Turbo boost controls

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 that lets
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 rod.
• using a stiffer spring