Starting a 6.4 Hemi swap

[JTPatriot]

Let me toss this out there:

Regarding gear ratio... I currently have 5.13

If I was turning the JT into a tow truck, I'd be there

I think I am going to stay in the 37"-39" tire size, so a change to either 4.88 or 4.56 is pending. If I were to have any chance at all of getting any decent fuel mileage, then 4.56 would be the best choice. The Hemi should be able to pull in 8th gear at 80 MPH. But 4.88 would work too and allow me to use high range climbing up things like Engineer Pass

Thoughts?

I have the AMW 5.7 in my Gladiator Rubicon, 2020. I am running 38's, 4.88 gears and I can get 15 MPG's at 80 MPH, just highway cruising. Got that just the other weekend from KS. to TX. and back. Running the stock axles with RCV's in front and chromoly axles in the rear. Brake push thru is an issue even with mine. V8 torque with the Rubicon low transfer case does not help. Need to look at some better brake options.

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[ltdodge]

So...4.56 then???

I’m running a 6.4 with 4.10s and 37” tires. When I did the swap, AMW recommended staying with the 4.10 gearing, and I’m glad I listened.
At 80 mph I average around 13.5 mpg, and in the 65–70 mph range I get about 14.8 mpg. I’m in Florida, so it’s mostly flat terrain, and with this setup the truck stays in 8th gear almost all the time.
I also considered going with the 5.7 when I did the swap, but decided to stick with the 6.4. After driving it, I know I would’ve been disappointed with the 5.7. The 6.4 completely transformed the truck and was definitely the right choice for me.
I’ve had the truck since December 2025 and have already put about 7,000 miles on it as my daily driver.
Would I do it again? Absolutely.

 

[Flyin6]

I’m running a 6.4 with 4.10s and 37” tires. When I did the swap, AMW recommended staying with the 4.10 gearing, and I’m glad I listened.
At 80 mph I average around 13.5 mpg, and in the 65–70 mph range I get about 14.8 mpg. I’m in Florida, so it’s mostly flat terrain, and with this setup the truck stays in 8th gear almost all the time.
I also considered going with the 5.7 when I did the swap, but decided to stick with the 6.4. After driving it, I know I would’ve been disappointed with the 5.7. The 6.4 completely transformed the truck and was definitely the right choice for me.
I’ve had the truck since December 2025 and have already put about 7,000 miles on it as my daily driver.
Would I do it again? Absolutely.

What is the RPM at 80mph?

My Jeep is an AEV JT370. It came stock with 4.56! But I felt it was a sled, so I went with the recommended 5.13. That sort of worked in the same way as putting lipstick on a pig. In the end, you still have a pig.

I placed those 4.56 gears on marketplace where they stayed for almost two years, then sold about six months ago. Perfect Dana/spicer gearsets.

Of course, had I kept the 4.56 gears in the Jeep, well, I wouldn't have kept the Jeep, so it is what it is. The more I think about it, 4.56 seems like the right spot to land. That and stay with a 37"-38" tire. I DO NOT plan to go to much heavier D60 axles. I'm keeping the M220/M210, which are filled with some pretty good parts.

 

[RougeShot12er]

So...4.56 then???

4:56 seems to be what a lot of people run on these.
Really in my opinion, 4:10 would probably prefect for how you use your rig and your current tire size.
Also a lot of people consider 4:10 to be a lot stronger gear set due to the sizes.

 

[Jaxmax]

Staying with 37” and perhaps running the 4:10, would give good MPG , and you have low range for when you need it. Perhaps finding out what they are doing with your brakes and spending a little bit more there is the way to go. Don’t know where I read it but the 6.4 weighs less then the 5.7, but guess that is hearsay now…..Jack
I’m in the 5.7 group , and still hope Jeep throws one in sometime as it would get me to trade my baby!…..Jack

 

[TwoCarGarageYT]

What is the RPM at 80mph?

My Jeep is an AEV JT370. It came stock with 4.56! But I felt it was a sled, so I went with the recommended 5.13. That sort of worked in the same way as putting lipstick on a pig. In the end, you still have a pig.

I placed those 4.56 gears on marketplace where they stayed for almost two years, then sold about six months ago. Perfect Dana/spicer gearsets.

Of course, had I kept the 4.56 gears in the Jeep, well, I wouldn't have kept the Jeep, so it is what it is. The more I think about it, 4.56 seems like the right spot to land. That and stay with a 37"-38" tire. I DO NOT plan to go to much heavier D60 axles. I'm keeping the M220/M210, which are filled with some pretty good parts.

I never saw 40's or 1 tons in my future, but you'll actually have the power to turn them now. I know I didn't get the AEVJT370 with the intention of swapping the suspension, regearing, and bigger tires.....but there I was. I think you've outdone me on the changes to the rig plan, so I don't think you can rules 1 tons out now!

Besides the power to turn heavy axles and tires, you'll have the piece of mind that the added power isn't going to break anything. Ok, anything can break, but it's less likely. If you add up the amount of money you will have into axles after two gear swaps, rcvs, trusses, balljoints, and knuckles your knocking on the door of 1 tons.

I know this because I was there too. The most disappointing part was when I shredded a ring gear in sand hollow. It went quietly on an obstacle, no tire spin, no hard steering angle, nobody even noticed. I heard an intermittent clunking that went away in 2hi which told me what I needed to know. Went to the local shop, opened the front diff cover and out came parts of my gear set. All I had done with all the parts to strengthen the axles was move the weak link to the gear set.

BTW, I went 4.88 gear set for 1 tons and 40s. My 6.4 is really a 7.3 turning 630hp so a little different beast but I'm sitting at ~1900 @ 70mph, 2100-2200 rpm at 75. I rarely go faster than that.

You're this far in...

 

[Flyin6]

I never saw 40's or 1 tons in my future, but you'll actually have the power to turn them now. I know I didn't get the AEVJT370 with the intention of swapping the suspension, regearing, and bigger tires.....but there I was. I think you've outdone me on the changes to the rig plan, so I don't think you can rules 1 tons out now!

Besides the power to turn heavy axles and tires, you'll have the piece of mind that the added power isn't going to break anything. Ok, anything can break, but it's less likely. If you add up the amount of money you will have into axles after two gear swaps, rcvs, trusses, balljoints, and knuckles your knocking on the door of 1 tons.

I know this because I was there too. The most disappointing part was when I shredded a ring gear in sand hollow. It went quietly on an obstacle, no tire spin, no hard steering angle, nobody even noticed. I heard an intermittent clunking that went away in 2hi which told me what I needed to know. Went to the local shop, opened the front diff cover and out came parts of my gear set. All I had done with all the parts to strengthen the axles was move the weak link to the gear set.

BTW, I went 4.88 gear set for 1 tons and 40s. My 6.4 is really a 7.3 turning 630hp so a little different beast but I'm sitting at ~1900 @ 70mph, 2100-2200 rpm at 75. I rarely go faster than that.

You're this far in...

Well, I certainly admire what you did with your AEV, a "lead the fleet" vehicle for sure! Along with owning it came experience, and that is experience I cannot discount.

It will not happen just yet, mostly because of cost, but regarding the subject of axles, I had been considering something. I believe someone makes a D60 rear with the 5ive lug pattern, I think... For the front, I'd prefer a super D-44, 5-lug. Weight is important, and with this setup, I'd be better off. I also am not enamored with purchasing new beadlock wheels and having 8 lugs. Same same with 40's. I just don't see myself really needing them.

In any case, my immediate goal is to get this 6.4 in there and sorted. Maybe put a little trip on it to get some planning numbers. Well before the upgraded axles, which I was not planning for, will come a fix for the limited fuel supply. Adding that Australian Australian aux tank is something that interests me. That and a decent skid plate system.

All this is speculation and dreaming at this point. I save the funds to do these projects first, so there will be some time required, which serves as a natural buffer to give me time to better think it through.

And in the end, we all have seen that I'll make the wrong choice and have to do it all again!! :-0

 

[TwoCarGarageYT]

Well, I certainly admire what you did with your AEV, a "lead the fleet" vehicle for sure! Along with owning it came experience, and that is experience I cannot discount.

It will not happen just yet, mostly because of cost, but regarding the subject of axles, I had been considering something. I believe someone makes a D60 rear with the 5ive lug pattern, I think... For the front, I'd prefer a super D-44, 5-lug. Weight is important, and with this setup, I'd be better off. I also am not enamored with purchasing new beadlock wheels and having 8 lugs. Same same with 40's. I just don't see myself really needing them.

In any case, my immediate goal is to get this 6.4 in there and sorted. Maybe put a little trip on it to get some planning numbers. Well before the upgraded axles, which I was not planning for, will come a fix for the limited fuel supply. Adding that Australian Australian aux tank is something that interests me. That and a decent skid plate system.

All this is speculation and dreaming at this point. I save the funds to do these projects first, so there will be some time required, which serves as a natural buffer to give me time to better think it through.

And in the end, we all have seen that I'll make the wrong choice and have to do it all again!! :-0

LOL, fair enough. Currie makes semi float D60 which retains factory hubs, brakes, and associated parts. Its a more affordable option that provides a bigger gear set. Wouldn't be my first choice. For the expense it's worth going all in at that point and get the additional stopping power and beefy components associated with full float a 1 ton axle.

Weight is a whole different issue. I'm with you. I hit the trails fairly "light" as far as stuff goes. I do haul a camper across country with said "stuff" and it all adds up. I had steel skids that will no longer work with my long arm set up, will be looking aluminum. Also looking at changing my bumpers, again looking aluminum with a few additional criteria. The suspension, axles, wheels, tires are heavy, but at least low. The engine adds weight, but it makes up for it by doubling the power!

 

[ltdodge]

What is the RPM at 80mph?

My Jeep is an AEV JT370. It came stock with 4.56! But I felt it was a sled, so I went with the recommended 5.13. That sort of worked in the same way as putting lipstick on a pig. In the end, you still have a pig.

I placed those 4.56 gears on marketplace where they stayed for almost two years, then sold about six months ago. Perfect Dana/spicer gearsets.

Of course, had I kept the 4.56 gears in the Jeep, well, I wouldn't have kept the Jeep, so it is what it is. The more I think about it, 4.56 seems like the right spot to land. That and stay with a 37"-38" tire. I DO NOT plan to go to much heavier D60 axles. I'm keeping the M220/M210, which are filled with some pretty good parts.

 

[Flyin6]

That's low (Nice)
Should fetch decent fuel economy

 

[RidinDirty]

I have the AMW 5.7 in my Gladiator Rubicon, 2020. I am running 38's, 4.88 gears and I can get 15 MPG's at 80 MPH, just highway cruising. Got that just the other weekend from KS. to TX. and back. Running the stock axles with RCV's in front and chromoly axles in the rear. Brake push thru is an issue even with mine. V8 torque with the Rubicon low transfer case does not help. Need to look at some better brake options.

Probably coming up on a brake change for me... What do you think of the Teraflex option?

 

[JTPatriot]

Probably coming up on a brake change for me... What do you think of the Teraflex option?

I keep looking at them, just can not pull the trigger as for daily driving I really do not have an issue, although everyone that drives it says it takes a lot of brake push to get stopped, probably me just used to it, lol. They seem to be the best bolt on and they use, I believe Tundra brake pads, easy to get.

 

[Tim]

Probably coming up on a brake change for me... What do you think of the Teraflex option?

I installed Teraflex brakes last weekend. I highly recommend them. Prior to the Teraflex kit I had Powerstop rotors and pads on the front and there is no comparison. The Teraflex kit is a worthy upgrade.

 

[Flyin6]

I installed Teraflex brakes last weekend. I highly recommend them. Prior to the Teraflex kit I had Powerstop rotors and pads on the front and there is no comparison. The Teraflex kit is a worthy upgrade.

I am currently using powerstop pads and rotors on all four corners.

 

[Tim]

I am currently using powerstop pads and rotors on all four corners.

Even though I only had them up front, the Powerstop pads and rotors were a noticeable upgrade from stock. I was quite pleased with them. My Gladiator just turned over 100k and my rear brakes were still stock and pretty much done. So my assessment may not be 100% fair, as I am comparing front Powerstops with 40k~ish miles on them and clapped out rears to brand new Teraflex Delta brakes all around. The Delta brakes definitely give a nice firm pedal and gobs of stopping power.

I am super interested in your v8 swap. I plan to keep this truck a long time, longer than my Pentastar will likely last...

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