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

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.

Depending on where the cutout is installed, opening it may allow exhaust to bypass:

• Mufflers
• Resonators
• Long sections of exhaust tubing
• Restrictive bends
• Tailpipes

The result is a shorter and potentially much less restrictive exhaust path.

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

Your Exhaust Has to Flow What Your Engine Produces

An engine is essentially an air pump. Air enters through the intake system, mixes with fuel, burns inside the cylinder, and then has to leave through the exhaust. The more horsepower the engine makes, the more airflow it generally has to process. Think about the difference between:

• A 300 HP naturally aspirated street engine
• and
• A 900 HP supercharged or turbocharged engine.

They may both have a 3-inch exhaust system, but the amount of exhaust gas trying to travel through that system can be dramatically different. An exhaust system that flows perfectly well at 300 horsepower may eventually become a restriction as engine output increases.

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. As exhaust gases move through the exhaust system, they encounter resistance. That resistance can come from:

• Mufflers
• Resonators
• Catalytic converters
• Pipe diameter
• Tight bends
• Crush-bent tubing
• Exhaust transitions
• Restrictions inside mufflers
• Small tailpipes
• Turbocharger exhaust systems
• Other exhaust components

When the exhaust cannot move through the system freely enough, pressure builds upstream. This is commonly discussed in terms of exhaust backpressure. SAE International has published research showing that increased exhaust backpressure can negatively affect engine power and torque, while reducing excessive backpressure can create opportunities for improved engine performance and efficiency.

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. It is one of the biggest myths in performance exhaust. You will often hear someone say:

• “An engine needs backpressure to make torque.”
• That is not really the right way to look at it. What an engine really needs is a properly designed exhaust system.

A properly designed exhaust system depends on exhaust velocity, pipe diameter, pressure-wave behavior, scavenging, collector design, cam timing, RPM range, engine displacement and many other factors. Simply adding restriction is not what makes torque. In fact, excessive backpressure can force the engine to work harder to push exhaust gases out of the cylinder. 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 isn't necessarily zero restriction everywhere. The goal is an exhaust system that flows correctly for the engine and power level.

Why Restriction Becomes More Important at Wide-Open Throttle

Your engine may make great power at part throttle, sound good on the street, and feel strong during normal driving. During normal cruising, your engine is only producing a fraction of its maximum horsepower. The exhaust system may have no problem handling that airflow. But put the throttle to the floor and everything changes. Cylinder filling increases. Fuel demand increases. Combustion energy increases. Exhaust volume increases. RPM climbs. Suddenly the exhaust system that seemed perfectly adequate while cruising may become one of the restrictions limiting maximum power.

That is why some exhaust changes show relatively little difference during normal driving but produce measurable differences on a chassis or engine dyno at wide-open throttle.

Where Can the Restriction Come From?

It isn't always the exhaust pipe itself. For example, you might already have a 3-inch exhaust system. That sounds like plenty of flow. But your exhaust could still contain:

• A restrictive muffler
• Multiple resonators
• Sharp bends
• Reducers
• A restrictive Y-pipe
• Small tailpipes
• Poor transitions
• Each component contributes to the total pressure drop through the system.

Research summarized in engineering literature has found that mufflers and resonators can account for a significant portion of exhaust-system pressure drop. That means simply having large-diameter tubing does not automatically mean the entire exhaust system is free flowing.

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. Imagine modifying a car over several years. Originally:

• 450 HP
• Then:
• 550 HP
• Then:
• 700 HP
• Then:
• 850 HP
• The same exhaust system may remain underneath the car through every stage.

At some point, the exhaust that worked perfectly with the original combination can begin restricting the new combination. Opening a cutout can provide an alternate path without requiring the car to permanently run an extremely loud race-style exhaust.

Supercharged Engines

A supercharger forces additional air into the engine. More air plus more fuel means more exhaust gas has to leave the engine. A system that works perfectly on a naturally aspirated engine may become restrictive after a supercharger is installed. Reducing downstream exhaust restriction can become increasingly important as boost and horsepower increase, and opening a cutout can provide additional exhaust-flow capacity when the engine needs it most.

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. After the turbine, reducing unnecessary restriction can help improve the pressure differential across the turbine. A restrictive exhaust downstream of the turbo can work against the system. This is why large downpipes and free-flowing exhaust systems are common on high-horsepower turbo combinations. 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. When the nitrous system activates, the engine can suddenly produce substantially more horsepower than it does during normal driving, so the exhaust system suddenly has to move considerably more exhaust gas. An exhaust cutout provides a way to increase available exhaust flow only when you want maximum performance.

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. Large displacement engines, aggressive camshafts, high RPM, ported cylinder heads, larger throttle bodies and intake modifications can all increase airflow. But with naturally aspirated combinations, exhaust sizing and scavenging can be especially important. This is why testing is better than assuming. Run the vehicle both ways. Closed vs. open. Let the dyno tell you what the engine wants.

What About a Stock Engine?

A mostly stock vehicle may or may not show a significant horsepower increase. An exhaust cutout cannot remove a restriction that isn't there. 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. If your exhaust is becoming restrictive at high RPM and maximum engine load, opening a properly positioned cutout can potentially free up power. The bigger the difference between:

• Exhaust flow required by the engine
• and
• Exhaust flow capacity of the existing system
• the greater the potential benefit.

How Do You Know If Your Exhaust Is Restrictive?

There are several ways.

1. Chassis Dyno Testing

One of the best methods is extremely simple. Make a dyno pull with the cutouts closed. Then open the cutouts and make another pull under comparable conditions. Compare:

• Peak horsepower
• Peak torque
• Horsepower curve
• Torque curve
• Air/fuel ratio
• Boost
• RPM

If horsepower increases with the cutouts open, your normal exhaust configuration was likely creating some measurable restriction at that operating point. Even more interesting is where in the RPM range the difference begins. You may find both configurations make nearly identical power at lower RPM. Then as airflow increases, the open-cutout run begins pulling away.

That can be a strong indication that exhaust restriction was increasing as the engine approached maximum output. Don't only look at the biggest number on the dyno sheet. Look at the entire curve. An exhaust change might produce:

• No difference at 3,000 RPM
• A small improvement at 4,500 RPM
• A larger improvement at 6,000 RPM
• That tells you something valuable.

It suggests exhaust demand is beginning to exceed the capacity of the closed system as RPM and airflow increase. For racing, that additional power at the top of the RPM range may be exactly where you need it.

2. Measure Exhaust Backpressure

For a more technical approach, exhaust pressure can be measured. A pressure sensor or gauge can be installed at an appropriate location in the exhaust system. Then the engine can be tested under load. The important thing isn't just looking at pressure during idle. You want to know what happens when the engine is:

• At high RPM
• Under heavy load
• Making maximum horsepower

Exhaust restriction that isn't noticeable at idle may become substantial at wide-open throttle.

3. Use the Cutout as a Diagnostic Tool

This may be one of the most overlooked benefits. If the vehicle has electronic cutouts, you have a very useful built-in testing tool. Closed:

• Full exhaust system
• Open:
• Reduced downstream exhaust restriction

If you've continued modifying your engine and you're wondering whether the exhaust has become restrictive, the cutouts can help answer that question. Make a controlled test. Cutouts closed: 610 RWHP Open them. Cutouts open: 610 RWHP Your current exhaust probably isn't costing much power at that output level.

But imagine this:

• Closed: 610 RWHP
• Open: 635 RWHP
• Now you have something worth investigating.
• The cutout didn't magically create 25 horsepower.

It exposed horsepower that the engine was already capable of producing but couldn't fully realize through the more restrictive exhaust path. Your actual results will vary, which is why testing your specific combination is so valuable. This is one of the reasons a cutout can be more than a sound modification.

How Much Restriction Is Too Much?

There isn't one universal backpressure number that applies to every engine. Different engines, turbo systems, camshafts, exhaust designs and operating speeds react differently. Instead of chasing one universal number, look at what your particular engine is telling you. Ask:

• Does horsepower continue climbing normally?
• Does opening the exhaust change the power curve?
• Does boost change?
• Does torque improve?
• Does the engine pull harder at higher RPM?
• What does measured exhaust pressure show?

Those answers are more useful than assuming every engine wants exactly the same exhaust configuration.

Cutout Location Matters

Where the exhaust cutout is installed can have a major effect on what it bypasses. The farther upstream the cutout is installed, the more downstream exhaust components it may bypass. 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.

Installation location also needs to consider:

• Catalytic converters
• Ground clearance
• Floor pan clearance
• Driveshaft
• Transmission
• Crossmembers
• Suspension travel
• Exhaust heat
• Wiring
• Exhaust direction

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 DC Gear-Reduction Motor

The motor is designed to fully open and close the butterfly valve, and it is paired with high-temperature steel drive gears.

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. Granatelli designed this system to help prevent unnecessary over-torquing of the butterfly shaft and internal drive gears.

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.

Plug-and-Play Wiring and Multiple Configurations

Depending on the system, Granatelli electronic cutouts also feature plug-and-play wiring and are offered in single and dual, slip-fit and weld-in, and round and oval configurations.

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

You could build a completely open race exhaust. But then you'd have to live with it everywhere. 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. Driving around town or on the highway, you keep your mufflers and quieter exhaust note.

Performance Mode

Cutout open. Exhaust gets an alternate, potentially less restrictive path. At a car show and want more sound? Open them. On the dyno and want to see if the exhaust is restricting power? Open them. At the drag strip and want maximum available exhaust flow? Open them. One vehicle. Two completely different personalities. You don't have to permanently choose between a street exhaust and an open race exhaust.

Your Mufflers May Be Perfect for the Street and Restrictive at the Track

A muffler isn't necessarily "bad" because it creates some restriction. For a street car, you may intentionally choose a muffler that keeps the vehicle comfortable. You might want:

• Less drone
• Lower cruising noise
• A quieter cold start
• A comfortable interior
• Then when you go racing, your priorities change.
• Now you want maximum exhaust flow.
• That's exactly where an electronic cutout makes sense.
• You don't have to replace the street exhaust.
• You simply give the exhaust another way out when maximum performance matters.

What About Lowered Cars?

Traditional round cutouts can present ground-clearance problems on lowered vehicles. A traditional 3-inch round tube is approximately 3 inches tall before considering additional hardware. 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
• Custom exhaust systems
• 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.

And unlike permanently installing an extremely loud exhaust system, an electronic cutout lets you close everything back up when the race is over.

The Bottom Line

Your exhaust system has one major job: move the exhaust gas produced by the engine. As horsepower increases, that job becomes more demanding. 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?” Or put another way: “Is my current exhaust restricting the horsepower my engine is already capable of making?” Because an exhaust cutout doesn't manufacture horsepower. It gives exhaust gases another path, and a simple way to find out whether your current exhaust is holding your engine back. So the next time you're chasing more horsepower, don't only look at what's going into the engine. Ask what may be stopping everything from getting back out.

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

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Written by JoJo Granatelli — third generation at Granatelli Motor Sports in Oxnard, California, and the one who drives what the company builds. He set a quarter-mile record of 7.06 seconds at 157 mph at Famoso Dragstrip in August 2026. More about JoJo.