Wastegate & Blow-Off Valve FAQ: Turbo Boost Control Questions Answered

If you're building or upgrading a turbocharged vehicle, two of the most important components to understand are the wastegate and the blow-off valve, commonly called a BOV.

Both help control pressure in a forced-induction system, but they perform completely different jobs. This FAQ answers some of the most common questions about turbo wastegates, blow-off valves, boost control, compressor surge and choosing the right components for your setup.

Granatelli Motor Sports offers 44mm, 50mm and 60mm external wastegates, piston-actuated and water-cooled wastegate options, 50mm blow-off valves and the 64mm Anaconda high-flow BOV for serious street and racing applications.

Wastegate FAQ

What Does a Wastegate Do?

A wastegate controls how much exhaust energy reaches the turbocharger turbine.

When the wastegate opens, it allows some exhaust gas to bypass the turbine. This helps regulate turbocharger speed and maintain the desired boost pressure.

In simple terms: the wastegate controls boost from the exhaust side of the turbo system.

Does a Wastegate Control Boost?

Yes. The wastegate is one of the primary components responsible for controlling boost pressure on a turbocharged engine.

The wastegate spring establishes the mechanical base boost level, while additional boost-control hardware can be used to command higher boost depending on the system.

What Is an External Wastegate?

An external wastegate is a separate valve installed in the exhaust system rather than being built directly into the turbocharger.

External wastegates are common on custom turbo systems because they allow the builder more flexibility with:

• Wastegate size
• Wastegate placement
• Exhaust bypass flow
• Boost-control strategy
• Turbo manifold design

What Is the Difference Between an Internal and External Wastegate?

An internal wastegate is built into the turbocharger housing.

An external wastegate is a separate component mounted in the exhaust system.

Internal wastegates are common on factory turbo systems, while external wastegates are frequently used on custom and high-performance turbo builds where additional exhaust-flow control is required.

What Size Wastegate Do I Need?

There is no single wastegate size that is correct for every turbo system.

Wastegate sizing depends on several factors, including:

• Engine displacement
• Turbocharger size
• Desired boost pressure
• Exhaust manifold design
• Wastegate placement
• Single or twin turbo configuration
• Exhaust flow
• Horsepower target

Granatelli Motor Sports offers several external wastegate sizes, including 44mm, 50mm and 60mm.

Is a Bigger Wastegate Always Better?

No.

A larger wastegate can bypass more exhaust, but that does not mean the largest possible wastegate is automatically the correct choice for every engine.

The goal is to select a wastegate that provides the amount of exhaust bypass flow required for the specific turbo system.

What Is Boost Creep?

Boost creep occurs when boost pressure continues increasing beyond the intended target, often because the system cannot bypass enough exhaust around the turbocharger turbine.

Wastegate size, placement, exhaust-manifold design and exhaust flow can all influence boost control.

Does Wastegate Location Matter?

Yes.

A wastegate needs to receive enough exhaust flow to effectively control the turbocharger. Poor wastegate placement can make boost control more difficult even if the wastegate itself is large enough.

Wastegate placement should be considered during the design of the turbo manifold rather than treated as an afterthought.

What Is a Piston-Actuated Wastegate?

Granatelli Motor Sports offers piston-actuated external wastegates in multiple sizes.

Instead of relying on a conventional flexible diaphragm for valve actuation, the piston design uses a mechanical piston assembly to control wastegate operation.

What Is a Water-Cooled Wastegate?

A water-cooled wastegate incorporates coolant passages around the actuator area to help manage temperature.

This can be useful on tightly packaged turbo systems where the wastegate is positioned close to extremely hot exhaust components.

Granatelli Motor Sports offers water-cooled wastegate options for builders who want additional thermal management.

What Do Wastegate Springs Do?

The wastegate spring establishes the mechanical base boost pressure.

Granatelli wastegate packages are available with spring options including 7 PSI and 14 PSI depending on the wastegate configuration.

A boost controller can then be incorporated into the system when additional boost control is required.

Can I Run More Boost Than the Wastegate Spring?

Yes, depending on the boost-control system.

The wastegate spring establishes base pressure, while electronic or manual boost-control systems can be used to command additional boost above that level.

Boost settings should always be appropriate for the engine, fuel system, turbocharger and tune.

Blow-Off Valve FAQ

What Does a Blow-Off Valve Do?

A blow-off valve releases compressed air from the charge system when the throttle closes.

When the engine is under boost, compressed air is moving through the charge piping toward the throttle body. If the throttle suddenly closes, that air needs somewhere to go.

The BOV opens and provides a controlled pressure-release path.

The BOV controls pressure on the intake side of the turbo system.

What Does BOV Stand For?

BOV stands for Blow-Off Valve.

The terms BOV, turbo BOV and blow-off valve are commonly used interchangeably.

Does a Blow-Off Valve Add Horsepower?

A blow-off valve does not directly create horsepower.

Its purpose is pressure management. A properly selected BOV helps release trapped compressed air when the throttle closes.

What Is Compressor Surge?

Compressor surge can occur when airflow through the turbocharger compressor becomes unstable.

One situation where this can happen is when the throttle closes while the turbocharger is still producing pressure. The trapped air can push back toward the compressor.

A properly functioning BOV helps release this pressure when the throttle closes.

Is Turbo Flutter the Same as a Blow-Off Valve Sound?

Not necessarily.

A blow-off valve sound is created by compressed air being released through the BOV.

Flutter can be associated with pressure interacting with the compressor when the throttle closes. Because different turbo systems behave differently, sound alone should not be used to determine whether a BOV is operating correctly.

What Size Blow-Off Valve Do I Need?

BOV sizing depends on how much compressed air the forced-induction system is moving.

Important factors include:

• Turbocharger size
• Boost pressure
• Engine displacement
• Horsepower level
• Charge-pipe diameter
• Charge-system volume
• Single or twin turbo configuration

Granatelli Motor Sports offers 50mm BOV options as well as the 64mm Anaconda high-flow blow-off valve for high-airflow applications.

Is a Bigger Blow-Off Valve Better?

Not automatically.

A larger BOV can provide greater airflow capacity, but the correct valve should be matched to the airflow and pressure requirements of the forced-induction system.

A high-horsepower turbo combination may require more pressure-relief capacity than a mild street turbo system.

What Is the Granatelli Viper Series BOV?

The Granatelli 540198 Viper Series is a 50mm high-flow vent-to-atmosphere blow-off valve.

Its externally adjustable spring preload allows the BOV response to be tailored to the vacuum and boost characteristics of the individual turbo system.

Key Viper Series specifications include:

• 50mm valve size
• Adjustable spring preload
• Vent-to-atmosphere discharge
• Billet aluminum construction
• Universal custom turbo application

What Is the Granatelli Anaconda BOV?

The Granatelli 64mm Anaconda Blow-Off Valve is designed for high-airflow forced-induction applications.

Its large 64mm valve provides substantial pressure-relief capacity for serious turbocharged builds.

The Anaconda is a strong option for builders using large-frame turbochargers, high boost or other applications moving large volumes of compressed air.

What Does Vent-to-Atmosphere Mean?

A vent-to-atmosphere BOV releases compressed air directly outside the charge system when the valve opens.

This creates the distinctive pressure-release sound commonly associated with performance turbo vehicles.

Can I Use an Atmospheric BOV on a MAF Vehicle?

It depends on the engine-management strategy.

On some mass-airflow-metered vehicles, the engine-management system has already measured the air before the BOV releases it. Venting that measured air into the atmosphere can affect drivability on some applications.

Before installing an atmospheric BOV, verify that the vehicle's engine-management configuration is compatible with atmospheric venting.

Where Should a Blow-Off Valve Be Installed?

A blow-off valve is installed in the turbocharger charge piping.

The ideal location depends on:

• Turbocharger location
• Intercooler placement
• Throttle-body location
• Charge-pipe design
• Available mounting space
• Vacuum reference routing

How Do You Adjust an Adjustable BOV?

An adjustable BOV should be set according to the vacuum and boost characteristics of the specific engine.

On the Granatelli Viper Series, the externally adjustable spring preload allows the installer to fine-tune valve response.

The goal is to have the valve remain closed when it should be sealed while still responding properly when pressure needs to be released.

Wastegate vs. Blow-Off Valve FAQ

Is a Wastegate the Same Thing as a Blow-Off Valve?

No.

They perform completely different jobs.

Wastegate = controls exhaust flow and turbo boost.

Blow-off valve = releases compressed intake pressure when the throttle closes.

Do I Need Both a Wastegate and a BOV?

Most custom performance turbo systems use both because each component controls a different side of the turbo system.

The wastegate manages exhaust energy going to the turbine.

The BOV manages compressed air in the charge system when the throttle closes.

Can a BOV Control Boost Pressure?

A BOV is not intended to replace the wastegate as the primary method of controlling turbo boost.

The wastegate controls how much exhaust energy drives the turbocharger. The BOV releases charge pressure during throttle events.

Can a Wastegate Replace a Blow-Off Valve?

No.

A wastegate operates on the exhaust side of the turbo system while a BOV operates on the compressed-air side.

One component cannot simply perform the other's job.

What Should I Upgrade First: Wastegate or BOV?

That depends on the problem you are trying to solve.

If you are having trouble controlling boost pressure, the wastegate system, wastegate sizing, location and boost-control strategy should be evaluated.

If you need additional pressure-relief capacity when the throttle closes, the BOV system should be evaluated.

Do Wastegates and BOVs Need Maintenance?

Like any component exposed to heat, pressure and repeated operation, wastegates and blow-off valves should be inspected periodically.

Check:

• Mounting hardware
• V-band connections
• Vacuum and boost-reference lines
• Hoses and fittings
• Signs of leaks
• Valve movement
• Heat damage

Granatelli Motor Sports Turbo Boost-Control Components

Granatelli Motor Sports offers multiple boost-control options for custom turbo systems, including:

• 44mm external wastegates
• 50mm external wastegates
• 60mm external wastegates
• Piston-actuated wastegates
• Water-cooled wastegate options
• 50mm blow-off valves
• Granatelli Viper Series 50mm BOV
• Granatelli 64mm Anaconda BOV
• V-band flanges and clamps
• Turbo system accessories

The Bottom Line

Wastegates and blow-off valves are both essential boost-control components, but they solve different problems.

The wastegate controls exhaust energy and regulates turbo boost.

The blow-off valve releases compressed charge pressure when the throttle closes.

Correct sizing, placement and adjustment of both components can help create a turbo system that is easier to control and better matched to the engine, turbocharger and horsepower goals.

Shop Granatelli Wastegates & Blow-Off Valves

Explore Granatelli Motor Sports wastegates, blow-off valves and turbo boost-control components for street, street/strip and race turbo applications.

Control the boost. Control the pressure. Build the turbo system the right way.