Hey guys and gals,

I looked through this forum and a few other but I couldn't find am answer. I am going to do a 6.4L Hemi and an 8 speed 8HP70 swap into my 2010 JKU sport in the spring. I will also be swapping axles at the same time. But I don't know what gearing to get. I'm currently running 33's but plan to run 37s

 

With that kind of power and transmission, I’d go with 5.13’s. If you gear it too low you’re more likely to break stuff.

Be sure post pics and share details with us on the progress.

 

i have the 6.4 with 545rfe and run 5.13 on 40s and previously on 37s. works perfectly for my use.

 

Will do. thanks for the info.

 

Ben is opening up everyone's wallet these days.

 

Gear Ratio Calculator



if you want real data to base ur choice on this may help

 

With that kind of giddy up I would stay around 4.88s with 37's otherwise you will be able to pass everything except a gas station. I run 4.10's on 33's and absolutely wonderful offroad manners with the V8 which is way less in size and slightly higher gas mileage than the V6. Also the V6's tend to slip the converter a lot on obstacles offroad and have to rev up whereas the V8 just chugs over with the same gearing. Yeah 40's would need a higher ratio like 5.13. Don't forget you pick up a really low first gear in the 8 speed autos plus some TC slip. My Chev 8 speed is 4.56 in 1st.

 

I ran a 6.4 Hemi with 4:10 gears here in the altitude and it was fine with 35" tires. Had I gone to 37" tires a 4:56 would have provided me with more acceleration. The beauty of the big engine is you can run a more friendly gear ratio. When you drop down in mid 4's - 5 series gears the pinion size really shrinks.

 

I'm running 6.4 with 4.10s on 37s. It's been a great balance on and off-road.
When I swap to one tons, I'm going to 4.56 or perhaps 4.88 to account for the added axle weight and possibly 40s+.
I personally believe 5:13 will be too low.
Would recommend calling a few of the shops that make conversion kits to get their feedback (Dakota, AMW, etc) as they will have the most real world experience.