Winter Project: Diff Refresh

[eacmen]

So I have a dedicated HPDE M3 w/SMG. The clutch packs in the LSD seem to be getting tired (104k miles). Considering two mods:

1. 3.85 or 4.10 final drive ratio
2. LSD refresh or completely new unit.

The options at diffsonline are sort of overwhelming and pricey. My major questions are:

1. Does SMG handle change in final drive well? If so any instructions on how to code it?
2. Should In just rebuild the factory LSD or go with an aftermarket unit. Not looking at chasing hundredths here, just want something that is predictable.

Thoughts?

[oceansize]

The coding is super easy via ecuworx. Just make sure the final drive u go with is present as an option, I can’t remember what was available. I’m on 3.91 via diffs online. No issues.

[eacmen]

The coding is super easy via ecuworx. Just make sure the final drive u go with is present as an option, I can't remember what was available. I'm on 3.91 via diffs online. No issues.

so the final drive coding is in the engine ECU not the SMG ECU?

[oceansize]

so the final drive coding is in the engine ECU not the SMG ECU?

Yes assuming there isn’t something I’ve forgotten as it has been years. Regardless the ecuworx tool will handle.

[heinzboehmer]

Supposedly there's some SMG ECU changes needed as well: https://nam3forum.com/forums/forum/s...t-continuation

[oceansize]

Supposedly there's some SMG ECU changes needed as well: https://nam3forum.com/forums/forum/s...t-continuation

I remember that thread now. I never did find concrete evidence that was the case. The issues people reported were related to auto mode and the ecuworx tool fixes that.

[OldRanger]

I recently installed one of the Diffsonline 3-clutch limited slip with 35/60 ramped carrier in a car that’s basically dedicated To track use. I choked on the cost as well…so I opted to stick with the original 3.62 ratio and avoid premium pricing on that part of the spec. Traction being the goal.

Years ago, I installed one of their differentials with the OEM-style LSD in a car that sees road use.

I can confidently recommend the clutch type limited slip carrier for track. The traction is so good, there’s only one drawback I can see: you might actually be disappointed in how it neutralizes any mild oversteer you might have intentionally ‘tuned’ into your car.

[S54330Ci]

Diffsonline suggests a 3.85 ratio for SMG cars.

In my S54 powered track car (330Ci) I recently installed a 3.91 with 3 clutch (30/90) ramps and it really wakes the car up. Much better pull out of corners and keeps the engine in the power band better than the standard 3.62. The downside (with my 5-speed) is the engine does spin faster at freeway speeds, however since this is a track car it only sees the freeway to / from the track. The trade-off was totally worth it.

[eacmen]

Diffsonline suggests a 3.85 ratio for SMG cars.

In my S54 powered track car (330Ci) I recently installed a 3.91 with 3 clutch (30/90) ramps and it really wakes the car up. Much better pull out of corners and keeps the engine in the power band better than the standard 3.62. The downside (with my 5-speed) is the engine does spin faster at freeway speeds, however since this is a track car it only sees the freeway to / from the track. The trade-off was totally worth it.

Any idea why SMG should use 3.85?

[OldRanger]

Any idea why SMG should use 3.85?

It costs more.

[S54330Ci]

Any idea why SMG should use 3.85?

Best to ask Diffsonline as that was their recommendation.