Turbocharging a VW VR6 motor

Turbocharging a VW VR6 engine

This page describes the various paths that can be followed in the process of turbocharging a VW VR6 motor, from mild to wild. The information is arranged thematically, with no guarantee of its accuracy.

Engine block

The VR6 motor comes in a limited number of flavours:

2.9 litres, 90.3mm stroke, 82.0mm bore, engine code ABV (12 valves)
2.8 litres, 90.3mm stroke, 81.0mm bore, engine code AAA (12 valves)
3.2 litres, 95.9mm stroke, 84.0mm bore, engine code BJS (24 valves)
All crankshafts come with 60-2 trigger wheels fitted
Connecting rod dimensions for AAA/ABV:

C-C length: 164mm
Big end bore: 56.8mm
Big end width: 19.9mm
Pin diameter: 20mm
Small end width: 19.9mm

Since the VR6 was initial destined to be a diesel motor, the stock internals are strong and have been proven to be reliable at high output levels, especially if detonation is avoided. Various options to use for the bottom end are:

Stock rods and pistons, which usually yields a volumetric compression of around 10
Stock rods and pistons, with metal spacer, will lower the compression to 8.5 or 9 depending on thickness
R32 crankshaft can be fitted in 12V block will provide a stroked motor, but will require customs pistons
Aftermarket forged steel rods, with forged aluminum pistons. Bore size up to 84mm possible if the block is crack-free, but for turbo avoid more than 83mm bore.

Cylinder head

The 12V head can be made to flow well with extensive reworking, but stock for stock the 24V head is better. Possible additions:

Stiffer valve springs to allow higher rpm safely and to overcome the newfound positive manifold pressure
Titanium retainers are half the weight of stock steel retainers (~20g each) to allow higher rpm safely

Engine hardware

Use stock VW metal headgasket (p/n 050 103 383 A) for bores up to 83mm
Use ARP head studs (p/n ARP-204-4705 for 12V) to help avoid blown head gaskets
Raceware headstuds for 24V models
Use ARP rod bolts (p/n ARP-204-6006) to help keep the rods INSIDE the cylinder block.

Intake manifold

Either stock or custom:

Use stock manifold (plastic on 24V models)
Custom short intake manifold helps shorten intercoole piping among other benefits.

Exhaust manifold

Two options:

Use cast log-type manifold
Use stock VR6 manifolds in conjunction with y-pipe to connect the manifolds to a turbo flange

Turbocharger

Use anything suitable for a 2.8-3.2 litre motor running a maximum RPM of 7000. The choices are many:

For good low-rpm response and reasonable power, a T58 with O-trim wheel and 0.58AR housing
The next stage up would be a T61 with P-trim turbine wheel and 0.70AR wheel
Holset HX40 or HX35 with anything from 12-16cm housing will work well too

Fueling

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

Remapping stock ECU, using bigger MAF, and bigger (440cc) injectors
Standalone engine management with at least 300cc/min injectors, and preferably 440cc or higher
Most stock VW 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 VR6 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.
Aftermarket ignition leads are usually a good thing as the stock ones normally tend to be old and tired. Magnecor KV85 are fine.