A VR5 engine block houses two staggered rows of
cylinders within a single, short and wide bank – one row of two cylinders and one row of three. This narrow-angle, single-bank block makes the five cylinder engine as short as an inline three cylinder, while also having only one
inlet and
exhaust manifold. In a
transverse layout, the three-cylinder row faces towards the front; in a
longitudinal layout, it faces towards the right. The cylinders have a firing order of 1-2-4-5-3. The VR5 was initially made with two valves per cylinder as the AGZ engine from 1997 until 2000, resulting in a 10 valve engine producing at 6000 RPM and of torque at 3200 RPM. The engine was updated in 2000 as the AQN/AZX engine, with four valves per cylinder and variable valve timing, producing at 6200 RPM and at 3300 RPM. Both versions of the engine had cast aluminium alloy
cylinder heads and cast iron
cylinder blocks.
Valvetrain and cylinder head The AGZ had 10 valves in total with 2 unequal sized valves per cylinder and chain driven
camshafts. When this was updated the AQN/AZX engine had 20 valves in total, with 4 unequal sized valves per cylinder. Due to the use of a single
cylinder head, a key design principle of the VR engines, exhaust and intake ports were of unequal length between the two cylinder banks. To mitigate this, Volkswagen used unequally sized valves to ensure even flow and power output from the cylinders.
Engine block and pistons The AGZ engine used a cast iron cylinder block with five staggered cylinders. Each cylinder was bore x stroke, resulting in per cylinder with a 0.90:1
stroke ratio creating an
undersquare/long stroke engine. The top of each
piston was angled to accommodate for the use of the 15° narrow V angle.
Aspiration, fuel system, and engine management The AGZ engine was managed by a
Bosch Motronic M3.8.3
engine management system and the AQN/AZX engine by a Bosch Motronic ME7.1 engine management system. The engine used multi-point
common rail sequential
fuel injection, with fuel injected indirectly into the lower
inlet manifold section just before the cylinder head intake ports. Fuel and air delivery was controlled by a cable operated
throttle body, with a potentiometer monitoring throttle position and allowing the Motronic ECU to deliver the correct amount of fuel. The engine also had a vacuum actuated
variable intake manifold, controlled by the ECU via a valve part of the engines vacuum system. The valve is opened and closed depending on engine load, engine speed and throttle position. This allows the engine to take advantage of pressure waves created by the intake valves opening and closing. ==Applications==