Waste Gate

  A Waste Gate or Wastegate is a device that is mounted to a turbocharger and limits the maximum amount of boost and pressure of that turbo.
  Limiting the maximum boost a turbo can develop is necessary especially in larger turbos as they can produce too much boost and damage the turbo and engine.
  Reason being the turbine in a turbo can rotate at multiple times the rpm of the engine once it spools up and develop tremendous amounts of boost.
  Any (small or large) supercharger by comparison can only rotate at a speed in relation to the rpm of the engine and their maximum boost can be easily determined.
  How the waste gate works is by allowing some of the exhaust gases to bypass the turbine wheel when the pressure of the gasses is high.
  The waste gate is a butterfly valve connected to the exhaust manifold before the turbo and a rod, spring and valve which is connected to the intake manifold after the turbo.
  Both valves remain closed by default via the spring which is attached to the valve intake and designed to be compressed under pre-set boost levels.
  If the incoming air has too much pressure it pushes and compresses the spring which pushes the rod and causes the butterfly valve to open and allow some of the exhaust gases to bypass the turbine which re-enters the exhaust lines directly after the turbine.
  Once the boost/pressure are at a controllable level where it can't compress the spring, the spring returns to normal and closes both valves.
  The wastegate must be designed to overcome certain challenges such as ensuring that only intake manifold pressure can open the valve and not exhaust manifold pressure.
  Both manifolds have valves and high levels of pressure in them so it is possible for pressure from the exhaust gases to force the valve open before the boost get high enough in the intake manifold.
  There are two types of wastegates, the internal and the external. This explanation has mostly been about the internal as most high end turbocharged vehicles will have internal wastegates.
  Internal wastegates are built into the turbine housing of the turbo and works well with most stock applications.
  External wastegates are usually added unto the exhaust manifold before the turbo and on the exhaust lines or headers after the turbo and is usually the choice for engines that produce very high boost.
  These are usually purchased as an aftermarket part and there are persons that replace their internal with an external for better boost control.
  External wastegates easily handle higher boost levels and the gasses that bypasses the turbine re-enters the exhaust line further down from the turbine so it puts less back pressure on the turbine and improves performance.
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