VW Mk.5 Golf GTi: EA113 AXX/BWA/BPY/CAWB engines

Introduction

The Volkswagen Mk.5 Golf GTi was powered by 2.0-litre turbocharged petrol engines that were members of Volkswagen’s EA113 engine family and had the codes AXX, BWA, BPY and CAWB. Key features of the Mk.5 Golf GTi’s 2.0 TFSI engine included its:

• Cast iron block;
• Aluminium alloy cylinder head;
• Double overhead camshafts;
• Four valves per cylinder with variable intake valve timing;
• BorgWarner K03 turbocharger;
• Intercooler;
• Variable intake manifold;
• Direct injection (Volkswagen’s ‘Fuel Stratified Injection’ or ‘FSI’);
• Compression ratio of 10.5:1; and,
• Mass of 152 kg.

For simplicity, this article will refer to the Volkswagen Mk.5 Golf GTi‘s AXX/BWA/BPY/CAWB engines as the ‘2.0 TFSI engine’.

Block

The 2.0 TFSI engine had a grey cast iron (CG25) block with 82.5 mm bores and a 92.8 mm stroke for a capacity of 1984 cc. Within the cylinders, the contact surfaces were honed by liquid blasting. Furthermore, the 2.0 TFSI engine had a die-forged steel crankshaft which operated on five main bearings.

To offset second degree inertial forces, the 2.0 TFSI engine had two chain driven counter-rotating balance shafts.

Crankcase breather system

The 2.0 TFSI engine had a crankcase breather system whereby blow-by gases from the crankcase were passed via the primary oil separator in the oil filter module to the cylinder head cover. When this occurred, the blow-by gases were mixed with those from the cylinder head and passed through a labyrinth where further oil separation occurred.

Cylinder head

The 2.0 TFSI engine had a cast aluminium alloy cylinder head with double overhead camshafts. While the intake camshaft was driven by a roller chain, the exhaust camshaft was belt-driven and had an elliptical toothed belt pulley on the crankshaft to reduce rotational vibrations on the camshaft and pulling forces on the toothed belt.

The 2.0 TFSI engine had four valves per cylinder that were actuated by roller finger cam followers with hydraulic valve clearance compensation. For heat dissipation, the exhaust valve stems were filled with sodium.

For the 2.0 TFSI engine, the intake camshaft provided variable intake valve timing and was continuously adjustable over a range of 42 degrees relative to the crankshaft.

BorgWarner K03 turbocharger

The 2.0 TFSI had a single water-cooled turbocharger that was integrated with the exhaust manifold into a single unit. For the AXX, BWA, BPY and CAWB engines which produced peak power of 147 kW, a BorgWarner K03 turbocharger provided peak boost pressure of 0.9 bar (13.05 psi). It is understood that the BorgWarner part number for the turbocharger is 5303-970-0105 (OEM part number 06F 145 701D/E/G).

The speed of the turbine, and hence charge pressure, was controlled by a charge pressure control solenoid valve and vacuum unit, with the latter actuating the wastegate valve via a linkage. When opened, the wastegate valve created a channel for exhaust gases to bypass the turbine.

To prevent the turbocharger from braking too heavily in overrun and between gear changes, an electric air recirculation valve was used. Ordinarily, pressure would accumulate in the compressor housing during overrun due to the prevailing charge pressure – this pressure build-up would cause the compressor wheel to brake heavily, leading to a reduction in the prevailing charge pressure (turbo drop). To prevent this from happening, the air recirculation valve was opened by an electric servo motor, creating a bypass channel for compressed air to flow from the compressor wheel back to the suction side of the compressor circuit, thereby keeping the turbine at a constant speed. When the throttle valve was opened, the turbocharger air recirculation valve would close and charge pressure was restored.

Fuel Stratified Injection (FSI)

The 2.0 TFSI engine had Volkswagen’s ‘Fuel Stratified Injection’ or ‘FSI’ which directed fuel directly into the combustion chamber (as opposed to port injection which injected fuel upstream of the chamber) at a pressure of up to 115 bar. The high-pressure fuel pump was driven by a four-fold cam on the exhaust camshaft.

Fuel was only injected in the piston’s compression phase (rather than the conventional induction phase) and was directed into the intake air stream as it moved towards the spark plug. The 2.0 TFSI engine had two injection modes:

• Dual injection for cold starts: a special mode for rapid heating of the catalytic converter, the primary injection occurred on the intake stroke at approximately 300 degrees before top dead centre (TDC) of ignition and the fuel distributed itself homogeneously. The second injection occurred at approximately 60 degrees before TDC in the compression phase. The richer mixture formed around the spark plug such that timing could be retarded and, since the exhaust valves were open during combustion, the hotter exhaust gases contributed to faster warm-up of the catalytic converter (around 30-40 seconds from start-up); and,
• Homogeneous injection: injection occurred in the area of the spark plugs with a stoichiometric air:fuel mixture (14.7:1)

Since the engine operated in homogeneous mode during normal running, tumble flaps were used to improve mixture formation. At low loads and engine speeds from 1000-5000rpm, the tumble flaps were closed to:

• Improve idle quality after cold starts;
• To increase the tumble effect and provide smoother running; and,
• To prevent engine jolts.

At other engine loads and speed ranges, the tumble flaps were open for free air flow and maximum performance.

Ignition

The 2.0 TFSI engine had four single spark ignition coils and cylinder-selective anti-knock control that was controlled by the Bosch Motronic MED 9.1 engine management system. Furthermore, the 2.0 TFSI engine had a compression ratio of 10.5:1.