VR6 Engine - Detailed Specifications

Detailed Specifications

The original VR6 engine features a one-piece grey cast iron crankcase and cylinder block, and one lightweight aluminium alloy crossflow cylinder head, with two valves per cylinder, operated by chain-driven overhead camshafts. All fuel and ignition requirements of the VR6 engine are controlled by Bosch Motronic engine control unit (ECU). This engine management system features a Mass flow sensor, dual knock sensors for cylinder-selective ignition knock regulation, and Lambda regulation for the air/fuel mixture. Exhaust gases are channeled through a three-way catalytic converter.

Volkswagen Group identifies the original VR6 by the chassis "AAA" engine ID code. It operates on the four-stroke cycle, has an engine displacement of 2.8 litres. The 2.8 VR6 cylinder bore diameter is 81.0 millimetres (3.19 in), and the piston stroke is 90.0 millimetres (3.54 in), although some European engines had a displacement of 2.9 litres (this variant identified by the "ABV" engine ID code). The 2.9 VR6 cylinder bore diameter is 82.0 millimetres (3.23 in), and the piston stroke is 90.0 millimetres (3.54 in). The "Vee" angle is 15°, and the compression ratio (CR) is 10:1.

The drop-forged steel, six-throw crankshaft runs in seven main bearings. The connecting rod bearing journals are offset 22° to one another. Two overhead camshafts (OHCs) operate the automatic hydraulic valve lifters which, in turn, open and close the 39.0 millimetres (1.54 in) intake valves and 34.3 millimetres (1.35 in) exhaust valves. Since the two 'rows' of pistons and cylinders share a single cylinder head and head gasket, the piston crown (or top surface) is tilted. Intake and exhaust valves need different camshafts to vary valve overlap (they may be coaxial like in some 90° V8). To minimize the number of camshafts, both rows share their camshafts (similar some 90° V8s). The intake and exhaust ports pass closely within the cylinder head; this then heats the intake air/fuel mixture before it is ignited by the spark plug, which limits the amount of timing advance that can be used due to an increased possibility of pre-detonation of the air/fuel mixture and has the effect of reducing power. This also cools the exhaust gasses, which hampers the operation of the catalytic converter.

Because of the cylinder arrangement in the VR6 - with two rows of combustion chambers within the same cylinder head, the intake and exhaust ports between the two rows of cylinders are of varying lengths. Without compensation, these varying port lengths would result in the two rows of cylinders producing different amounts of power at a particular engine RPM. Depending on the specific generation of VR6, the difference in port lengths are compensated for by specific tuning of the intake manifold, the camshaft overlap and lift profile, or a combination thereof. In the original VR6, exhaust gases are channeled from two 3-branch cast iron exhaust manifolds (one dedicated to three cylinders) into a sheathed Y-pipe. From there, they are channeled into a single flow pipe, before passing over the heated oxygen sensor, and then to the catalytic converter.

The fuel injectors, operated by the Bosch Motronic engine control unit (ECU) system, are mounted behind the bend of the intake manifolds. The water pump housing is cast integral with the cylinder block. VR6 engines also use an additional auxiliary electric pump to circulate the engine coolant whilst the engine is running, and also during the cooling fan 'after-run' cycle, in addition to the belt-driven main water pump.

A replaceable oil filter cartridge element is used on the VR6 engine. The sump-mounted oil pump is driven via an intermediate shaft. An oil pressure control valve is integrated in the pump.

The one-piece cylinder block and crankcase is made from pearlitic grey cast iron with microalloyed steel (microalloy). The two rows of three cylinders are arranged at a 15° axial angle from the crankshaft. The cylinder bores are 81.0 millimetres (3.19 in) in diameter, with a spacing of 65 millimetres (2.6 in) between cylinders. They are staggered, but overlap along the length of the engine block - to allow the engine to be shorter and more compact than conventional V6 engines.

The centerline of the cylinders are also offset from the centerline of the crankshaft by 12.5 millimetres (0.49 in). To accommodate the offset cylinder placement and narrow "Vee" design, the connecting rod bearing journals are offset 22° to each other. This also allows the use of a 120° firing interval between cylinders. The firing order is: 1, 5, 3, 6, 2, 4.