A
wastegate
is a valve that
diverts exhaust
gases away from the
turbine wheel in a
turbocharged engine
system. Diversion of
exhaust gases
regulates the
turbine speed, which
in turn regulates
the rotating speed
of the compressor.
The primary function
of the wastegate is
to regulate the
maximum boost
pressure in
turbocharger
systems, to protect
the engine and the
turbocharger.
Wastegate sizing is invsersely proportionate to the desired level of boost and is somewhat agnostic to the size or power of the engine. One vendor's guide for wastegate sizing is as follows:
-
big turbo/low boost = bigger wastegate
-
big turbo/high boost = smaller wastegate
-
small turbo/high boost = smaller wastegate
-
small turbo/low boost = bigger wastegate
Wastegate types: External wastegate and Atmospheric/divorced wastegates
An external
wastegate
Is a separate self-contained
mechanism typically used with
turbochargers that do not have
internal wastegates. An external
wastegate requires a specially
constructed turbo manifold with a
dedicated runner going to the
wastegate. The external wastegate
may be part of the exhaust housing
itself. External wastegates are
commonly used for regulating boost
levels more precisely than internal
wastegates in high power
applications, where high boost
levels can be achieved. External
wastegates can be much larger since
there is no constraint of
integrating the valve or spring into
the turbocharger and turbine
housing. It is possible to use an
external wastegate with an
internally gated turbocharger. This
can be achieved through a specially
designed bracket that easily bolts
on and restricts the movement of the
actuator arm, keeping it from
opening. Another route involves
welding the internal wastegate shut
which permanently keeps it from
opening, but failure of the weld can
allow it to open again.
Atmospheric/divorced
wastegates
A "divorced"
wastegate dumps the
gases directly into
the atmosphere,
instead of returning
them with the rest
of an engine's
exhaust. This is
done to prevent
turbulence to the
exhaust flow and
reduce total back
pressure in the
exhaust system.
Divorced wastegate
dumper pipes are
commonly referred to
as "screamer pipes"
due to the unmuffled
waste exhaust gases
and the associated
loud noises they
produce.
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