Wastegates and Blow Off Valves + Explained Correctly and in Detail

Wastegates and Blow Off Valves Explained

What a Wastegate Does

A turbocharger is driven by exhaust gas. The more exhaust energy you send through the turbine, the faster the turbo spins. The wastegate controls this by diverting exhaust flow away from the turbine once a target boost pressure is reached.

In simple terms

  • More exhaust sent to the turbine = more boost
  • Less exhaust to the turbine = less boost

When the wastegate opens and “bleeds off” excess exhaust energy, it lowers boost.

Main Benefits of a Wastegate

Boost Control

The wastegate limits maximum boost pressure, stabilizes boost, and prevents dangerous overboost conditions. Without it, boost can climb uncontrollably with RPM and load.

Engine Protection

A properly functioning wastegate helps protect the engine from detonation, excessive cylinder pressure, lean conditions, overheating, and catastrophic failure.

Turbocharger Protection

The wastegate also helps prevent turbo overspeed. Turbochargers can spin extremely fast, and exceeding safe shaft speed can damage bearings and wheels.

Improved Power Management

Wastegates allow tuners to shape boost curves, torque delivery, traction, and drivability—especially important for drag racing, road racing, and high-horsepower street cars.

Better Efficiency

A properly sized wastegate reduces pumping losses, stabilizes turbine speed, and improves thermal management for repeatable power and reliability.

Internal vs External Wastegates

Internal Wastegate

Built into the turbocharger housing.

  • Benefits: Compact, often less expensive, quieter, OEM-friendly
  • Drawbacks: Limited flow capacity and less precise control at higher power
  • Commonly found on: Factory turbo cars and entry-level low-to-moderate power builds

External Wastegate

Separate valve mounted on the exhaust manifold or turbo piping.

  • Benefits: Superior boost control, higher flow capability, better high-RPM control
  • Drawbacks: Mostly packaging and noise (especially with a screamer pipe)
  • Commonly used in: Racing and serious aftermarket forced-induction builds

The “Wastegate Sound”

The screaming sound you hear on some race cars often comes from an external wastegate dumping exhaust to atmosphere through a screamer pipe—excess exhaust energy being bypassed.

What Is a Blow Off Valve (BOV) and What Does It Do?

A blow-off valve (BOV) protects the turbocharger/supercharger and helps maintain responsiveness when you lift off the throttle. Under boost, the compressor is pushing air forward. When you lift and the throttle closes, that pressurized air has nowhere to go—so it can slam back against the compressor wheel. This is compressor surge.

Why Compressor Surge Matters

  • Reduces stress on turbo/blower bearings
  • Helps prevent premature wear or damage
  • Improves throttle transitions and shift recovery

Performance Benefits of a Proper BOV

  • Faster response between shifts: less lag, smoother power delivery
  • Improved drivability: smoother transitions during throttle changes
  • Reduced surge noise: less “flutter/chirp/turkey gobble”
  • Stabilized compressor operation: helps maintain efficiency

Atmospheric vs Recirculating (Diverter) Valves

Atmospheric BOV

Vents air to atmosphere for the loud “whoosh.” Popular on aftermarket performance builds, but on MAF-based cars it can cause rich conditions if not tuned correctly.

Recirculating (Diverter) Valve

Routes air back into the intake system. Quieter, OEM-preferred, and typically better for MAF-based drivability and emissions compliance.

Cold-Side Pressure Relief on Centrifugal Superchargers

Centrifugal superchargers are crank-driven, so you can’t control impeller speed like a turbo does with a wastegate. Cold-side pressure relief (like the Anaconda concept) can help cap/flatten boost curves, improve traction, and reduce overboost risk while allowing more aggressive pulley ratios.

Why This Can Help

  • Allows peak boost sooner in the RPM range (depending on setup)
  • Helps prevent top-end boost runaway
  • Can improve consistency and reduce engine stress in racing

Granatelli Motor Sports Boost Control Lineup

Wastegates

  • 540261: 44mm Wastegate – Piston Actuated
  • 540203: 50mm Wastegate – Piston Actuated
  • 540260: 60mm Wastegate – Piston Actuated
  • 540244: 44mm Wastegate – Diaphragm, Water Cooled
  • 540202: 50mm Wastegate – Diaphragm, Water Cooled
  • 540259: 60mm Wastegate – Diaphragm, Water Cooled

Blow Off Valves

  • 540198: 50mm “Viper” Ultra High Flow BOV – Atmospheric
  • 540199: 64mm “Anaconda” BOV – Atmospheric
  • 540200: 50mm Mini Flow BOV – Atmospheric
  • 540201: 50mm High Flow BOV – Atmospheric