Differentials - 3.62 - 3.91 - 4.10

[oceansize]

Diff weighs 82lbs sans fluid and cover. Weighed 2 back to back both 82lbs. Not to be pedantic, Oceansize, but in case someone is creating a shipping label. With fluid and cover it must be 90?

I couldn't remember exactly in what state I weighed it, or whether I weighed the 3.91 or the 3.62, so I wouldn't argue what you wrote. I meant to write it down as I have a $500 wrestling scale which is super accurate (son wrestles so we have to be on point after weight cuts).

[bigjae46]

It depends on your tires. If you run Hoosiers or similar R-comp tires, the outer diameter is smaller than normal.

So a 4.10 will be fine with stockish size tires but will be too short if you run shorter r-comp or slick.

I have a 3.73 which is a little shorter. I plan to run a 245/40R17 Hoosier or BFG R1. They are 24.3” OD so it gears it like a 3.91.

My buddy has a 4.10 and we both run NT01s. He pulls on exit out of every corner. I have to close the gap under braking and to the apex. You can really see the difference when we go into the front straight. Pulls a couple of car lengths on me.

https://youtu.be/-0nocBzIn-E

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[SandeepM3]

There is pretty much no argument that on a track that you don't see 6th that 3.91 is not better vs. 3.62. Every second you are in 5th you are higher in the power band. Now gearing in general is highly dependent on what kind of corners you have. I also find that once you have slicks and aero on an e46 2nd gear is just about useless even with stock gearing - so that puts you more into the power band in 3rd on corner exit.

Really depends on the track. I literally just went through every turn and straight and through my speeds at each to see what gear and rpm I would be in for each gear set. Its looking like a 3.91 for me. Its either 3.91 or 3.62, but definetly not the 4.1 for my home track.

[Arith2]

It depends on your tires. If you run Hoosiers or similar R-comp tires, the outer diameter is smaller than normal.

So a 4.10 will be fine with stockish size tires but will be too short if you run shorter r-comp or slick.

I have a 3.73 which is a little shorter. I plan to run a 245/40R17 Hoosier or BFG R1. They are 24.3” OD so it gears it like a 3.91.

My buddy has a 4.10 and we both run NT01s. He pulls on exit out of every corner. I have to close the gap under braking and to the apex. You can really see the difference when we go into the front straight. Pulls a couple of car lengths on me.

https://youtu.be/-0nocBzIn-E

Sent from my iPhone using Tapatalk

He's definitely pulling away quickly. Power mods and tune similar?

[Apex_80]

Eh... If you're in 5th gear with 3.91s vs higher RPM 4th gear with 3.62s at the same speed, the 3.62 car is making more power AND has a more aggressive total gear ratio at that speed-- plus the time you're shifting instead of accelerating.

One of the best mods we did to the dedicated race car we owned for a while was move it from the 4.10s it came with to the stock 3.62s.

I agree 4.10 is the wrong option. I am referring to straightaways that you see 5th gear with both rear gear ratios. Anyways, it's personal preference I suppose but corners like turn 7 Road Atlanta and 11/12 at VIR stand out as 3.91s being the better option as you don't want to go down to second but third lugs a bit. Seems to be a lot of corners in that speed range where 3.62 lugs a little.

[Rudbari]

I love my 3.85 gears (e9x m3 manual ring and pinion), but I mostly drive on curvy back roads rather than on the track.

Bro if you own 3.85 final ratio , I would like to ask you in 60-130 pull how many time you shift .

when I was 4.10 I used to shift 2 times ( 3rd to 4th then 4th to 5th ) as it was to short . Now with 3.62 it’s one shift 3rd to 4th .

I would like to know about 3.85

[rbg]

I have one question. How do you guys spin wheels on stock e46 m3? 🤔😀

[Apex_80]

I have one question. How do you guys spin wheels on stock e46 m3? 🤔😀

Bad tires

[STAATS]

I have one question. How do you guys spin wheels on stock e46 m3? 🤔😀

Diesel drips...

[yhp2009]

I have one question. How do you guys spin wheels on stock e46 m3? 🤔😀

Sport button

[bigjae46]

He's definitely pulling away quickly. Power mods and tune similar?

He probably had a little more power (intake, pulleys, tune) vs me (BW exhaust, no tune) but the cars were pretty even.

Even now that I have more power, aero and a lot less weight, I don’t run him down on exit. Yeah you shift more but it’s easier to stay in the power band especially on slower corners with a 4.10.

Then I can shift into 2nd but then the car runs a lot hotter.

From a numbers point of view, a 4.10 doesn’t guarantee an improvement depending on the track

From real world, I say it makes a big impact.

None of us can say that a 4.10 causes an up shift whereas a 3.91 will not. None of us are that consistent. If you’re basing that on your data then you’re artificially limiting yourself to a certain speed in a corner.


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[Obioban]

He probably had a little more power (intake, pulleys, tune) vs me (BW exhaust, no tune) but the cars were pretty even.

Even now that I have more power, aero and a lot less weight, I don’t run him down on exit. Yeah you shift more but it’s easier to stay in the power band especially on slower corners with a 4.10.

Then I can shift into 2nd but then the car runs a lot hotter.

From a numbers point of view, a 4.10 doesn’t guarantee an improvement depending on the track

From real world, I say it makes a big impact.

None of us can say that a 4.10 causes an up shift whereas a 3.91 will not. None of us are that consistent. If you’re basing that on your data then you’re artificially limiting yourself to a certain speed in a corner.


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More accurately, it's sometimes faster sometimes slower, depending on the speeds possible in a given area-- both in the real world and from numbers. If you have to shift into a higher gear because you're running a more aggressive diff, you have a less aggressive net gear ratio and lose time to shifting. If a 3.62 and 4.10 car end up in the same gear in a given area, the 4.10 car will have no extra shifts required and a more aggressive net drive ratio.

[old///MFanatic]

I currently am sitting with a stock diff and considering going to a 3.91 car is N/A.
Curious whether anyone has done the swap on here and your thoughts.
How is the driving experience/improvement? Butt dyno/fun dyno... Costs? Where can you get it swapped Diffs online?

Here is another previous thread on the topic.
https://nam3forum.com/forums/forum/m...870-4-10-gears
(post 38 shows some comparisons)

Understand that there are quantitative changes that can be measured which you can base your decision on( I find this the best way).
Then there are opinions/personal preference.
And opinions based on the quantittative changes.

The decision is based on what YOU desire to achieve in gains vs changes. Example is the change for some on a street car is going to be different from someone who uses mostly for track. So using advice based on someone else’s preference really does not help you unless you’re desired outcome is the same.

With that said I love BMW Motorsport’s 4.10 gear swap. The torque multiplication is wonderful.

[jvit27]

I installed a 3.91 a few months ago. I only have headers+tune+19" wheels. It woke the car up and it's definitely more fun/lively on the street -however- my car is SMG so if i'm being completely honest, it's just a bit of a band-aid for not being a manual...

That being said I like it but I don't love it. No regrets trying it but it won't stay in my car either. It's not a huge compromise in the grand scheme other than highway cruising, so some people will be ok with that but it matters to me. Cannot imagine going 4.10 i'd hate it. The intangible effect of the car being a bit less relaxed at 85-90mph and more E36-like feels like a downgrade IMO. It definitely traded away some signature S54 character for how long you can run the gears out.

Not a terrible mod but i'd wholeheartedly insist putting the car on a 250lb diet instead is a better decision.

[M3mike]

I installed a 3.91 a few months ago. I only have headers+tune+19" wheels. It woke the car up and it's definitely more fun/lively on the street -however- my car is SMG so if i'm being completely honest, it's just a bit of a band-aid for not being a manual...

That being said I like it but I don't love it. No regrets trying it but it won't stay in my car either. It's not a huge compromise in the grand scheme other than highway cruising, so some people will be ok with that but it matters to me. Cannot imagine going 4.10 i'd hate it. The intangible effect of the car being a bit less relaxed at 85-90mph and more E36-like feels like a downgrade IMO. It definitely traded away some signature S54 character for how long you can run the gears out.

Not a terrible mod but i'd wholeheartedly insist putting the car on a 250lb diet instead is a better decision.

This was the answer I was looking for. Thank you