VR5 engine

The VR5 engines are a family of petroleum fuelled Internal combustion engines developed by the Volkswagen Group and produced from 1997 to 2006. They are derived from the VR6 engine family, also developed by Volkswagen, but with one fewer cylinders. The VR5 is highly compact, thanks to the narrower angle of 15° and a displacement of 2324 cc. The VR5 was the first production block to use five cylinders in a VR design with a 15-degree angle.

Technical Information
A VR5 engine block houses two staggered rows of cylinders within a single, short and wide bank – one row of two cylinders and the other having three. This narrow-angle, single bank block makes the five cylinder engine as short as an inline three cylinder, while also having single inlet and exhaust manifolds. In a transverse layout the three-cylinder row is located towards the front, and in a longitudinal layout towards the right. Due to the narrow bank-angle of the two cylinder rows, the arrangement works as a zig-zag staggered, W-patterned inline five-cylinder. The engines have a firing order of 1-2-4-5-3.

The VR5 was initially made with 2 valves per cylinder as the AGZ engine from 1997 until 2000, resulting in a 10 valve engine producing 148 HP at 6000 RPM and 209 Nm of torque at 3200 RPM. The engine was updated in 2000 as the AQN/AZX engine adding an additional 2 valves per cylinder and variable valve timing, resulting in an 20 valve engine now with 4 valves per cylinder, producing 168 HP at 6200 RPM and 162 lb.ft 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 81.0 x bore x stroke, resulting in 464.8 cc 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. The VR5 was used in the Volkswagen Golf, Bora, New Beetle and Passat. The engine was also included in the Toledo, a saloon car made by Volkswagen Group's subsidiary SEAT.