Each cylinder has two intake valves and two exhaust valves, making the total for a four-cylinder power plant 16 and 24 for a six-cylinder. Previously a four-cylinder engine would have had an eight valve cylinder head and a six-cylinder a 12 valve head.

How it works:

  • Twin intake valves open during induction prior to compression stroke to deliver atomised fuel/air mix
  • Twin exhaust valves open to expel gases for exhaust stroke

Advantages:

  • Two intake and two exhaust valves improve the airflow both into and out of the engine.
  • Provides better mixing of the air and fuel, improving economy and lowering exhaust emission levels
  • 4-valve head design positions the injector in the center of the piston and combustion chamber for even piston loads and uniform spray pattern.
  • Having the injector in the centre means the piston bowl can be symetrical.
  • Traditional designs have offset injectors which means the piston bowl shape has to be varied to get a good fuel/air mix.
  • With a central injector it is easier to get a better and more consistent mix over the whole cylinder volume.

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