Turbocharging a BMW M30 motor

Turbocharging a BMW M30 engine

This page describes the various paths that can be followed in the process of turbocharging a BMW M30 motor, from mild to wild. The information is arranged thematically, with no guarantee of its accuracy.

Engine block

The BMW M30 motor comes in various flavours:

M30B28, 2.0 litre, 75mm stroke, 81mm bore,140mm rods
M30B32, 2.5 litre, 75mm stroke, 84mm bore,135mm rods
M30B35, 2.7 litre, 81mm stroke, 84mm bore, 130mm rods
Connecting rod dimensions for M30:

C-C length: 135mm
Big end bore: 52.0mm
Big end width: 24mm
Pin diameter: 22mm
Small end width: 24mm

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:

Stock rods and pistons in various combinations,
Stock rods and pistons, with 3.5mm metal headgasket, will lower the compression by approx 1 point
Aftermarket forged steel rods, with forged aluminum pistons.

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

Pistons:

VW aircooled (69mm stock stroke) mahle forged piston, 90.5mm bore, 39.6mm CH
VW aircooled (82mm stroker) mahle forged piston, 90.5mm bore, 34mm CH
S14B23, 32mm CH, 92(?)mm bore
S14B25, 30.22mm CH, 95.5(?)mm bore

Crankshafts:

M30

Rods:

M30

Block:

M30, deck height = ????mm

Stock headgasket is 1.75mm when compressed and accomodates ???mm bore

Cylinder head

M30

Engine hardware

Use ARP head studs

Intake manifold

Use stock up to 400+hp

Exhaust manifold

Use Y-adapter between turbo flange and original twin manifolds
Custom log type manifold
Custom header style
Cast manifold TCD or cartech

Turbocharger

Use any suitable garrett with ~60mm compressor inducer and at least 0.86 AR T4 housing
At least Holset HX35 with anothing lower than 16cm^2, and up to 25cm^2

Fueling

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

Standalone engine management with at least 300cc/min injectors, and preferably 440cc or higher
Most stock BMW fuel pumps good for just over 250hp of fuel, but an inline Bosch or Walbro in conjunction with the stock pump is the safer option

Ignition

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

Use colder plugs. For most applications, a Bosch 5 or an NGK 7 are fine, usually gapped to 0.7-0.8mm. For higher boost, it might be safer to go with NGK 8's.
Proper gapping of the plugs is necessary if using the stock coil. Depends on plug type (copper/iridium etc) and boost levels. For wastespark conversions, a gap of 0.8mm can usually be used, otherwise 0.7mm should be fine.
Aftermarket ignition leads are usually a good thing as the stock ones normally tend to be old and tired. Magnecor KV85 are fine.