What Are Exhaust Cutouts?

Exhaust cutouts are bypass valves installed in the exhaust system between the engine and the muffler. When the valve is open, exhaust gases exit the system before reaching the muffler, creating a straight-through path that reduces backpressure. This allows the engine to expel exhaust more freely, which can unlock additional horsepower and torque while producing a deep, aggressive exhaust note. When closed, the gases follow the normal path through the muffler and catalytic converter, restoring quiet, street-legal operation. The concept has been around since the early days of hot rodding, but modern cutouts use precision-machined valves and electric actuators for reliable performance under extreme conditions.

Benefits of Installing Exhaust Cutouts on Diesel Engines and Heavy-Duty Trucks

Adding exhaust cutouts to a diesel engine or heavy-duty truck delivers several tangible advantages beyond just sound. For enthusiasts who tow heavy loads or frequently drive off-road, the ability to reduce backpressure on demand can improve throttle response and reduce exhaust gas temperatures (EGTs) during demanding situations. Here are the key benefits:

  • Increased Horsepower and Torque: By bypassing the muffler, cutouts reduce restriction, allowing the engine to breathe more freely. On turbocharged diesel engines, this can result in noticeable gains in horsepower and torque, especially in the mid-to-high RPM range.
  • Lower Exhaust Gas Temperatures: Reduced backpressure helps exhaust gases exit faster, which can lower EGTs under heavy load. This is critical for towing or climbing steep grades, as excessive heat can damage turbochargers and engine components.
  • Customizable Sound Profile: Open cutouts produce a loud, aggressive exhaust note that many diesel enthusiasts prefer for show or off-road use. With the flip of a switch, you can go from quiet highway cruising to a thundering roar.
  • Improved Fuel Efficiency: While not always dramatic, some drivers report marginal fuel economy gains when running open cutouts under certain conditions due to reduced pumping losses. Results vary based on engine tuning and driving habits.
  • Engine Braking Enhancement: Open cutouts can amplify the sound of exhaust brakes and engine braking systems, providing audible feedback that helps with trailer control on downhill sections.

Key Factors to Consider When Choosing Exhaust Cutouts

Selecting the right exhaust cutout for your diesel engine or heavy-duty truck requires careful evaluation of several factors. A poorly chosen cutout can lead to leaks, premature wear, or even performance losses. Focus on these criteria:

Material and Corrosion Resistance

Stainless steel is the gold standard for exhaust cutouts due to its ability to withstand high temperatures, road salt, and moisture. T304 stainless steel offers superior corrosion resistance compared to T409, though it comes at a higher cost. For trucks that operate in harsh environments, such as snowplows or off-road rigs, investing in a fully stainless steel cutout with a smooth internal bore reduces the risk of rust and carbon buildup that can impede valve movement.

Actuation Type: Electric vs. Manual

Electric cutouts use a motor and switch to open and close the valve, allowing for effortless operation from inside the cab. They are the most popular choice for daily drivers and performance trucks. Manual cutouts use a cable or lever system that requires stopping the vehicle to adjust. While manual units are less expensive and have fewer electrical components to fail, they are less convenient for frequent switching. For heavy-duty applications where reliability is paramount, many choose electric units from reputable brands with sealed motors and weatherproof connectors.

Size and Fitment

Cutouts must match your exhaust pipe diameter exactly to avoid leaks and flow restrictions. Common sizes for diesel trucks are 4-inch, 5-inch, and 6-inch diameters, depending on the exhaust system and engine output. Larger valves flow more volume but may require more space under the chassis. Always measure your exhaust pipe outer diameter with a caliper before ordering, and verify that the cutout’s flange pattern matches your existing system or includes adapters.

Valve Design and Flow Characteristics

The internal valve design directly affects how much restriction remains when the cutout is closed. A feather-edge valve or a streamlined butterfly design minimizes turbulence and pressure drop, ensuring that when closed, the system performs as though the cutout isn't there. Look for units with precision-machined valve plates and tight tolerances to prevent exhaust leaks that could cause drone or reduced performance.

Brand Reputation and Warranty

Brands with a long history in diesel performance, such as MBRP, MagnaFlow, Flowmaster, and Borla, typically offer better material quality, more consistent manufacturing, and customer support. A warranty of at least one year is standard, though premium brands may offer three years or more on stainless steel components. Reading owner forums and verified reviews can reveal real-world durability insights for specific truck models.

Top Exhaust Cutouts for Diesel Engines

1. MBRP Stainless Steel Exhaust Cutout

MBRP has built a strong reputation in the diesel community for their heavy-duty exhaust components. Their stainless steel cutout features a T304 stainless steel construction with a smooth-flowing internal design that minimizes turbulence when closed. The electric motor is enclosed in a rugged housing with a weather-sealed connector, making it suitable for trucks exposed to mud, snow, and rain. Users report reliable operation even after years of service, and the valve opens fully in less than two seconds. The cutout is available in 4-inch and 5-inch diameters to fit popular diesel pickup models from Ram, Ford, and Chevrolet. When open, the sound is deep and aggressive without excessive drone at highway speeds, making it a favorite for daily-driven trucks that occasionally hit the track or trails.

2. MagnaFlow Electric Exhaust Cutout

MagnaFlow’s electric cutout stands out for its precision-machined valve and silent operation motor. The unit is constructed from fully welded stainless steel with a brushed finish that resists discoloration from heat. The valve blade is laser-cut for a perfect seal, which helps maintain consistent backpressure when closed. MagnaFlow includes a wiring harness and switch kit, simplifying installation for DIY owners. On heavy-duty diesel applications, the cutout produces a clean, powerful tone that amplifies the natural diesel growl without introducing raspiness. The motor is rated for over 100,000 cycles, ensuring long-term reliability even on trucks used for towing or commercial purposes.

3. BD Diesel Exhaust Brake Cutout Combo

For diesel owners who also want exhaust braking capability, BD Diesel offers an innovative combination unit that integrates a cutout with a throttle-actuated exhaust brake. This unique design allows the cutout to serve double duty: when closed, it functions as a standard exhaust brake for enhanced downhill control; when open, it provides straight-through flow for maximum performance and sound. The housing is cast iron with a stainless steel valve plate, built to withstand extreme heat and backpressure. This option is ideal for heavy-duty pickups and medium-duty trucks used for towing large trailers or hauling heavy loads, where both braking and performance are critical.

Best Exhaust Cutouts for Heavy-Duty Trucks

1. Dynomax Ultra Flo Exhaust Cutout

Dynomax is a trusted name in the heavy-duty truck segment, and their Ultra Flo cutout is engineered for maximum flow and durability. The valve features a large-diameter bore that matches 5-inch and 6-inch exhaust systems commonly found on Class 6 and Class 7 trucks. The housing is made from heavy-gauge stainless steel with reinforced flanges to resist warping under high heat. The electric actuator uses a high-torque motor that can open the valve even with carbon buildup or debris present. Fleet operators have reported reliable performance in regional and long-haul applications, with minimal maintenance required beyond periodic cleaning. The sound when open is authoritative without being deafening, making it suitable for trucks that enter residential areas occasionally.

2. Borla Stainless Steel Exhaust Cutout

Borla brings their signature craftsmanship to the heavy-duty market with a cutout designed for maximum corrosion resistance and aesthetic appeal. The entire assembly, including the valve blade and actuator bracket, is constructed from T304 stainless steel. Borla uses a proprietary valve seal that prevents leaks at the closed position, ensuring that the truck remains quiet when the cutout is not in use. The actuator is mounted securely to withstand vibrations from diesel engines and rough road surfaces. Borla cutouts are available in 4-inch to 6-inch sizes and include a premium wiring kit with labeled connectors for straightforward installation. For heavy-duty truck owners who demand the best materials and are willing to invest accordingly, Borla delivers a polished package that performs reliably over hundreds of thousands of miles.

3. Flowmaster Outlaw Electric Cutout

Flowmaster’s Outlaw series cutout is built with the same aggressive attitude as their iconic mufflers. The housing is made from aluminized steel with a stainless steel valve plate, striking a balance between cost and durability. The electric motor is compact and mounts easily in tight chassis spaces common on heavy-duty trucks. Flowmaster includes a remote control option, allowing the driver to open or close the cutout without reaching for a dashboard switch. The sound character is deep and guttural, with a noticeable increase in volume when opened. For truck owners who want a budget-friendly but reliable cutout from a brand with decades of exhaust expertise, the Outlaw series represents excellent value.

Electric vs. Manual Exhaust Cutouts: Which Is Right for You?

Choosing between electric and manual operation depends on how you use your truck and your tolerance for complexity. Electric cutouts dominate the market because of their convenience: you can switch between quiet and loud modes while driving without pulling over. Modern electric actuators are sealed against moisture and dust, and many kits include wireless remotes for effortless control. The downsides include higher cost, potential electrical failure, and slightly slower response time compared to a direct mechanical link.

Manual cutouts are simpler, lighter, and less expensive. They typically use a stainless steel cable that connects the valve to a lever mounted under the dashboard or on the steering column. Manual operation is reliable in extreme environments where electrical components might fail, such as on trucks used in deep water crossings or extreme dust. However, you must stop the vehicle to adjust the valve, which can be inconvenient if you need to quickly quiet the truck for a weigh station or residential area. For most diesel enthusiasts and fleet operators who prioritize ease of use and safety, electric cutouts are the clear choice.

Installation Guide and Best Practices

Proper installation is critical to achieving the full benefits of exhaust cutouts and avoiding leaks or mechanical failures. Follow these steps for a successful installation:

  1. Choose the Right Location: The cutout should be installed as close to the exhaust manifold or turbo downpipe as possible while still allowing clearance for the actuator and wiring. For diesel engines, a spot between the downpipe and the catalytic converter or muffler is common. Ensure the valve can fully open without hitting the frame, driveshaft, or suspension components.
  2. Prepare the Exhaust Pipe: Measure and mark the section of pipe where the cutout will be installed. Cut the pipe using a band saw or reciprocating saw with a metal-cutting blade. Deburr the edges and clean the surrounding area to ensure a good weld or clamp seal.
  3. Weld or Clamp the Cutout: Welding provides the most secure and leak-free connection, but requires skill and proper equipment. If welding, use a stainless steel filler rod and purge the pipe interior with argon to prevent oxidation. For clamp-on installations, use high-quality band clamps designed for exhaust systems and apply a high-temperature silicone sealant to the joint.
  4. Route the Actuator Wiring: For electric cutouts, route the wiring harness away from heat sources, sharp edges, and moving parts. Use wire looms or heat-resistant sleeves to protect the wires. Connect the switch or remote receiver to a fused 12V power source with a relay to prevent overloading the motor.
  5. Test for Leaks and Operation: Start the engine and check all joints for exhaust leaks using a soapy water solution or a smoke machine. Cycle the cutout open and closed several times to verify smooth movement and full travel. Adjust the actuator linkage if necessary to ensure the valve seats completely when closed.
  6. Secure and Inspect Regularly: Tighten all bolts and clamps to the manufacturer’s torque specifications. Inspect the cutout assembly monthly for signs of corrosion, carbon buildup, or loose fasteners. Lubricate the valve pivot points with a high-temperature anti-seize compound every six months to maintain smooth operation.

Maintenance and Care for Longevity

Exhaust cutouts operate in a harsh environment with extreme temperatures, moisture, road salt, and constant vibration. Proper maintenance extends their service life and ensures reliable performance. Start by periodically checking the actuator motor for debris or corrosion, especially after off-road driving or winter months. Clean the valve blade and housing interior with a wire brush and a solvent to remove carbon deposits that can cause sticking. For electric units, test the motor movement and wiring connections at each oil change. Apply dielectric grease to electrical connectors to prevent corrosion. If you notice the cutout becoming slow to open or close, or if it fails to seat fully, disassemble the valve and inspect the pivot shaft for wear. Replacing worn bushings or seals early prevents more expensive repairs later.

Storage of the vehicle for extended periods can also affect cutout performance. If the truck will sit for more than a month, cycle the cutout open and closed a few times to prevent the valve from seizing in one position. Consider applying a light coating of high-temperature anti-seize to the valve plate edges to reduce friction. For trucks driven in coastal areas or regions with heavy road salt, investing in a cutout with a fully stainless steel housing and actuator bracket significantly reduces corrosion-related failures.

Before installing exhaust cutouts, understand the legal implications in your area. Many states and municipalities have noise ordinances that restrict vehicles from exceeding a certain decibel level, typically measured at a specific distance from the exhaust outlet. Opening a cutout can easily push noise levels past legal limits, resulting in citations or fines. Additionally, tampering with emissions control devices such as catalytic converters or diesel particulate filters is illegal under federal law in the United States and may void your vehicle’s warranty. Exhaust cutouts that bypass these components are prohibited for on-road use in many jurisdictions. Always check local laws and consider using cutouts only for off-road, track, or show purposes. Some manufacturers include a lockout feature or a removable fuse that prevents the cutout from opening when the vehicle is in certain operating conditions, which can help with compliance during inspections.

Conclusion

Exhaust cutouts offer diesel engine and heavy-duty truck owners a versatile way to enhance performance, reduce exhaust temperatures, and customize their vehicle’s sound character. Whether you choose a premium stainless steel unit from MBRP or MagnaFlow, a heavy-duty option from Dynomax or Borla, or a budget-friendly model from Flowmaster, the key is to match the cutout to your specific exhaust diameter, usage pattern, and maintenance capabilities. Electric actuation provides the convenience of on-the-fly control, while manual operation offers simplicity and ruggedness for extreme conditions. Proper installation with quality welding or clamps, combined with regular cleaning and inspection, ensures your cutout delivers reliable service for years. By considering the factors of material, size, valve design, and legal restrictions, you can select the best exhaust cutout that perfectly complements your diesel engine or heavy-duty truck build, providing the perfect balance of power, sound, and drivability.

For further reading on diesel exhaust system design and performance testing, visit the Diesel Power Products technical library or check the SAE International papers on exhaust backpressure effects for in-depth engineering data.