For most Stage 0.5-1.5 M50, an upgraded drop-in filter is usually perfectly fine and offers a similar power gain to a full intake system. At higher power levels, upgrading the intake system will be more worthwhile.


The stock exhaust manifold is relatively good for OE. Upgrading this component is still a worthwhile investment, and can reduce weight, temperatures, and increase overall engine efficiency.

A cat-back exhaust offers the least gains in comparison to intake and exhaust manifold. 57-76 mm (2.25-3 inch) diameters are ideal, though there is minimal difference beyond 65 mm (2.5 in) diameter at lower modification levels. Please consider the weight difference to power gain and decide what works best for you.



Read the camshaft page for more information.


+1 mm oversized valves are a worthwhile upgrade. If you plan to rev high, the most important upgrades are valve springs and rockers.






Early M50B20 and all M50B25NV (Non-VANOS) were equipped with Motronic 3.1 ECUs.

1994-1995 M50 and S50B30 engines were equipped with Motronic 3.3.1 ECUs. Major updates include VANOS control


The stock injectors on all M50 variants (B20, B25NV, B25TU, and including the S50B30) are 17.5 lb/hr @ 3.5 bar. These support 180 WHp safely, with an absolute maximum of around 210 WHp.

As you go beyond 180 WHp, it becomes critical to upgrade the injector flow rate. 19 lb/hr injectors will support 200 WHp. 24 lb/hr injectors will support 245 WHp. 42 lb/hr injectors will support 430 WHp.

Read more about injectors!

Fuel Pump

The stock M50 fuel pump in all models is 160 LPH and supports over 300 WHp. It is not necessary to upgrade this until you approach or surpass 300 WHp. In fact, it is recommended very highly to leave this stock until necessary to upgrade.

Forced Induction

You can expect between 6-12 Hp per pound of positive pressure added for most forced induction setups. All M50 variants are able to handle 6-8 PSI relatively well without any internal modifications. With just ARP head studs and a quality head gasket, an otherwise stock M50 can handle 12-15 PSI relatively well.

A tuned Motronic 3.1/3.3 ECU can handle 450 WHp relatively well without any sensor changes or large modifications.

The B25NV MAF (Mass AirFlow Meter) is scaled to handle a maximum of about 280 WHp.

The B25TU MAF is scaled to handle a maximum of about 330 WHp.

A common upgrade is the M60 MAF, which is scaled to handle nearly 400 WHp.




Used in 1991-1993 E36 325i and E34 525i vehicles.

Colloquially known as the M50B25NV, this model is not equipped with VANOS.


Used in 1993-1995 E36 325i, and 1992-1996 E34 525i vehicles. In the United States, it was used only in 1994-1995 E36 325i and E34 525i vehicles.

Colloquially known as the M20B25TU or M50B25TUB, this model is equipped with VANOS.