Gearing

FallCityJeepster

Well-known member
Founding Member
Joined
Jan 18, 2021
Messages
100
Reaction score
118
Location
Fall city, wa
The 392 comes stock with 3.73 instead of the standard Rubicon JL of 4.10. Almost all advice points to regearing for larger tires to 4.88 or larger if going big.

Was 3.73 used simply for acceleration?

Does that mean 4.10 should be used for 37” tires instead of typical guidance if 4.88?
 
Gearing just gets you back what you loose when going with a bigger tire. With a 392 having so much TQ it will be less affected by a tire size change than the smaller motors.

I'm sure they selected 3.73 for a couple of reasons. They don't want to break axles and since it has so much TQ they can run 3.73 and keep the MPG up as much as possible, 4.10:1 applies more tq to the axle than a 3.73, 4.88.1 more than 4.10:1 and at some point things break from stress.

This is most likely one of the reasons they went with the 2.72:1 4 low, That and they wanted to use the 4 auto case so the power is spread across two axles and the average guy can keep these in a straight line. Remember these have factory warranty so I'm sure a lot of that plays into gear ratios.

I have twisted shafts on a JK 44 with the 3.8 "minivan" motor running 4:1 case with 4.88:1 gears. Its easier than one might think. I now run a Dana 60 on that one.
 
Gearing just gets you back what you loose when going with a bigger tire. With a 392 having so much TQ it will be less affected by a tire size change than the smaller motors.

I'm sure they selected 3.73 for a couple of reasons. They don't want to break axles and since it has so much TQ they can run 3.73 and keep the MPG up as much as possible, 4.10:1 applies more tq to the axle than a 3.73, 4.88.1 more than 4.10:1 and at some point things break from stress.

This is most likely one of the reasons they went with the 2.72:1 4 low, That and they wanted to use the 4 auto case so the power is spread across two axles and the average guy can keep these in a straight line. Remember these have factory warranty so I'm sure a lot of that plays into gear ratios.

I have twisted shafts on a JK 44 with the 3.8 "minivan" motor running 4:1 case with 4.88:1 gears. Its easier than one might think. I now run a Dana 60 on that one.
Thanks for the info.
 
Back
Top