Why Install an Exhaust Cutout System

An exhaust cutout gives you the ability to bypass the muffler and other restrictive components in your exhaust system with the flip of a switch (or the turn of a manual valve). This transforms your car from a quiet, daily-friendly cruiser into a raw, open-exhaust beast in seconds. The benefits go beyond sound: opening the cutout reduces backpressure, allowing the engine to exhale more freely. This can unlock a measurable gain in horsepower and torque, particularly in turbocharged or high-performance naturally aspirated engines. For enthusiasts who track their cars but still drive them on the street, a cutout is a practical compromise—you keep the stock exhaust for commuting and unleash the full-flow setup at the track or during spirited driving.

However, designing and installing a custom exhaust cutout system requires careful planning, quality components, and attention to safety and legality. A poorly executed setup can lead to exhaust leaks, drone, failed valves, or even carbon monoxide entering the cabin. This guide provides a comprehensive look at every phase of the project, from selecting the right type of cutout to final testing and compliance with local regulations.

Types of Exhaust Cutouts

Before drawing up a parts list, you need to decide which style of cutout fits your goals, budget, and technical comfort level. There are three primary categories.

Manual Cutouts

Manual cutouts use a simple butterfly or gate valve that you operate by turning a knob or lever. A cable or rod runs from the valve to a control point accessible from the driver’s seat (often through a hole drilled in the floorboard or a bracket mounted in the cabin). These are the most affordable option, typically $20 to $60. They are also the most reliable, because there are no electronic components to fail. The downside: you have to reach down and manually adjust the valve, which can be inconvenient and requires you to find a safe place to stop. Manual cutouts are best for dedicated track cars or weekend toys where inconvenience is not a primary concern.

Electronic (Electric Motor) Cutouts

Electronic cutouts are the most popular choice for street-driven cars. A small electric motor rotates the butterfly valve when you press a button or toggle a switch inside the cabin. Many systems include a remote control or a smartphone app interface. Quality electronic cutouts range from $100 to $300. Installation requires running 12V power and a ground wire to the valve, and wiring a switch somewhere convenient. Some aftermarket controllers offer additional features like partial opening positions (e.g., 25%, 50%, 75%) for fine-tuning the sound and backpressure. Reliability depends heavily on the valve’s weather sealing and motor quality. Look for brands that use sealed motors and stainless steel housings.

Vacuum-Operated Cutouts

Vacuum-actuated cutouts use engine vacuum or an external vacuum pump to open and close the valve. A solenoid controls vacuum flow to a diaphragm actuator. These were popular decades ago but have largely been replaced by electronic units. They can still be found in some OEM variable-exhaust systems. Vacuum systems are quieter in operation than electric motors but require additional plumbing, a vacuum reservoir, and tend to be more prone to leaks and diaphragm failure. For most custom builds, electronic cutouts offer the best balance of convenience, cost, and reliability.

Placement in the Exhaust System

Where you position the cutout has a significant impact on performance and sound. The ideal location depends on your goals and the layout of your exhaust.

Pre-Muffler Cutout

This is the most common placement. The cutout is installed in the exhaust pipe before the muffler (and often after the catalytic converter). When open, exhaust bypasses the muffler entirely, producing the loudest possible sound. For turbo cars, placing the cutout before the muffler but after the turbo allows the turbo to control boost response while still reducing restriction downstream. Many enthusiasts place the cutout in the mid-pipe where the pipe diameter is compatible with common cutout sizes (2.5 in or 3 in).

Pre-Catalytic Converter Cutout

In some setups, the cutout is installed between the exhaust manifold/headers and the catalytic converter. This allows exhaust to exit before reaching the cat. Warning: this is illegal in most jurisdictions because it defeats emissions control systems. It produces maximum sound and power gains but will cause check engine lights on OBD-II vehicles (due to missing catalyst monitors) and can result in hefty fines during emissions testing. This placement is generally only used for off-road or race-only vehicles.

Axe or Splitter Placement

Some cutout systems are designed as Y-pipes that split the exhaust flow. One branch goes through the muffler, the other goes through the cutout. This allows part of the exhaust to always flow through the muffler for a base level of noise reduction, even when the cutout is open. The sound may be less raw but still significantly louder than closed. This is a good option for drivers who want a more gradual change rather than a binary loud/quiet switch.

Choosing the Right Components

Building a reliable cutout system requires selecting materials that can withstand extreme heat (typically 500–1200°F at the cutout location in non-turbo cars, and up to 1600°F near headers) and corrosive exhaust condensate.

Valve Material and Construction

  • Stainless steel (304 or 316): Best corrosion resistance and longevity. Slightly more expensive but strongly recommended for any vehicle driven in wet or salty conditions.
  • Mild steel (carbon steel): Cheaper but prone to rust. Acceptable for dry-climate or race-only cars if you treat the interior with high-temp paint.
  • Butterfly valve vs. gate valve: Most aftermarket cutouts use a butterfly valve because it is compact and creates minimal obstruction when open. Gate valves offer a straight-through path when open but are bulkier and more expensive.
  • Seal quality: Look for valves with a machined seat and a flexible seal (silicone or graphite) around the butterfly. Metal-on-metal seals often leak and rattle.

Gaskets and Sealant

Use high-temperature exhaust gaskets (made from multi-layer steel or graphite) at the flanged connections where the cutout meets the existing exhaust pipe. Copper spray gasket can be applied to both sides of the gasket for an extra leak barrier. For slip-fit connections, use stainless steel clamps designed for exhaust systems (e.g., band clamps or V-band clamps). Do not use standard U-bolt clamps on a cutout because they can crush the thin-walled pipe and cause leaks.

Wiring and Switch (Electronic Systems)

Run a dedicated 12V power wire from the battery or a fused ignition-switched source to the cutout motor. The motor draws a small current (typically 2–5 amps), so 18-gauge wire is sufficient, but use 16-gauge for longer runs. The switch should be mounted in a dry location accessible without reaching awkwardly. Some kits include a relay to protect the switch contacts. A fully sealed toggle or rocker switch is ideal. For remote control operation, ensure the receiver antenna is positioned well to get a clear signal inside the cabin.

Step-by-Step Installation

These instructions assume a generic pre-muffler electronic cutout installation. Adapt as needed for your specific vehicle and cutout type.

1. Determine Exact Location and Measure

Jack the vehicle and secure it on jack stands. Locate a straight section of exhaust pipe at least 12 inches long where the cutout will fit. Measure the outer diameter of the pipe to confirm you order the correct cutout size (typically 2.25 in, 2.5 in, 3 in, or 3.5 in). If you have a custom exhaust, the pipe diameter might differ from stock. Mark the cut location on the pipe with a felt-tip pen or scribe. Ensure there is enough clearance around the pipe for the cutout’s motor or actuator won’t hit the floorpan, frame, driveshaft, or suspension components.

2. Cut the Pipe

Use a reciprocating saw with a metal-cutting blade or a hacksaw to make a clean, square cut. A pipe cutter designed for exhaust tube can produce a cleaner cut but may be harder to use in tight spaces. Deburr the cut edges with a file or sandpaper. The length of the removed section should match the length of the cutout body (most are 4–6 inches). If you are using a clamp-on style cutout, you can cut only a small slit for a band clamp, but flanged cutouts require removing a section.

3. Prep the Pipe Ends

Clean the outside of the pipe ends where the cutout will attach. If using slip-fit connections, apply a thin layer of high-temp anti-seize to the pipe to prevent seizing and ease future disassembly. For flanged connections, ensure the flanges on the cutout match the pipe diameter and the bolt holes align. You may need to use a reducer or expander if the pipe diameter is different from the cutout.

4. Install the Cutout Valve

Slide the included gaskets onto the pipe ends and then position the cutout. Use the supplied hardware (bolts, nuts, springs) to sandwich the flanges together. Tighten the bolts evenly in a crisscross pattern to avoid distorting the flange. If using band clamps, tighten them to the manufacturer’s torque specification—do not overtighten, as this can warp the cutout housing. For manual cutouts with a cable, route the cable through a grommet in the floor and connect to the valve lever smoothly with no kinks.

5. Electrical Installation (Electronic Cutouts)

Disconnect the battery. Mount the switch in your chosen location (e.g., a blank switch plate, the center console, or under the steering column). Route a fused 12V wire from the battery or a constant power source to the switch. Then run a wire from the switch to the cutout motor’s power wire. Ground the motor with a short wire attached to a clean chassis ground point. Some systems require two wires for direction reversal: one for open, one for close. You will need a DPDT momentary toggle or a dedicated control module. Follow the wiring diagram included with your specific kit. Insulate all connections with heat shrink and use grommets or split loom wherever wires pass through metal holes.

6. Check for Leaks and Clearance

Reconnect the battery, start the engine, and let it idle. Place a hand or a piece of cardboard near each joint to feel for exhaust pulses. Spray a soapy water solution (50/50 water/soap) around all connections; bubbles indicate leaks. Tighten clamps or bolts as needed. While the car is still on jack stands, have a helper operate the cutout while you check that the motor or cable moves the valve through its full range of motion without binding. Also verify the valve doesn’t contact any part of the car when open or closed. Lower the vehicle.

7. Test Drive

Take a short test drive with the cutout closed to ensure there are no new rattles or noises. Then open the cutout gradually (if using a variable controller) or fully. Note any changes in power delivery, drone, or unusual vibrations. If the car feels laggy or the check engine light comes on, there may be a leak or valve issue. Some vehicles (especially turbos) may require a boost controller recalibration after opening a pre-turbo cutout. Return to the shop and re-inspect after a heat cycle.

Performance Gains and Logging

Measurable horsepower gains from a cutout depend on how restrictive the stock exhaust is. On a typical mid-sized V8, opening a pre-muffler cutout can free up 5–15 horsepower at the wheels. On a turbocharged four-cylinder, the gains are often even more pronounced because reducing backpressure allows the turbo to spool more quickly. However, gains are marginal on very free-flowing aftermarket exhausts. The loudness increase is always dramatic: expect a 10–20 dB jump, which is enough to draw attention.

Be aware of the downsides: long-term use with the cutout open in a daily driver can lead to exhaust heat damage to nearby components (brake lines, ABS sensors, wiring) and may cause interior drone at specific RPM ranges. Some drivers also report decreased fuel economy when driving with the cutout open because they unconsciously drive harder to enjoy the sound.

Exhaust cutouts exist in a legal gray area in many regions. In the United States, federal law prohibits any modification that removes or renders inoperative emissions control devices (catalytic converters, mufflers) on vehicles driven on public roads. Many states, including California, New York, and Texas, have specific noise ordinances that prohibit operation of vehicles with modified exhaust systems that exceed certain decibel limits. A cutout that allows bypassing the muffler can be cited as an illegal modification even when closed, because it is a tampering device. In Europe, similar rules apply under EU regulations. Always check your local laws before purchasing and installing a cutout system. If you have emissions testing, you will need to ensure the cutout does not trigger a check engine light. For off-road and track use, cutouts are generally unrestricted.

Maintenance and Longevity

Exhaust cutouts operate in a harsh environment. Regularly inspect the valve and actuator for corrosion, seized bolts, and exhaust leaks. Apply anti-seize to the butterfly shaft once a year if rust becomes an issue. For electronic cutouts, ensure the motor wiring and connectors stay clean and dry. If the valve starts to stick or moves slowly, the motor may be failing, or the shaft might have carbon buildup. Some high-end cutouts have rebuildable motors and replaceable seals. If you live in a salt-belt region, wash the underside of the car in winter to remove road salt that accelerates corrosion. Plan on replacing the gaskets every 2–3 years as part of regular maintenance.

Alternative: Cutout With a Controller

For maximum convenience and flexibility, pair your electronic cutout with a dedicated controller module. These controllers allow you to set cutout position based on RPM, throttle position, or gear. For example, you can program the cutout to open automatically above 3500 RPM and close below. This gives you the best of both worlds: quiet cruising and a roaring high-RPM experience without having to flip a switch manually. Some controllers also include a valet mode that locks the cutout closed to prevent unauthorized use. Expect to pay $150–$250 for a quality controller, but the integration is well worth it for tech-savvy builders.

Final Recommendations

Before you start cutting into your exhaust, decide what percentage of your driving will be done with the cutout open. If it’s occasional use (track days, car meets), a quality electronic cutout from a reputable brand like QTP, DMH Performance, or Vibrant Performance will serve you well. For a pure track car, a manual cutout saves money and weight. Always use stainless steel hardware, double-check clearances, and seal every joint thoroughly. And never forget: an exhaust cutout is a tool for enjoyment, not a permanent part of the car’s operating system. Use it responsibly to avoid tickets, neighbor complaints, and unnecessary wear on the engine.