Jeep Wrangler Forum banner
  • Hey everyone! Enter your ride HERE to be a part of September's Ride of the Month Challenge!
1 - 19 of 19 Posts

·
Registered
Joined
·
231 Posts
Discussion Starter · #1 ·
I have a 91 wrangler with a 2.5l 4cyl in it right now and I'm thinking of doing a 4.0l 6cyl swap. But am wondering what all I will have to exchange to have a inline 6 in it. New tranny new axles to transfer ext. I currently have Dana 30 in front and Dana 35 in rear. Any advice is helpful thanks.
 

·
Premium Member
Joined
·
62,805 Posts
You don't need new axles or tranfer case, depending on what trans you have, you may not need one of those either

You basically need new motor mounts, engine computer
 

·
Registered
Joined
·
2,585 Posts
Typically you are going to need to swap everything out, because the stock 2.5L 4.10 gearing is just too short for a 6 cylinder, they aren't made to run at high RPM's like the 2.5L is.
 

·
Registered
Joined
·
15 Posts
If you are planning to upgrade, my recommendation is to go to something with a little more HP than the 4.0. I recommend something along the lines of a 4.3 which is simple to repair and has more HP and torque than that of the 4.0. The 4.3 is also a 350 sbc so parts are simple to come by. You will need to replace the tranny and possibly the transfer if it does not match up with the output shaft. Gearing wise, I am unsure for the 4.3 but if you go 4.0 then the stock gears are just fine unless you start increasing lift and tire size.

Hope this helps and please keep us posted as you go (since I will be upgrading my engine as well here shortly).
 

·
Registered
Joined
·
2,585 Posts
OP, disregard the above message. There's more 4.0's out there running on 4.10's and lower than you would ever imagine. That being said, you will need to swap out the tranny and transfer case.
You would know, you have experience with 2.5L's. You're quite full of heresy, fwiw.

Without going to a bigger tire size, (32-33") then 4.10's is TOO SHORT of a gearing, you're going to be running your 4.0 at ~3000rpm's at 65mph on the highway. It's not made for that, it's made to run below 2000rpm at 65, that being said people roll the stock 3.07 gearing with 31" tires just fine in 4th at around 2400rpm. It's still a bit high for that engine, but it works alright.

Then you run into the issue with the D35 itself. Which is not built for tires that big. 31" tires is pushing it, some people have more balls than brains and push it to 33"+. If that axle has known to bust open with stock tires on the open road without the driver pushing it, then evidently it's not a good axle. The only reason I have a D35 back under me is because A. It was given to me for free, and B. It's holding me over until I can go with something stronger. Quit being such a fool.
 

·
Commercial MemberX
Joined
·
8,641 Posts
When you own a 4.0, then you will be more qualified to respond. Your 100 percent wrong fwiw. We have run 4.56's on 33's with a 3 speed auto for 13 years in 5 different YJ's without issue. Read what you want but experience will always prevail.....sorry :(
 

·
Registered
Joined
·
231 Posts
Discussion Starter · #8 ·
so new motor mounts and computer. my friend has a 4.0l and has same tranny and transfer as me. idk about his axles though. i just need to know what all i need to exchange. im getting a 40l that is around same year as my yj that way i dont have to do to much welding. im already running 32in tires on it but thats how i bought jeep. idk what gears im running. more than likely stock.
 

·
Registered
Joined
·
495 Posts
I've got a 2.5 with which i have done the 4.0 throttle body, 5.0 Mustang Injectors, Custom Air intake

all of which have only increase my throttle response and gave me 5th gear back, but still not enough to gain power or speed (all of this did only cost me $50 or so)
 

·
Registered
Joined
·
4,965 Posts
Like already stated it isn't a easy job to upgrade to a 4.0. Similar fabrication work to install a v8. Its a shame it doesn't drop in place of the 2.5.

There are things that can be done to improve performance but most of the time the juice ain't worth the squeeze.

Gearing is very important part of jeeps. With a 2.5l and 32" tires a higher gear such as 4.56 or 4.88 would be the most noticeable in regards to power.

As far as the rpm comments the 4.0 is a great reliable engine but when you weigh one down with gear/armor and larger tires you need the rpm to keep it going. My TJ has 35" tires and 4.88's. Just returns everything close to stock from a gearing stand point.

To be fair you are in tough situation. Engine swap will be a lot of time and fab work.
 

·
Registered
Joined
·
2,585 Posts
When you own a 4.0, then you will be more qualified to respond. Your 100 percent wrong fwiw. We have run 4.56's on 33's with a 3 speed auto for 13 years in 5 different YJ's without issue. Read what you want but experience will always prevail.....sorry :(
I was speaking about a MANual transmission, not a automagic :whistling:

I've got plenty of experience with a 4.0. (this is the part where your buddies always call you to come over and help out because they're too lazy to do the work themselves)
 

·
Administrator
Joined
·
12,630 Posts
You would know, you have experience with 2.5L's. You're quite full of heresy, fwiw.

Without going to a bigger tire size, (32-33") then 4.10's is TOO SHORT of a gearing, you're going to be running your 4.0 at ~3000rpm's at 65mph on the highway. It's not made for that, it's made to run below 2000rpm at 65, that being said people roll the stock 3.07 gearing with 31" tires just fine in 4th at around 2400rpm. It's still a bit high for that engine, but it works alright.

Then you run into the issue with the D35 itself. Which is not built for tires that big. 31" tires is pushing it, some people have more balls than brains and push it to 33"+. If that axle has known to bust open with stock tires on the open road without the driver pushing it, then evidently it's not a good axle. The only reason I have a D35 back under me is because A. It was given to me for free, and B. It's holding me over until I can go with something stronger. Quit being such a fool.
1. Play nice

2. Based only having 4.0L 4.2L or V8s in ALL my jeeps(you can see all the model years below) Having a 4.0L with 4.11's(stock axles form a 2.5l) on close to stock tires.(which has anyone asked what size tires the member is using?) is not an issue. Keep in mind the later TJ's came with 3.73's and 30" or 4.11's(rubicons) and 31's from the factory with the ax15's and rubi's later NV 3550's which are geared lower.
 
1 - 19 of 19 Posts
Top