Wastegates provide a means to control the boost pressure of the
turbo charged engine. Wastegates work to bypass exhaust flow from
the turbine wheel. Bypassing the exhaust flow reduces the power
driving the turbine wheel to match the power required for a given
boost level. Similar to the BOV, the Wastegates uses boost
pressure and spring force to regulate the flow bypassing the
turbine.

Wastegates are bolted to exhaust manifold or header. The
advantage of external Wastegates is that the bypassed flow can be
reintroduced into the exhaust stream further downstream of the
turbine. This tends to improve the turbine's performance.