Re-gearing math?

Yeah this motor I’m using isn’t a 400+HP beast so cannot get away with using just a single gear. I AM using 1st, 2nd, and 3rd up to 60mph. I don’t go above that, no highway driving for me, until I have this 100% sorted out.

I love rowing through my own gears and I do plan on taking it for some light off-roading so want to preserve transfer case.

There are some that are running this motor with a single gear but that’s on sub 2,500lb, older classics and sports cars whose original HP was in the 60-100hp range.
 
Yeah this motor I’m using isn’t a 400+HP beast so cannot get away with using just a single gear. I AM using 1st, 2nd, and 3rd up to 60mph. I don’t go above that, no highway driving for me, until I have this 100% sorted out.

I love rowing through my own gears and I do plan on taking it for some light off-roading so want to preserve transfer case.

There are some that are running this motor with a single gear but that’s on sub 2,500lb, older classics and sports cars whose original HP was in the 60-100hp range.

You are right. You would need an axle ratio of around 2.0 to be able to run a single gear, obviously, your low-speed power would suffer greatly. You were asking earlier what the best gear ratio is to pick. IMO I would go with the highest (numerically) gear possible that the axles can support. However not too high where the gears teeth get small enough to not be able to handle the sudden torque from the motor. Your transmission can support up to an axle gear ratio of like 10.0, but that's not possible obviously.
 
Interesting. I’ve been reading about those that have taken 4low to 30mph+ on this very forum. But yes it would be a very limited one time test.

It'll likely be fine for the one-time test. I just don't want anyone coming back to my post and saying, "see he said you can go faster than X" after blowing up their transfer case :LOL:

IIRC the manual says 25mph, not 10
Thanks for the correction!
 
The difference between 3.07 and 4.56 is about 0.67.
The difference between second gear and third gear is about 0.65.
So if you want to see almost exactly what regearing will be pick a speed like 35 miles an hour in third gear and floor it, then repeat at 35 mph in second. That's the difference you will experience. After regearing third gear will be an almost exact replacement for your current second but you will have two gears below that. You can absolutely test how it feels now without changing anything, upside of a manual.
 
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The difference between 3.07 and 4.56 is about 0.67.
The difference between second gear and third gear is about 0.65.
So if you want to see almost exactly what regearing will be pick a speed like 35 miles an hour in third gear and floor it, then repeat at 35 mph in second. That's the difference you will experience. After regearing third gear will be an almost exact replacement for your current second but you will have two gears below that. You can absolutely test how it feels now without changing anything, upside of a manual.

That’s a good call, thanks! Between that and testing how first gear might feel by using 2nd gear and 4low, I should be good to go!
 
Thanks for this perspective - very helpful. Especially the speedometer fix. I’m at some point going to need to just roll the dice and regear regardless of the different performance characteristics of the electric motor.

4.56 but I might keep my 31.5” tires until they are done, then go to 33”.

I might go dual motor which will be 350 ft-lbs of torque and 250HP so that would “solve” some problems too.

Here’s the chart showing what speedometer drive gear you need for your tire size & gear ratio. I suppose this would still work for an electrically powered TJ.

6277DC0F-250C-40A3-8924-EDDA155AFCA8.png
 
I found an electric jeep article with this paragraph.
I thought it was interesting.

It has up to 500hp and 425lbft of torque at the motor. I replaced the factory 9.38:1 gears in the drive unit with 4.5:1 gears. Those, combined with the 3.07:1 diff gears gives me a final drive of 13.8:1. That’s basically like being in 1st gear all the time. You can get away with this because the Tesla motor spins up to 16,000rpm! I should have a top speed of around 100mph and a 0-60 time around 5 seconds. The DU weighs 300lb. The 4cyl, 5 speed and transfer case weighed 660lb. Electric propulsion is dramatically more power dense than internal combustion. I’m using a full 90kWh battery pack from a Tesla Model S or Model X. It consists of 16 24 volt modules that each weigh just over 50lb. Combined with the battery racks, the battery adds over 1000lb to the Jeep. 90kWh is equivalent to 2.6 gallons of gas. 2.6 gallons of gas would weigh about 20lb. What weight I lost in the motor I gained back and more in the battery.

https://www.4x4setup.com/2021/07/24/jeep-tj-1997-with-a-tesla-engine/
 
I found an electric jeep article with this paragraph.
I thought it was interesting.

It has up to 500hp and 425lbft of torque at the motor. I replaced the factory 9.38:1 gears in the drive unit with 4.5:1 gears. Those, combined with the 3.07:1 diff gears gives me a final drive of 13.8:1. That’s basically like being in 1st gear all the time. You can get away with this because the Tesla motor spins up to 16,000rpm! I should have a top speed of around 100mph and a 0-60 time around 5 seconds. The DU weighs 300lb. The 4cyl, 5 speed and transfer case weighed 660lb. Electric propulsion is dramatically more power dense than internal combustion. I’m using a full 90kWh battery pack from a Tesla Model S or Model X. It consists of 16 24 volt modules that each weigh just over 50lb. Combined with the battery racks, the battery adds over 1000lb to the Jeep. 90kWh is equivalent to 2.6 gallons of gas. 2.6 gallons of gas would weigh about 20lb. What weight I lost in the motor I gained back and more in the battery.

https://www.4x4setup.com/2021/07/24/jeep-tj-1997-with-a-tesla-engine/

Interesting article! I’ve seen photos of that build but not the backstory.

I have 6 Tesla batteries - I am amazing he was able to fit 16 in his TJ. There are a couple of reasons I didn’t pursue this route:

1. I did not have the expertise (in fabrication, etc) or budget to pursue that build.
2. I wanted to keep my 6MT, you cannot do that with a Tesla motor for a variety of reasons.
3. That build is 400v, my system is 150v, so safer.
4. I wanted to keep weight distribution and scale the same as stock so not to have to do suspension work. I took out 700lbs of motor, exhaust, gas tank, and accessories and replaced it with about 600lbs, so went on a diet!
5. I wanted to make it so that anyone could drive it without any special instructions.

But yes, a 14:1 ratio would be great if I could spin to 16,000rpm smoothly and if I had all that HP and torque. But because I’m attached to the NSG370, I’ve limited my motor to 5500rpm even though it can go to 8000rpm. I cannot find any literature about if the NSG370 can rev higher without issue.
 
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Torque is the issue, with a max input rating of 272 ft/lbs my guess is that you are well into crazy town.

No I have a small electric motor rated at 176 ft/lbs. I might dual motor it to 352 ft/lbs but heard some LS are running this transmission no problems per Novak and other sources. No one talked about how high the transmission can REV though.
 
I wouldn't worry about 8k, that transmission is hooked to things that spin close to 7k from the factory so you're probably safe well beyond that. I think it's used with some modern V6 engines and they don't have the same limits the 4.0 does.