Quote Originally Posted by Dieseldude View Post
Most turbos have blow-off valves, either for gas or diesels. These are normally referred to as wastegates. Boost pressure is plumbed through a pilot line to the wastegate actuator. At a predtermined boost pressure, the actuator pushes a valve to dump exhaust gasses to the exhaust pipe, and bypass the turbine wheel. This limits turbo rpm and boost pressure, providing safe operation to the turbo, as well as the engine.
eerrr... wastegate and blow-off valve are not the same...

Quote Originally Posted by Team-Integra.Net

Wastegate
Most turbos for street use will have an integrated wastegate, an internal wastegate. This is the simplest wastegate to use, from an installation standpoint, since it is already attached to the turbo and requires a minimum of vacuum hoses to work. The drawback of the internal wastegate is that on occassion, it will not flow enough exhaust gas for "perfect" boost control. Higher-flow wastegates are available, the external wastegate. These allow for more precise boost control as well as flow capabilities for very high powered engines, with a drawback of more moving parts and more complex vacuum configuration.

Blowoff Valve
An object in motion tends to stay in motion. That's the key principle behind having a blowoff valve in your turbo system. While not exactly necessary for a turbo system to work, a blowoff valve will help turbo boost response between shifts. For very high-powered vehicles, one blowoff valve may not be enough to vent excessive boost when the throttle is closed; in this case, it's perfectly acceptable to use several blowoff valves.