In modern turbo engines the boost is controlled by a wastegate. This
can be either an integral wastegate that is part of the turbocharger (usually
the case in factory turbo applications), or an external one. When boost
is applied to a diaphragm in the wastegate actuator, it will open a valve
exhaust go past the turbine wheel. One can raise the boost from
stock setting by:
bleeding off part of the boost signal coming to the wastegate so that the
pressure at the diaphragm is less than actual manifold pressure. This can
be done by a simple bleeder valve or an electronically controlled one...
some are more accurate than others. Disconnecting the wastegate hose completely
is not recommended.
preloading the spring against which the diaphragm acts. This can be done
by either shortening the rod (some Garrett T3:s have a threaded rod making
adjustment very easy), adding shims under the bolts holding the actuator
or by bending the rod (crude but will do the same job).Note that this method
works only with integral wastegates, external ones don't have an actuating