Help me decide between 3.91’s and 4.10’s

[acammer]

Great photos and comparison. It reminded me of a couple pictures this conversation may find interesting. On the left is the OEM differential, and 4.10 gears, and on the right is the G-Force 9" with 4.63 gears. The size difference of both the gears themselves and the assembly is pretty incredible. The weight too - the 9" added about 40lbs. The aluminum center would be lighter, but at this point we're going for ALL the bulletproof!

[Bow94z]

wow neat looking 4:63 gear

[acammer]

Originally Posted by Bow94z

wow neat looking 4:63 gear

Yea, 9" gears are wild looking. They use that super low pinion position, which creates that high hypoid offset and really makes the pinion teeth long and twisted. Awesome for strength, undesirable for efficiency.

[MitchRoyce]

Personally, I think you should go with the 3.91's. Since you're using your ride as a daily driver and you're not into drag racing or launching your car, the 3.91's should be plenty to give you a nice boost in acceleration and low-end power.

Don't get me wrong, the 4.10's would definitely give you some extra oomph, but they might be a bit overkill for what you're looking for. Plus, with the 3.91's, you'll still be able to maintain some decent gas mileage and not have your RPM's screaming at highway speeds.

[Bow94z]

I've been on the fence which is why i have both gearsets as i wait for my installer to free up his schedule.

I was initially going with 391s, but i think I've made up my mind and go with 4:10's.

I had 4:11's in my 4th gen M6 and loved them.

[acammer]

Originally Posted by MitchRoyce

Personally, I think you should go with the 3.91's. Since you're using your ride as a daily driver and you're not into drag racing or launching your car, the 3.91's should be plenty to give you a nice boost in acceleration and low-end power.

Don't get me wrong, the 4.10's would definitely give you some extra oomph, but they might be a bit overkill for what you're looking for. Plus, with the 3.91's, you'll still be able to maintain some decent gas mileage and not have your RPM's screaming at highway speeds.

The difference between 3.91s and 4.10s at 75mph is 100rpm. I wouldn't expect more than a few tenths of an MPG at that difference. If a few tenths of an MPG matter more than the performance, I would suggest that you may have the wrong vehicle.

[IWANTA(ss)]

I have a 1le that came factory with the 3.91 when I cammed it I went to 4.10 the rpm difference wasn’t noticeable on the hwy, cruising I got unbelievable gas mileage. 1st gear is fun lol but once I started do the driver mods she really got down 4.10 FTW

[acammer]

Originally Posted by IWANTA(ss)

I have a 1le that came factory with the 3.91 when I cammed it I went to 4.10 the rpm difference wasn’t noticeable on the hwy, cruising I got unbelievable gas mileage. 1st gear is fun lol but once I started do the driver mods she really got down 4.10 FTW

People sleep on 4.10s in 1LE's, and I think that's a mistake. They are a perfect candidate for 4.10s, which helps get back some of the better aggression the regular SS cars have in 1-2-3, puts 4th in a pretty good place for the drag strip, makes 5th a little shorter but still has plenty of speed, and 6th is still a huge overdrive that keeps RPM super chill on the highway. I love that you did it!

[IWANTA(ss)]

Originally Posted by acammer

People sleep on 4.10s in 1LE's, and I think that's a mistake. They are a perfect candidate for 4.10s, which helps get back some of the better aggression the regular SS cars have in 1-2-3, puts 4th in a pretty good place for the drag strip, makes 5th a little shorter but still has plenty of speed, and 6th is still a huge overdrive that keeps RPM super chill on the highway. I love that you did it!

You were the reason I pulled the trigger still watch your shifting vids b4 I hit the track for inspiration

[Bow94z]

Got my 410's installed today and very pleased so far. acammer also pushed me to 4:10's as I had already purchased 3:91's then changed my mind.

Motive 4:10's
Eaton TruTrac
Hendrix Solid rear cradle bushings
BMR non adjustable Toe rods and Trailing arms (with outer bushing)

Drove about 10miles so far, gears and Trutrac are quiet. I also had a very good installer put them in. He has a good reputation with gear installs.


Apparently my 3:45's are trashed as there is a alot of wear on them. I want to pull them out and look at them later. I had an axle seal leaking and ran the rear somewhat dry and there was a bunch of shavings in the housing. There was also alot of play so that could also be a factor.

[Joe.G]

Glad to hear you like them, if I was to do it over again I'd probably go 4.10 but overall I am happy with the 3.91. when you get a chance can you get the car up in the back and let me know how much you can spin wheel forward and backwards before drive shaft starts to move. Also make sure you change the oil in 500 miles I think you'll be surprised how bad it looks.

[bstromback2002]

I just installed 4.10 and a speedmaster torq worm and I’m also pretty happy with my decision. I wasn’t sure if it was going to be too much for a daily but it’s a blast.


Sent from my iPhone using Tapatalk

[Ck1984]

How do i find out what gears i already have?
is it in the vin?
or a specific code to look for on build sheet?

[acammer]

Originally Posted by Ck1984

How do i find out what gears i already have?
is it in the vin?
or a specific code to look for on build sheet?

Based on the year, model, and transmission type you should be able to determine what you have. You appear to have an automatic 2015 2LT - that should have 3.27 gears. All of the automatic V6 and L99 V8 cars had 3.27s, with exception to the 2LS trim level, which had 2.92 gears.