B48 / B58D Alternator Overrun Pulley

Backorder update - we expect to be shipping out to current backorders Sept 8th. If you order now it should ship around Sept 10th. The B58 Gen 1 and S58 pulleys should be available Sept 22nd.

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. Longer writeup coming soon. 

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 PART DOES NOT FIT (But we 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. 

Installation Instructions