Wastegate Buyer's Guide
A wastegate is a pressure relief valve that regulates maximum boost pressure by routing exhaust gas around the turbocharger's turbine. When the wastegate is closed, all exhaust gas spins the turbine, building boost on the intake side. When target boost pressure is reached, the wastegate opens allowing exhaust gases to bypass the turbine, slowing the turbocharger and controlling boost pressure. Ultimately, your wastegate sets your maximum boost pressure. A wastegate is a critical component to protect both your engine and turbocharger from damaging overboost. This guide walks you through how wastegates work, the difference between internal and external wastegates, and how to choose the right one for your build.
How Wastegates Work
All wastegates operate on the same core principle: intake manifold pressure acts on one side of a diaphragm, and a spring pushes back on the other. When boost pressure rises high enough to overcome the spring, the diaphragm flexes and opens the valve, letting exhaust gas bypass the turbine. The strength of the spring determines how much boost it takes to open the valve, and therefore sets your maximum boost pressure.
The two types of wastegate, internal and external, differ in where this mechanism lives and how much exhaust gas they can flow.
Internal Wastegates
An internal wastegate is built into the turbocharger itself. A flap door within the turbine housing opens when boost gets too high, controlled by the spring-and-diaphragm mechanism described above. When boost overcomes the spring, an actuator arm pushes the flap open, allowing exhaust gas to bypass the turbine.
Internal wastegates are sized for factory boost and power levels. When you modify your engine to produce more power than stock, the internal wastegate's relatively small flap may not be able to bypass enough exhaust gas to keep boost under control. This leads to a problem called boost creep, where the wastegate can't divert enough gas to slow the turbine, causing boost to climb uncontrollably at high RPM. Boost creep can cause engine knock and potentially catastrophic engine damage.
External Wastegates
To solve this issue, an external wastegate can be used. An external wastegate is a separate component plumbed into the exhaust manifold, ahead of the turbocharger. Because it isn't constrained by the turbo housing, it can be sized to match your specific power level and turbo setup. External wastegates use the same spring-and-diaphragm operating principle as internal units.
External wastegate springs can be swapped out to adjust maximum boost pressure. A stiffer spring raises max boost; a softer spring lowers it. You can add further control with a boost controller. Read more in our Boost Controller Buyer's Guide.
The best way to choose a spring rate is to consult your tuner and follow their recommendation. If you swap a wastegate spring yourself, look up the correct procedure first, these springs are under significant pressure and can cause injury if released improperly.
External Wastegate Plumbing
External wastegates are plumbed before the turbocharger somewhere on the exhaust manifold. It is recommended that they are placed at a 45 degree angle to the piping with a smooth transition to ensure maximum flow. A wastegate placed at a 90 degree angle flows 50% less, making the angle/placement critical.
Exhaust gas bypassed by the wastegate should be routed back into the exhaust system, ideally at a 45-degree angle at least 18 inches downstream of the turbo to minimize backpressure and turbulence. Exhaust gases can also be vented to atmosphere, although this is not recommended due to the increased emissions and noise. When vented to the atmosphere, the pipes attached to the wastegate are often called screamer pipes due to their excessive noise.
Sizing Your Wastegate
Proper wastegate sizing depends on three factors: your turbocharger size, your intended boost pressure, and your engine displacement.
The key concept to understand is that a wastegate doesn't need to flow all of your exhaust gas, only the portion that must bypass the turbine to hold your target boost. The more exhaust gas you need to divert, the larger the wastegate required.
Consider a large turbo, which naturally wants to produce high boost. If you want to run that big turbo at a lower boost pressure, you have to bypass more exhaust gas to hold it down, which requires a larger wastegate. The general recommendations based on turbo size and intended boost pressure are:
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Big Turbo / Low Boost = Larger Wastegate
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Big Turbo / High Boost = Smaller Wastegate
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Small Turbo / High Boost = Smaller Wastegate
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Small Turbo / Low Boost = Larger Wastegate
The last thing that needs to be considered is your engine displacement. Larger engines produce more exhaust gas and therefore need more wastegate capacity. A very large engine may require multiple external wastegates to bypass enough gas to avoid boost creep. Twin scroll turbos also require two wastegates, one for each scroll.
As a general starting point, a 44mm wastegate suits most moderate applications. There's no real performance downside to a larger wastegate beyond cost, so when in doubt, size up.
Electronic Wastegates
Electronic wastegates open and close the valve electronically rather than relying on a spring and boost pressure. This eliminates the need to swap springs or run a separate boost controller, since boost is managed electronically. Electronic wastegates are expensive but can be the right choice for a high-performance build where precise, dynamic boost control is a priority.
Conclusion
The right wastegate depends on your power goals and turbo setup. For stock or mildly modified builds, an internal wastegate is often sufficient. Once you push beyond factory power levels, an external wastegate provides the flow capacity and adjustability needed to keep boost under control and avoid boost creep. Size your wastegate based on your turbo, target boost, and engine displacement, and pay close attention to inlet angle, as poor placement can cripple flow. Set your maximum boost by selecting the correct spring, and consult your tuner for specific recommendations. Get these details right and you'll make reliable boost while protecting your engine and turbocharger. You can find all the parts you need and plan your build on RideBuilder.
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