Turbocharging a BMW M20 engine

This page describes the various paths that can be followed in the process of turbocharging a BMW M20 motor, from mild to wild. Most of the information pertains to the M20B25 2.5litre version.The information is arranged thematically, with no guarantee of its accuracy.

Engine block

The BMW M20 motor comes in various flavours: Stock internals have been proven to be reliable at high output levels, with the rods being the weak link if detonation is avoided. At elevated power output, detonation will be unforgiving towards the stock cast pistons. Various options to use for the bottom end are:

Listed below are the dimensions of some pistons and rods that can be mixed and matched to get various displacements in an M20:

One documented setup is:
Another documented setup:
Use some simple mathematics to determine if your piston/rod/crank combo will fit inside the block, and then start worrying about piston shape (for valve reliefs and compression ratio's sake).

Cylinder head



Engine hardware


Intake manifold



Exhaust manifold



Turbocharger




Fueling

The engine can be fueled in an infinite number of ways, but the recommended paths are:



Ignition

Most modern vehicles have very good ignition systems, and the BMW is no exception. Some recommendations: