission swap, and c) a regearing. Some of those come with rewiring, some require a new bellhousing, and some will come with having new driveshafts. If you want to stay AMC, an I6 with a T5 and a regear would be a good option. If you're not concerned about stock, then the Chevy engine and a regear would be relatively cost-effective. If you want to go all in, a 5.3L V8, AX15/NV3550, and a regear.
 

ag4ever

Average Nut
LIFETIME
CJ-8.com Member
City
Richmond
State
TX
#10
95% sure its the Borg-Warner SR4.
Given this, I say swap engine and trans.

My ‘82 is a 1JCBN vin. Started life with the 151 iron duke and T5 transmission. The second owner (uncle of the person I bought it from) had it swapped for a ‘79 232 I6 out of and AMC Spirit, and retained the T5. Did that in ‘84 as I recall. He used it in the Sedona mountains for hauling rocks and needed more torque. When I got it the chassis had about 80,000 hard slow miles on it. I ran it from Houston to Llano many times, and it would do 80 down hill in central Texas, and drop to 50 on the up sides. That 232 was really wound up and run hard to get those speeds.

I was going to put a stroker 4.0/258 in it, but decided to go LS. I did not want to have an under powered vehicle. But that is leading me down a path upgrading every part to deal with high horsepower.

That was the main reason for suggesting a ‘90s era Chevy V8 that will have about 250 HP. That with a T5 should live if driven sanely. But since you have the weaker 4 speed, I would skip that and just get a 4.0/AX15 from a TJ or similar. Put a clocking ring on it and bolt the D300 transfer case on it. That will give you fuel injection, more horsepower, and a good overdrive transmission.
 

John N

Addicted....Ex-SOA VP
LIFETIME
CJ-8.com Member
SOA Member
City
Rockville
State
VA
#11
You might consider a Chevy 4.3 V-6. They’re plentiful and cheap, they’ll bolt up to your Bellhousing. Your transmission is still a weak link.
 
City
Terlingua
State
TX
#13
Y'all are giving me a lot to think about. This isn't something that I'll do this summer as I still want to enjoy it as a DD. Probably a winter project but I gotta decide what direct I'll go and prepare.

Interestingly, today I noticed rear TXDOT changed the speed limit on the main road I travel. From 70 to 75 mph. I'm gonna have to figure something out soon so I don't get run over.
 

tower210

Scrambler Junkie
LIFETIME
CJ-8.com Member
City
Olathe
State
KS
#14
Finding 258/T5 packages shouldn't be that hard. I sold one in-tact and running. I've seen several for sale in my area since. Its best if you can see it run/drive it. With all of the LS swaps; it seems this is easy. If you want an auto trans; I'd look for a good 4.0 donor. Those motors and transmissions are a nice combo (and everywhere for like $5). I found a rare low mile AX-15 / 4.0 combo (less than 10% of XJs got the manual) and it turned out great.
 

sdsupilot

CJ-8 Member
CJ-8.com Member
City
OKC
State
OK
#15
I have an 89 TBI 4.3 in mine. Swapped the 258, SR4 and Dana 300 out as I wanted EFI and an auto. It has good power, but hasn't proven to be very economical yet...
 
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