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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > 3.07 to 3.15 diff swap for 325i



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      01-02-2022, 11:04 AM   #1
BrodieH
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3.07 to 3.15 diff swap for 325i

Hi, i have a 2010 e90 325i and am planning to convert it to a 330i. I was considering swapping in the diff from a 330i, which would change the ratio from 3.07 to 3.15. Hs anyone done this before? Is there any real benefit to this, or is it not worth the effort? Its not too difficult, all i need is the differential itself and a 330i propshaft.
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      01-02-2022, 01:07 PM   #2
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In my opinion not worth it. What would be worth it is swapping in the higher ratio diff from an automatic 325i or 330i. This is called the “poor man’s supercharger” due to the torque gain and increased acceleration.

Swapping to a 330i diff you may find the half shafts are splined differently, which would make the swap much more involved. I would stick with the 325i automatic diff to keep it simple and increase performance.
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      01-02-2022, 09:29 PM   #3
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3.07 to 3.15 is a very small difference. I wouldn't put time and money for such a small difference.
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      01-19-2022, 12:39 PM   #4
e90yyc
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As others have said: Probably not worth it.

I don’t know what ratios are available in your market, but what you’re proposing is only a 2.6% difference.

For there to be a worthwhile difference, in my opinion, you’d need to step up by a minimum of 10%, or if you’re like most folks and want a more pronounced change, 15% higher or more. A common “upgrade” in the NA market is to swap out a RWD 6MT 3.23 diff with a 3.91 diff from an AT xDrive car. That’s about a 21% change. Or if you have a 6MT xDrive car, you could move from your 3.38 up to 3.91; roughly a 16% change.

Though I’m sure people have done it, I don’t see as much of a point in going from the 3.73 to the 3.91, or from the the 3.23 to the 3.38. And even less of a point in doing what you’ve asked about.

On the other hand, maybe there’s something to be said for going subtle—I dunno. (I still maintain that what you’ve proposed it too subtle though.). In my case, I swapped a 6MT into my xDrive car, so I have 3.91 diffs where a factory spec would have 3.38. Yeah off-the-line performance is great, but I’m running over 3000 RPM on the freeway and first gear is so god damn short that I have to shift mid intersection after about one second of driving. I often just start in second.

Sooo, my long-winded point is that whether it’s even something you’d want to do depends entirely on your driving style. If you could move up to something like a 3.38, then it might be worth the time and effort.

Good luck!
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