Strom B48 / B58 Alternator Overrun Pulley
STROM BMW B48 / B58 Alternator Overrun Pulley
Upgrade your BMW’s accessory drive system with the STROM Motorsports B48 / B58 Alternator Overrun Pulley, designed to allow the alternator to freewheel when the engine is decelerating.
Unlike a conventional fixed alternator pulley, the overrun design helps isolate the alternator’s rotating mass during rapid engine deceleration. This reduces unwanted load on the accessory drive and crank balancer, while helping the engine operate more smoothly and respond more effectively during gear changes.
An ideal upgrade for BMW B48 and B58 performance builds, including modified road cars, engine swaps, track cars and motorsport applications.
The B58 Gen 1 and S58 pulleys should be available Sept 22nd.
Early B48 Mini Cooper, S54, S65 and S55 pulleys in development.
The Alternator Overrun Pulley for the B48 / B58 allows the alternator to freewheel when the engine is trying to decelerate. This has many benefits. It saves your crank balancer from trying to tear itself apart and also makes the engine run smoother and shift more rapidly. See video below for in depth explanation.
Fitment:
There is an incredible amount of crossover between models and engines and alternators. We have provided a list of what we know it fits but its impossible to correlate them all. The best way to guarantee fitment is to check if your current alternator has a 22mm nut holding the stock pulley on. Usually this nut is covered by a black plastic cap as shown in the pictures. If your pulley nut has not cap and is 24mm then this part will not fit. The part that will fit your car should be released by late September.
Also it seems that in most cases if you have a factory Denso alternator this part will fit. If you have a factory Bosch alternator this will not fit.
Feel free to email us with your full VIN to info@strommotorsports.com.
If your car already has an aftermarket alternator then there is no way to verify other than by checking the nut size.
This pulley fits the alternators listed below if they are an OEM or factory alternator. Alternator part numbers listed are not comprehensive and are often on multiple engines and models.
Gen 1 Inline Engines
|
Engine codes |
OE alternator part numbers |
Example chassis |
|
B38 B46 B48 |
12318645325 12318645326 12318645329 12318648045 12318648046 12319845492 |
F20 1 Series F22 2 Series F30 3 Series F32 4 Series |
Gen 2 (TU) Inline Engines
| Engine codes | OE alternator part numbers |
Example chassis |
|
B46D B47B B47D B48C B48D Gen 2 B58TU B58C B58D |
12318634166 12318634167 12318654280 12318689832 |
Toyota Supra 2020+ G20 3 Series G22 4 Series G30 5 Series G32 6 Series G42 2 Series G29 Z4 G01 X3 G02 X4 G05 X5 G06 X6 |
Gen 2 (TU) transverse engines
|
Engine codes |
OE alternator part numbers |
Example chassis |
|
B36C B37B B38B B38C B46C B46D B47B B47D B48D B48E |
12318627125 12318632398 12318680374 |
F40 1 Series F44 2 Series F48 X1 F39 X2 F54 / F55 / F56 Mini |
Not sure which alternator you have? Send us your VIN and we'll confirm the correct pulley before you order.
THIS PART DOES NOT FIT (But STROM are working on parts for these):
- First Gen B46 / B48 and B36 in Mini / X1 / X2. Example alternator part numbers are: 12319845487, 12317646814, 12317640875. The pulley on these alternators is very short and does not have a shaft spacing out the pulley as seen on the new part.
- Most First Gen B58. We know it will not fit alternators of the following part numbers: 12318571357, 12318571358, 12318614276, 12318614278.
- S58
- Does not fit any car with a 48V alternator 12318490540 - also known as Mild Hybrid.