VW Mk.7 Golf GTi: CHHA/CHHB (EA888 Gen 3) Engine

Introduction

The VW Mk.7 Golf GTi and GTi Performance were powered by Volkswagen’s CHHB and CHHA engines, respectively; these 2.0-litre turbocharged petrol engines were members of Volkswagen’s EA888 Gen 3 engine family. Compared to the CCZB engine in the Mk.6 Golf GTi, key changes for the CCHB and CCHA engines included:

• Thinner cylinder walls;
• A lighter crankshaft;
• A new turbocharger supplied by IHI which provides peak boost pressure around 1.3 bar (compared to the BorgWarner K03 turbocharger in the CCZB engine which provided charge pressure of 1.0 bar);
• Variable intake and exhaust valve timing (previously intake only);
• Two-stage exhaust valve lift;
• A fully-electronic coolant control system;
• Direct injection and multi-point port injection (previously direct injection only);
• Introduction of a ‘Start/Stop’ function which enabled the engine to shut down when the vehicle was stationary in traffic;
• Additional mass reduction measures such as lightweight polymers for the oil pan and aluminium for various screws and fasteners.

Block

The EA888 Gen 3 engine had a closed-deck, grey cast iron (GJL 250) block with 82.5 mm bores and a 92.8 mm stroke for a capacity of 1984 cc. For the EA888 Gen 3 engine,

• The casting process was changed from conventional flat pouring to upright pouring; and,
• Nominal cylinder wall thickness was reduced from 3.5 +/- 0.8 mm to 3.0 +/- 0.5 mm.

Within the cylinder block, the EA888 Gen 3 engine had two balance shafts to counteract second degree inertial forces. The horizontally-staggered balance shafts rotated at twice the engine speed in opposite directions from one another, with the direction of the second shaft reversed by an idler gear. The balance shafts were made from spheroidal graphite cast iron and, for the EA888 Gen 3 engine, lower-friction roller bearings were introduced.

Crankshaft, connecting rods and pistons

The EA888 Gen 3 engine had a forged steel crankshaft that was induction hardened and operated on five main bearings. Whereas the crankshaft for the CCZB engine in the Mk.6 Golf GTi had eight counterweights, the lighter crankshaft for the CHHA/CHHB engines had four counterweights. Furthermore, the main bearing diameters of the crankshaft were reduced from 52 mm to 48 mm.

Like the CCZB engine, it is understood that the connecting rods for the CHHA/CHHB engines were made from 36MnVS4 and were cracked for precision fitting and reduce movement of the bearing cap under load.

For the EA888 Gen 3 engine, a new ‘strength-enhanced alloy’ piston coating was applied. Furthermore, an electric system was introduced to control the oil-jet cooling for the pistons.

Cylinder head

The EA888 Gen 3 engine is understood to have a cross-flow cylinder head that was made of AlSi10Mg and mounted on a three-layer metal head gasket. In a new development, however, the exhaust manifold for the EA888 Gen 3 engine was integrated into the cylinder head. Furthermore, the cylinder head had a fully integrated water-cooled exhaust gas circulation loop so that full load enrichment (i.e. enriching the fuel/air mix at higher loads) was no longer required for cooling, thereby improving fuel consumption at high loads.

Camshafts and valves

The EA888 Gen 3 engine had hydro-formed, double overhead camshafts that were driven by gear chains (as opposed to roller chains). For the EA888 Gen 3 engine, the intake and exhaust valves were actuated by roller cam followers with needle bearings and hydraulic valve clearance adjusters. It is understood that both the intake and exhaust valves were chrome-plated and had reinforced seats. While the intake valves had solid stems, the exhaust valves were also tempered and had sodium-filled stems for heat dissipation.

Variable valve timing and exhaust valve lift

The EA888 Gen 3 engine had variable intake and exhaust valve timing as well as variable exhaust valve for better control of the charge exchange process.
The variable exhaust valve lift system is understood to be based on the ‘Audi Valve Lift System’ (AVS) whereby the camshaft had two valve lift contours for each exhaust valve (small and large). In this system, change-over between the cam lobe contours was achieved by the longitudinal displacement of the cam elements via electromagnetic solenoid-type actuators. One actuator moved the cam element on the camshaft for large valve lift, while the other actuator reset the cam element for small valve lift.

At low engine speeds (up to around 3100 rpm), the small profile cam lobe contour was used to:

• Provide late exhaust valve opening;
• Prevent the back-flow of exhaust gas during the valve overlap phase; and,
• Enable advanced intake valve timing.

Specifically, the positive cylinder pressure gradient allowed the combustion chamber to be effectively purged – this enhanced fuel/air mixture formation by reducing the residual gas content in the cylinder and enabled advanced intake valve timing since less intake air was expelled after BDC (bottom dead centre). As a result, greater torque was produced at low engine speeds and charge pressure could be accumulated faster.

At high engine speeds, the large profile cam lobe contour was used.

IHI turbocharger

The CHHB/CHHA engines have an IHI turbocharger that is integrated with the exhaust manifold which provides peak boost pressure of 1.3 bar (18.9 psi). Compared to the BorgWarner K03 turbocharger for the Volkswagen Mk.6 Golf GTi‘s CCZB EA888 engine, changes for the IHI turbocharger in the CHHB/CHHA engines include:

• A new alloy for the turbine wheel that can withstand exhaust gas temperatures up to 980 degrees Celsius;
• A new electric wastegate actuator that reduces boost pressure when the power is not needed to reduce fuel consumption;
• The fitment of pulsation damper; and,
• The addition of an oxygen sensor mounted directly upstream of the turbine wheel;

Cooling

The EA888 Gen 3 engine introduced a fully-electronic coolant control system for more efficient thermal management. The system included a new type of rotary vane module that could block coolant entry into the engine or adjust to low volumetric flows in the engine’s warm-up phase. As a result, shorter warm-up times were achieved, thereby reducing frictional losses and improving fuel economy. At higher engine temperatures, coolant temperature could be adjusted quickly and variably as a function of engine load and external constraints.

Port and direct injection

The EA888 Gen 3 engine has both direct and port fuel injection via separate sets of injectors. The EA888 Gen 3 engine adopted a dual injection system to reduce particulate emissions and comply with Euro 6 emissions standards. The direct injection system used six-hole injectors that provided fuel pressure up to 200 bar.

Based on inputs from sensors, the engine management system controlled the injection volume and timing of each type of fuel injector, according to engine load and engine speed, to optimise the fuel:air mixture for engine conditions. The injection system is understood to have the following operating conditions:

• Cold start: the port injectors provided a homogeneous air:fuel mixture in the combustion chamber, though the mixture around the spark plugs was stratified by compression stroke injection from the direct injectors. Furthermore, ignition timing was retarded to raise exhaust gas temperatures so that the catalytic converter could reach operating temperature more quickly;
• Low engine speeds: port injection and direct injection for a homogenous air:fuel mixture to stabilise combustion, improve fuel efficiency and reduce emissions; and,
• Medium to high engine speeds and loads: direct injection only to utilise the cooling effect of the fuel evaporating as it entered the combustion chamber to increase intake air volume and charging efficiency.

Ignition

The CHHA/CHHB engines had four single spark ignition coils and cylinder-selective anti-knock control. Furthermore, the CHHA/CHHB engines had a 1-3-4-2 firing order and compression ratio of 9.6:1.