Most Subaru WRX and Subaru STI builds run internal wastegates from the factory. The stock turbo manages boost pressure through an integrated valve inside the turbine housing, which works adequately at factory power levels. However, as builds push into bigger turbos and higher boost targets, the internal wastegate becomes a limiting factor. It cannot flow enough exhaust gas to control boost precisely, which leads to boost creep, inconsistent power delivery, and tuning instability. The Turbosmart 40mm CompGate40 External Wastegate addresses this directly, providing a dedicated external valve that removes boost control from the turbo housing entirely and gives the tuner precise, stable control over boost pressure.
This post covers what an external wastegate does, when a WRX or STI build actually needs one, and what the Turbosmart CompGate40 provides specifically.
What an External Wastegate Actually Does
A wastegate controls boost pressure by regulating how much exhaust gas reaches the turbocharger’s turbine wheel. When boost reaches the target level, the wastegate opens and diverts exhaust flow away from the turbine, which slows turbo speed and prevents boost from climbing further. The target pressure at which the wastegate opens is determined by the spring inside the wastegate housing, modified by boost controller solenoid signal.
An internal wastegate integrates this valve directly into the turbine housing. The compact design works well for OEM applications where packaging, cost, and simplicity are priorities. However, the internal valve’s small size limits how much exhaust it can divert at once. On a large-frame turbo pushing high boost, the internal wastegate cannot open wide enough or flow enough gas to keep boost stable, which causes boost to continue climbing past the target. This is boost creep, and it is the primary reason high-power builds switch to an external wastegate.
An external wastegate mounts separately from the turbo, typically on a dedicated port in the exhaust manifold or turbo outlet. Because it is a standalone valve with its own housing and can be sized appropriately for the application, it flows significantly more exhaust gas than an internal gate. The result is precise, stable boost control that holds the target pressure consistently across the RPM range. For a WRX or STI owner chasing 500 horsepower and above, the external wastegate is what makes the difference between a tune that holds boost and one that spikes or creeps unpredictably.
What the Turbosmart CompGate40 Provides
The Turbosmart GenV WG40 CompGate40 is the largest wastegate in Turbosmart’s GenV range and the highest flowing 40mm wastegate in the lineup. The GenV design was a ground-up rework of the previous generation, with CFD optimization validated in-house for maximum flow and thermal management. The only carried-over feature from the Gen4 range was the mounting orientation, ensuring compatibility for builders upgrading from older Turbosmart hardware.
Key design features include a collar-locking system that secures the actuator cap without tools, a variable actuator cap and base that allows 360-degree positioning of reference hose routing, and strap-type V-band clamps for a secure, leak-free seal at the flange. An optional liquid cooling provision allows coolant lines to be routed through the wastegate body on extreme heat applications. Reference ports use 1/8-inch NPT fittings, and the full range of available springs ships with the unit.
This unit is available in four colors: Blue, Black, Purple, and Red, all at the same price point. The 14 PSI spring that comes installed sets the base boost pressure at which the gate opens without boost controller signal. For builds running a boost controller solenoid, that base pressure is modified electronically to allow higher targets while the spring provides the failsafe floor. The 7 PSI version is also available for builds that need a lower base pressure, typically lower boost street builds or setups where the boost controller has a wider adjustment range.
When a WRX or STI Build Needs an External Wastegate
Not every modified WRX or STI needs an external wastegate. For builds running the stock turbo, a mild upgrade, or moderate boost increases on a factory-style turbo manifold, the internal wastegate manages boost adequately. The external wastegate conversation starts when one or more of the following conditions applies to the specific build.
Boost creep is the clearest signal. If the tune shows boost continuing to climb past the target in the upper RPM range rather than holding flat, the internal wastegate is not keeping up. This is common on big-frame turbo setups where exhaust energy at high RPM overwhelms the internal gate’s flow capacity. The customer review on this product says it plainly: “Switched my tial 38mm to this and boost creep issues went away immediately.”
Large-frame turbo installations are the second driver. Builds running turbos in the TD06SL2 54X class or larger generate more exhaust energy than factory-scale hardware, and a properly sized external wastegate is part of what makes those builds tune correctly. The post on supporting mods required for big turbo WRX builds covers where the wastegate fits in the full supporting mods list for builds at this level.
Competition and track builds are the third scenario. Where consistent boost is critical lap to lap, an external wastegate removes the variability that internal gates introduce under sustained high load. For STI owners building toward serious competition use, the STI engine build and power goals hub covers how boost control fits into a high-power STI build sequence. WRX owners can find the equivalent context at the WRX turbo airflow upgrades hub.
External Wastegate vs Internal Wastegate: What Changes in Practice
Switching from an internal to an external wastegate requires a turbo manifold or exhaust manifold with a dedicated wastegate port and a separate dump tube to route the vented exhaust gases. This means the external wastegate conversion is a fabrication and planning exercise, not a bolt-on swap. The turbo manifold, the wastegate position, and the dump tube routing all need to be designed as a system before installation begins.
Once installed, the tuning picture changes as well. An external wastegate gives the tuner more precise control over boost onset, peak pressure, and boost curve shape than an internal gate allows. This additional precision is part of why high-power builds run external wastegates even when boost creep is not yet an issue: the control it provides lets the tuner optimize the boost curve more effectively than a factory-style internal system allows. A professional custom tune is required after any wastegate change to calibrate the new boost control setup correctly.
7 PSI vs 14 PSI Spring
The CompGate40 is available in both a 7 PSI and a 14 PSI base spring version. The spring determines the pressure at which the wastegate opens without any boost controller signal applied. For most WRX and STI builds targeting 20 PSI and above on a boost controller solenoid, the 14 PSI spring provides a more appropriate base pressure floor. The 7 PSI version suits lower boost applications or setups where the boost controller has a wider duty cycle range and the builder wants more electronic control over the full boost window. If there is uncertainty about which spring suits the specific build and boost controller, the tuner making the calibration is the right person to consult before ordering.
What to Pair With This Upgrade
An external wastegate works as part of a complete boost control system. A boost controller manages the solenoid signal that modifies the wastegate’s spring pressure, allowing the tuner to set boost targets above the base spring rating. Without a boost controller, the wastegate opens at the spring pressure only, which limits how high boost can be pushed above the base rating.
For builds where the wastegate is part of a larger turbo upgrade, the turbochargers category covers large-frame options that commonly pair with external wastegate setups on WRX and STI builds. The intercooler kits category covers charge air cooling, which becomes more important as boost increases. For a full picture of how the wastegate fits into a turbo build on the WRX platform, the post on how boost control and forced induction work on WRX and STI covers the complete boost control system from turbo through wastegate through intercooler.
Shop the Turbosmart CompGate40 External Wastegate
The Turbosmart 40mm CompGate40 External Wastegate ships in 24 to 48 hours. Available in Blue, Black, Purple, and Red at $393.95.
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