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.

Key Features

• Alternator overrun pulley for BMW B48 and B58 engines

• Allows the alternator to freewheel during engine deceleration

• Helps reduce stress on the crank balancer

• Promotes smoother engine operation

• Helps improve engine response during rapid gear changes

• Fits all B48 and most non-48V B58 alternators

• Compatible with selected B38 and transverse B48C applications

• Ideal for performance, track and engine-swap applications

BMW B48 & B58 Fitment

Designed to fit all B48 and most B58 engines using a non-48V alternator.

Known compatible alternator applications include:

• 12318634167 – B48 and B58D applications, including models such as the BMW 330i and 340i

• 12318627125 – F56 MINI and other transverse B48 applications

The pulley can also fit the alternator used on the B48C transverse engine found in MINI models, as well as certain B38 applications. Due to the number of engine and chassis variations, compatibility should be confirmed before ordering.

Important B58 Fitment Information

Some early BMW B58 alternators use a different pulley design. If your factory alternator pulley is secured with a 24mm nut rather than a 22mm nut, this pulley will not fit.

It is also not compatible with alternator part numbers:

• 12318571357

• 12318571358

• 12318614276

• 12318614278

Please verify your alternator or original pulley configuration before purchasing.

Performance Upgrade for BMW B48 & B58 Engines

Whether you're upgrading a tuned BMW, building a B48/B58-powered track car or completing an engine swap, the STROM Motorsports BMW B48 / B58 Alternator Overrun Pulley is a purpose-designed upgrade for reducing accessory-drive stress and improving drivetrain refinement under deceleration.