Differential Time, 3.91 vs 4.10 on 6 speed ZCP

[maupineda]

Also it has to do with the geographic characteristics of where you drive. In the US where everything is flat I guess stock gears maybe fine, where I am, you rarely can do 100mph, our roads are very steep and curved, so shorter gearing make the car so much better

[Anri]

So! before I spend $5000 plus

Hi,

Could you please share what is the reason for you to change the stock diff ?
What purpose/s are you after ?

Regards,
Anri

[Silbergrau metallic]

Hi,

Could you please share what is the reason for you to change the stock diff ?
What purpose/s are you after ?

Regards,
Anri

My rear differential has developed a whine and my friends shop has determined that it's coming from it.and needs to be rebuilt. I was considering just going stock, but the purpose of this thread was to see what other members opinions were about changing the gearing for a performance gain from stock and if there was a better option other than the stock BMW LSD. I've read a few threads that stated going 3.91 or 4.10 was one of the best mods they've done to their cars, but have also read a few negative ones also, but didn't read a reason for them not liking it. I have no reservations about sticking to the stock 3.62 gearing as I'm very satisfied with the acceleration of my Car, but! if I can make it even more exciting to drive, then I wanted to do some more research as to what other members on this board have done and what LSD they went with and why.

[Obioban]

Also it has to do with the geographic characteristics of where you drive. In the US where everything is flat I guess stock gears maybe fine, where I am, you rarely can do 100mph, our roads are very steep and curved, so shorter gearing make the car so much better

Lol. The US is not flat everywhere 🙄

[natty99]

Bottom line, it's subjective. I have the 3.91 gears and love them. The bump in cruising RPM (at 80-90 mph) was not a problem as some report, but I do think it's near the cusp of being tolerable. For predominantly highway driving, I think the 3.91s are as much as I would want to go. In the city, or certain track work, I can see value in the 4.10s. But again, that's my personal take on it. I, too, find the stock gears a bit too tall.

[Obioban]

My track only M3 came with 4.10s, and I moved it back to stock. I found the constant shifting annoying and slower.

I love the stock gearing on track. You’re overwhelmingly in 3rd and 4th, which don’t require any sideways force to shift into— so no risk of money shifts.

On the rare occasion there’s a super slow speed corner that needs 2nd gear, I wouldn’t want it to be any shorter.

[bigjae46]

If you have a loud exhaust and street drive it...a shorter diff is going increase the revs and noise. Something to consider. You will certainly notice the difference with a 3.91. But 3.91 vs 4.10 for street isn't that different and likely won't matter with a 6 speed.

For those that swapped in 5 speeds (like me), this is more of a critical decision because there is a trade off in top speed.

If you have an SMG and plan to keep it SMG, it's an easy decision. Go with a 4.10 because paddle shifting.

[STAATS]

I went with 3.91 as I was rebuilding my diff and installing a Drexler Motorsport core... it was very much a "while I'm here" type change as if I didn't do it then I would never do it.

It's hard for me to fully capture my thoughts as I need a proper custom tune (imminent) to fully asses, but in general I liked it early on, although my car had been off the road for ~2yrs and had a shopping list of mods and an engine rebuild so its hard to nail down individual changes.

Over time I have moved to the fence... part of my likes it, its a bit more lively and thats fun, but part of me also thinks it was pointless... the increased revs at slower speeds around the street is off putting for my wife and over time can feel obnoxious putting around the streets. I will reserve my full assessment for when I get a proper custom tune and finally get to start hitting the track... I do believe it will come into it's own when i enter Tarmac Rally events but until then I'll stay on the fence... I don't like it enough to advocate for it, yet I also don't dislike it enough to not advocate for it or consider removing it.

I would say if you are on the fence its worth saving your money and spending it elsewhere... I feel like unless you are tracking the car and feel like you are missing corner exit torque and feel like that is something that would support your driving style or the tracks you drive on then its potentially not worth it but thats just a thought.

[sc_tr0jan_m3]

I’m working w a shop to swap in a 5 speed and 4.10 for my track car. Kinda excited to see how it compares. I went with their recommended setup that they run on their shop cars.

I had a buddy who tried 3.91 with a 6 speed and he said he didn’t like it… def appears to be a personal preference thing. He said he’ll be doing a 5 speed with 4.10’s.


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[cobra]

I think stock gearing is already pretty low. First gear is so damn low. I've heard a lot of people regret their 4.10's because it makes first gear useless.

[ZiMMie]

There is also an option for a 3.73 and a 3.85.

[old///MFanatic]

My track only M3 came with 4.10s

Well to be fair, if I’m not mistaken you’ve disclosed before that was an E36 M3 that BMW M fits stock with the 3.15 ratio. Going to a 4.10 would be a gear change of 30% on an E36. Agreed that’s a big jump.

[Slideways]

Not sure how true this is, but a shop tech said that the 4.10s make more gear whine than the 3.91s because the gears are cut straighter. I think the 3.91s would be nice for a street car that sees a lot of uphill twisty roads. In 2nd gear, the revs can sometimes fall to 2k rpm on those slow, uphill, tight turns.

[sapote]

Not sure how true this is, but a shop tech said that the 4.10s make more gear whine than the 3.91s because the gears are cut straighter. .

I believe this is true. The 4.10 must have a smaller pinion diameter, and so the pinion/ring helical teeth cannot have the same angle as the lower ratio gears.

[Silbergrau metallic]

I swapped out my LSD for a wavetrac, but kept final drive ratio stock. BMW just perfectly nailed it with the stock gearing, IMO.

From what I've read, I think I'm going to stick with the stock gear ratio, Curious! you're very knowledgeable about E46 M3's, what was your reason for going to the Wavetrac LSD and is it a much better option to the stock LSD and did you notice anything you disliked about Wavetrack compared to stock, because I want to Buy Once and Cry Once, even if it's more expensive to go with the Wavetrac LSD option.