BMW E30 Differential Ratio Guide

If you're swapping the drive train in your RWD BMW you will likely want to swap out the rear differential to one with a ratio that suits the transmission and your driving characteristics. BMW offers tons of OEM LSD options that are compatible across multiple chassis, requiring nothing more than a simple diff cover and output shaft swap. Differential gear ratio represents the number of times the driveshaft will rotate for each turn of the wheels. So if you have a 4.10:1 gear ratio the drive shaft turns 4.10 times for every turn of the wheel.  Generally, a longer ratio such as a 2.93 is suited for higher horsepower builds or street cruisers that desire a higher top speed with less engine RPM or better fuel economy.  A short 4.10 ratio will be better suited for rally cars and underpowered vehicles and give the sensation of better acceleration while sacrificing top speed, highway driveability, and fuel economy since it is turning more RPMs at higher speeds.  

E30 Diff Swaps

The E30 is becoming one of the most swapped chassis in the world with powerplants easily capable of producing 1000+ HP. An OEM BMW medium case differential will handle gobs of horsepower but its breaking point will ultimately depend on how much torque your setup makes.  We recommend our secondary diff mount for high horsepower setups to prevent any unnecessary twisting and deflection of the differential under heavy load.   

(M)=manual transmission (A)=automatic transmission *=Rare/hard to find/euro only

E30 84'- 93'

Medium Case Only (many options available from factory by special request)
318i/is (M42)  4.10 (M) 
318ic (M42) 4.27 (M)
325e before 9/85 2.79 (M)  
325e/es 2.93 (M) 
325i/is/ic 3.73 (M) 4.10 (A)
325ix - 3.91 (M)* 4.10 (A) 
M3 - 4.10 (M) 3.15 (M)* 3.25(M)*

E36 90' - 00' 

325i/is - 3.15 (M) 3.19 (A)
318i/is - 3.45 (M) 4.45 (A)
325ic - 3.15 (M) 3.64 (A)

M3 - 3.15, 3.23 (A/M) 

E28 81' - 88'

528e - 2.93 (A) 3.25 (M)
535i/is - 3.25 (M)
M5 - 3.91 (M) 

E34 87' - 96'

525i (M20) - 3.73 (M) 3.75 (M) 4.10 (A) 
525i (M50) - 3.23 (M) 4.10 (A) 
525it - 4.10 (A) 
530i - 3.07 (M) 3.15 (A)
530it - 3.23 (A)
535i - 3.46 (M) 3.91 (A)  4.27 (A)
540i - 2.93 (A)
M5 - 3.91 (M)* 3.73 (M)* 

E24 76' - 89'

Pre 88' 635csi - L6 3.46 (M) 
88'-89' - 3.64 (M) 3.91 (A)
M6 3.91 (M)  

E23 77' - 86'

735i - 3.46 (A) 3.25 (A)

E32 86' - 94'

735i/il - 3.64 (M) 3.91 (A) 4.27 (A) 
740i/il - 2.93 (A)
750i/il - 3.15 (A) 3.64 (A) 

E31 90' - 99'

850 - 2.65 (M) 3.64 (A)

E46 97' - 06'

323 all models - 3.46 (A) 3.07 (M)
325i/ci - 3.46 (A) 3.15 (M)
325xi - 3.23 (M)* 3.46 (A)
330i/ci/xi - 3.38 (A) 3.07 (M)
330 zhp - 3.07 (M)
Z4 2.5 - 3.64 (A)*
M3 - 3.62 (M)

E39 96' - 03'