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Wastegate

Car culture term

Wastegate
Photo: Panoha / Wikimedia Commons · CC BY-SA 3.0

What is Wastegate?

A valve that diverts exhaust gas around the turbocharger turbine to control boost pressure. Internal (factory) or external (aftermarket race) variants.

Wastegate is a valve that diverts exhaust gas away from the turbocharger turbine to control maximum boost pressure. Without a wastegate, the turbocharger would continue to spool faster as exhaust flow increased, eventually producing excessive boost that could damage the engine. The wastegate opens when target boost is reached, bypassing exhaust around the turbine wheel and limiting further turbo speed increase.

Two main types exist. Internal wastegates are integrated into the turbocharger housing, with a flap valve that opens to vent exhaust around the turbine. External wastegates are separate units mounted upstream of the turbo, often vented through a dedicated exhaust pipe (which produces a distinctive screaming sound). External wastegates are common in serious aftermarket turbo applications because they offer larger valve sizes for high-flow applications.

The screaming sound of an external wastegate venting to atmosphere is a hallmark of competition turbocharged cars (drag racing, drift, time attack). The sound is the result of high-pressure exhaust flowing through the small wastegate orifice. Some street cars use external wastegates with the dump tube routed back into the main exhaust to reduce noise; race cars typically vent directly to atmosphere.

Related terms

TurboBOVIntercooler

Frequently asked questions

What is the difference between internal and external wastegates?
Internal wastegates are built into the turbo housing with a small flap valve. External wastegates are separate units mounted on the exhaust manifold or downpipe, typically with much larger valve sizes. Internal wastegates are common in factory applications. External wastegates are typical in aftermarket high-flow turbo builds.
Why do some wastegates scream?
External wastegates that vent directly to atmosphere produce a high-pitched scream as exhaust gas exits the wastegate orifice at high pressure. The sound is associated with race-tuned cars. Some street builds route the wastegate dump tube back into the main exhaust to reduce noise but lose the distinctive sound.
How does a wastegate know when to open?
Most wastegates are spring-loaded with a pneumatic actuator that uses intake manifold pressure to push against the spring. When manifold pressure exceeds the spring rate, the wastegate opens. Modern engine management can also control wastegates electronically through boost control solenoids that vary the pressure signal.
Can a wastegate fail?
Yes. Wastegate flapper failures can cause uncontrolled boost (overboost), turbo damage, or engine damage. Wastegate actuator failures can cause inability to reach target boost. Stuck wastegates are a common cause of boost-related driveability issues. Inspection during turbo service is standard.
Do all turbocharged cars have wastegates?
Essentially all production turbo cars have wastegates. Without one, boost would be uncontrolled and would damage the engine quickly. Some advanced production designs use variable geometry turbochargers (VGTs) that control boost through turbine vane position rather than wastegate, but most production cars still use wastegates.
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