What is a Wastegate? — Boost Control for Turbocharged Engines
What is a Wastegate?
A wastegate is a valve that controls how much exhaust gas reaches the turbocharger's turbine. By diverting exhaust around the turbine, the wastegate regulates boost pressure — preventing the turbo from spinning too fast and building too much boost. It's the primary boost control mechanism on every turbocharged engine.
Internal vs External Wastegates
| Type | Location | Best For |
|---|---|---|
| Internal | Built into the turbo housing | Factory turbos and mild upgrades — simple, compact, no extra plumbing |
| External | Separate unit on the exhaust manifold | High-power builds — larger port, more precise control, handles higher exhaust flow |
Why Wastegates Matter for Tuning
When you ECU tune a turbocharged engine, you're typically increasing the boost target — telling the ECU to keep the wastegate closed longer so the turbo builds more pressure. At Stage 1 and Stage 2, the factory internal wastegate handles the additional duty without issue. At Stage 3 with upgraded turbos, the exhaust flow can overwhelm the internal wastegate's ability to regulate boost, causing boost creep — uncontrolled boost rise that can damage the engine.
Wastegate Upgrades
An external wastegate upgrade solves boost creep on high-power builds. External wastegates have larger ports (typically 38mm-44mm vs the factory ~30mm), stiffer springs, and can dump exhaust directly to atmosphere (screamer pipe) or back into the exhaust system. On the AMG M177 platform, wastegate upgrades become relevant above ~800 HP — below that threshold, the factory internal wastegate is adequate when properly calibrated via ECU tuning.
Related
See our guides on turbo upgrades, downpipes, and intercooler upgrades for the complete turbo system picture.