Do Exhaust Cutouts Add Horsepower? How Reducing Exhaust Restriction Can Improve Performance

One of the most common questions we hear about electronic exhaust cutouts is simple:

Do exhaust cutouts actually add horsepower?

The answer is:

They can — but how much depends on the engine and how restrictive the existing exhaust system is.

An exhaust cutout does not create horsepower on its own. What it can do is give exhaust gases a shorter, less restrictive path out of the vehicle.

For the right combination, reducing that restriction can help the engine produce more horsepower and torque.

That is one of the main reasons Granatelli Motor Sports developed its line of electronic, manual, round and low-profile oval exhaust cutouts.

Shop Granatelli Exhaust Cutouts

What Does an Exhaust Cutout Actually Do?

A traditional exhaust system routes exhaust gases through a series of components before they leave the vehicle.

Depending on the vehicle, that can include:

• Exhaust manifolds or headers
• Catalytic converters
• Resonators
• Mufflers
• Exhaust tubing
• Tailpipes

Each component can create some amount of restriction.

An exhaust cutout creates an alternate path.

When the cutout is closed, the vehicle operates through the normal exhaust system.

When the cutout is open, exhaust gases can exit through a shorter path before traveling through some of the downstream exhaust components.

That can reduce restriction.

Watch a Granatelli Electronic Exhaust Cutout in Action

See how a Granatelli electronic exhaust cutout operates and how quickly you can change the sound and exhaust path of the vehicle.

Watch this Granatelli exhaust cutout video on YouTube

Why Exhaust Restriction Matters

After combustion, the engine has to push exhaust gases out of the cylinder.

The harder the engine has to work to move those gases through the exhaust system, the more energy can be consumed during the exhaust stroke.

This is commonly discussed in terms of exhaust backpressure.

Technical research has shown that excessive exhaust backpressure can negatively affect engine power and torque.

That supports the basic engineering principle behind using an exhaust cutout for performance:

Reduce unnecessary exhaust restriction when maximum flow is needed.

Read the SAE technical study on exhaust backpressure

Does That Mean Backpressure Is Always Bad?

This topic gets misunderstood all the time.

You will often hear someone say:

“An engine needs backpressure to make torque.”

That is not really the right way to look at it.

A properly designed exhaust system depends on exhaust velocity, pipe diameter, pressure-wave behavior, scavenging and many other factors.

Simply adding restriction is not what makes torque.

An exhaust system that is too large can hurt performance for other reasons, particularly on naturally aspirated engines.

But that does not mean an engine benefits from forcing exhaust through an unnecessarily restrictive muffler or exhaust system.

The goal is an exhaust system that flows correctly for the engine.

When Can an Exhaust Cutout Make the Biggest Difference?

The more restrictive the existing exhaust system is relative to the engine's airflow requirements, the greater the potential benefit from opening a cutout.

High-Horsepower Engines

A 700-horsepower engine moves considerably more air and exhaust than a 250-horsepower engine.

As airflow increases, restrictions in the exhaust system can become more significant.

Supercharged Engines

A supercharger forces additional air into the engine.

More air plus more fuel means more exhaust gas has to leave the engine.

Reducing downstream exhaust restriction can become increasingly important as boost and horsepower increase.

Turbocharged Engines

Turbocharged engines also move large amounts of exhaust gas.

The exhaust gases must first drive the turbocharger turbine, but restriction after the turbine can still affect overall system performance.

A properly positioned exhaust cutout downstream of the turbo can provide a less restrictive exhaust path when opened.

Nitrous Engines

Nitrous allows the engine to burn considerably more fuel and oxygen.

That creates more combustion energy — and more exhaust volume.

Large-Displacement Naturally Aspirated Engines

Big-blocks, large LS engines, Coyotes, Hemis and other high-output naturally aspirated combinations can also benefit when the existing exhaust becomes a restriction.

What About a Stock Engine?

A mostly stock vehicle may or may not show a significant horsepower increase.

If the factory exhaust already flows adequately for the engine's output, there may not be much restriction to remove.

That does not mean the cutout is useless.

Many customers install electronic cutouts because they want:

A much more aggressive exhaust sound on demand.

The potential horsepower benefit is an added advantage.

Why Horsepower Gains Vary

It would be misleading to say every vehicle gains a specific amount of horsepower from an exhaust cutout.

There are too many variables.

• Engine displacement
• Horsepower level
• Existing exhaust diameter
• Muffler design
• Resonator design
• Headers
• Catalytic converters
• Turbocharger configuration
• Supercharger setup
• Camshaft
• Engine RPM
• Cutout size
• Cutout location
• Tuning

A vehicle with a highly restrictive exhaust may see a measurable performance difference.

A vehicle already running a properly sized free-flowing exhaust may see a smaller change.

Cutout Location Matters

Where the exhaust cutout is installed can have a major effect on what it bypasses.

For most street applications, a cutout is generally positioned downstream of emissions equipment.

Granatelli states that when its cutout system is installed after the catalytic converter, it does not require a computer reflash or custom tune simply because of the cutout installation.

Learn more about Granatelli Exhaust Cutouts

Always check applicable local, state and federal emissions and noise regulations before installing or operating an exhaust cutout.

Bigger Isn't Automatically Better

Just like an exhaust system, cutout size should be appropriate for the vehicle.

Granatelli offers cutouts for several popular exhaust diameters, including:

• 2.25-inch
• 2.5-inch
• 3-inch
• 3.5-inch
• 4-inch

The correct size depends on the existing exhaust tubing and engine combination.

Installing a 4-inch cutout on a mild engine with a 2.5-inch exhaust system does not magically create more horsepower.

The goal is to provide an effective alternate exhaust path without compromising the rest of the system.

Single vs. Dual Exhaust Cutouts

A single-exhaust vehicle will typically use one cutout.

A true dual-exhaust vehicle may use two.

With a dual system, each bank of the engine can have its own cutout.

Granatelli offers complete single and dual systems so the cutouts can be matched to the vehicle's exhaust configuration.

View Granatelli Electronic Exhaust Cutouts

See How a Granatelli Slip-Fit Exhaust Cutout Is Installed

This Granatelli Motor Sports video shows an electronic slip-fit exhaust cutout being installed and demonstrated on a truck.

Watch the Granatelli slip-fit exhaust cutout installation on YouTube

What Makes a Granatelli Electronic Cutout Different?

Performance is only part of the equation.

An electronic cutout also has to survive underneath a vehicle where it is constantly exposed to:

• Exhaust heat
• Water
• Road debris
• Vibration
• Dirt
• Repeated heat cycles

CNC-Machined 6061 Aluminum Bodies

The cutout body is CNC-machined from lightweight, durable 6061 aluminum.

Stainless-Steel Butterfly Plate and Shaft

Stainless components are used in the exhaust-flow area to handle the demanding environment.

High-Torque Gear-Reduction Motor

The motor is designed to fully open and close the butterfly valve.

One-Touch Smart-Chip Control

Some electronic cutouts require you to hold the switch while the valve travels.

Granatelli's one-touch system allows you to push the switch and let the controller complete the operation.

The automatic-stop design helps prevent the motor from continuing to drive the butterfly after it reaches the end of its travel.

360-Degree V-Band Adjustment

The V-band design allows the cutout and exhaust turndown to be rotated during installation.

This provides more flexibility around:

• Frames
• Floor pans
• Driveshafts
• Suspension components
• Crossmembers

45-Degree Stainless-Steel Turndown

The turndown helps direct exhaust gases away from the underside of the vehicle rather than simply dumping them straight down.

See Granatelli Exhaust Cutouts at SEMA

Granatelli Motor Sports has also demonstrated the electronic exhaust cutout system at SEMA, showing the construction, operation and features of the system.

Watch Granatelli Exhaust Cutouts at SEMA on YouTube

Why an Electronic Cutout Makes Sense on a Street/Strip Car

A street/strip vehicle presents a problem.

You may want a comfortable exhaust system when:

• Driving to work
• Cruising on the highway
• Taking the family somewhere
• Leaving the house early in the morning

But at the track or car event you may want:

• More exhaust sound
• Reduced restriction
• Maximum exhaust flow

An electronic cutout lets the same exhaust system do both.

Street Mode

Cutout closed.

Exhaust continues through the normal mufflers and tailpipes.

Performance Mode

Cutout open.

Exhaust gets an alternate, potentially less restrictive path.

One vehicle. Two completely different personalities.

What About Lowered Cars?

Traditional round cutouts can present ground-clearance problems on lowered vehicles.

That is why Granatelli developed its 3-inch oval electronic exhaust cutout.

The oval design is approximately 2.25 inches tall, providing roughly 0.75 inch additional ground clearance compared with a traditional 3-inch round tube configuration.

You still get the flow characteristics of a 3-inch system without hanging a large round cutout as far underneath the car.

That makes the oval system particularly useful for:

• Lowered Camaros
• Corvettes
• Mustangs
• Pro Touring cars
• Custom builds
• Street/strip vehicles

See Granatelli Oval Exhaust Cutouts

Will Opening the Cutout Make the Car Louder?

Absolutely.

In many applications, dramatically louder.

Opening a cutout can bypass much of the equipment designed to reduce exhaust noise.

That is part of the appeal.

But it is also why drivers should understand local noise laws before using an open cutout on public roads.

At the track? That's where things get fun.

Do You Need a Tune After Installing an Exhaust Cutout?

For Granatelli systems installed after the catalytic converter, Granatelli states that a computer reflash or expensive custom tune is not required simply for installation of the cutout.

Highly modified vehicles may still benefit from tuning for the overall engine combination, but that is different from saying the cutout itself automatically requires a tune.

So, Do Exhaust Cutouts Add Horsepower?

The most accurate answer is:

An exhaust cutout can increase horsepower and torque when opening it significantly reduces a restriction in the exhaust system.

The more airflow the engine requires and the more restrictive the downstream exhaust is, the greater the potential benefit.

That is why exhaust cutouts can be especially valuable on:

• High-horsepower builds
• Turbo cars
• Supercharged cars
• Nitrous combinations
• Large-displacement engines
• Street/strip vehicles

But even when horsepower isn't the main objective, an electronic cutout offers something enthusiasts appreciate immediately:

Control over how the car sounds.

Quiet when you need it.

Wide open when you want it.

The Bottom Line

There is no universal horsepower number that applies to every exhaust cutout installation.

The engine determines how much exhaust needs to move.

The existing exhaust determines how much restriction is present.

The location and size of the cutout determine how much restriction can be bypassed.

The engineering principle, however, is straightforward.

Reducing excessive exhaust restriction can help support horsepower, torque and overall engine efficiency.

Granatelli combines that idea with:

• One-touch electronic control
• Automatic-stop operation
• CNC-machined 6061 aluminum construction
• Stainless-steel butterfly components
• 360-degree adjustable V-band connections
• 45-degree stainless-steel turndowns
• Round and low-profile oval options
• Single and dual systems
• Multiple exhaust diameters

So the question isn't simply:

“Will an exhaust cutout make my car louder?”

The better question is:

“How much restriction is my current exhaust creating when my engine is trying to make maximum power?”

Shop Granatelli Electronic Exhaust Cutouts

Explore Granatelli electronic, manual, round, oval, single and dual exhaust cutout systems.

Shop Granatelli Motor Sports Exhaust Cutouts

Technical Reference

SAE International — Study to Improve Engine Efficiency by Reducing Backpressure:

SAE Exhaust Backpressure Research