Exhaust Flamethrowers: Do They Work on EFI Cars?

When it comes to making a statement with your vehicle, few modifications are as dramatic and controversial as an exhaust flamethrower. The sheer spectacle of flames erupting from the tailpipe captures attention like little else. But beyond the visual appeal, a common question arises: can these fiery enhancements actually work on modern, fuel-injected vehicles, or are they strictly for older, carburetted classics? This article delves into the mechanics of exhaust flamethrowers, explores the distinctions between DIY setups and professional kits, and crucially, addresses their compatibility with fuel-injected (EFI) systems, all while emphasising the paramount importance of safety.

The Fiery Mechanics: How Exhaust Flamethrowers Ignite

At its core, an exhaust flamethrower operates on a simple principle: igniting unburnt fuel in the exhaust system. Your engine is designed to burn fuel efficiently, but sometimes, a small amount of fuel can pass through the combustion chamber unburnt, especially under specific conditions like revving and then suddenly cutting the ignition. This unburnt fuel then travels down the exhaust pipe.

To create flames, a flamethrower system introduces two key elements into the exhaust stream: more unburnt fuel and a spark. The system momentarily interrupts the vehicle's ignition, forcing a greater quantity of unburnt fuel into the exhaust. Simultaneously, a dedicated spark plug, strategically placed within the exhaust pipe, ignites this fuel, creating the spectacular flame.

The DIY Approach: A Detailed Look and Its Limitations

For the mechanically inclined, the idea of building an exhaust flamethrower at home can be tempting. The process involves creating a 'control box' and integrating it with your vehicle's electrical and exhaust systems. However, it's vital to understand the significant limitations of this method, particularly concerning modern vehicles.

Essential Components for a DIY Flamethrower:

To construct a basic DIY flamethrower, you'll typically require the following parts:

• One (1) SPDT Relay (Single Pole Double Throw Relay): This electromagnetic switch is the heart of your control box, managing the electrical signals. It has a coil (terminals 85 & 86), a common terminal (30), a normally closed terminal (87a), and a normally open terminal (87).
• Two (2) Ignition Coils: These produce the high voltage necessary to generate a strong spark, igniting the unburnt exhaust gases.
• Two (2) Coil Wires: Approximately 36 inches or longer, these connect your coils to the spark plugs.
• Two (2) Spark Plugs: Long shank, deep plug designs are preferred to ensure the spark reaches effectively into the exhaust tube.
• Two (2) Spark Plug Bungs: These are metal fittings that are welded into your exhaust pipe, providing a secure and sealed mount for the spark plugs.
• One (1) Momentary Switch: A push-button or toggle switch that only completes a circuit while pressed, similar to a car's starter button.
• Five (5) Terminal Connectors: For securing wires to relay terminals.
• Ten (10) Wire Connectors: For various electrical connections.
• One (1) Project Box: To house and protect the relay and wiring for the control unit.
• One (1) 1/2″ Rubber Grommet: To protect wires passing through the project box.
• 14 Gauge Electrical Wire: In various colours (Green, Blue, Black, Red, Yellow) for clear wiring identification.

Building the DIY Control Box: Step-by-Step

The control box is where the electrical magic happens. Here's how to assemble it:

1. Cut five 12-inch lengths of each coloured wire (Green, Yellow, Black, Red, Blue).
2. Crimp terminal connectors onto one end of each of these five wires.
3. Connect the GREEN wire to terminal #87A on the relay.
4. Connect the YELLOW wire to terminal #87 on the relay.
5. Connect the BLACK wire to terminal #86 on the relay.
6. Connect the RED wire to terminal #85 on the relay.
7. Connect the BLUE wire to terminal #30 on the relay.
8. Drill a 1/2-inch hole into one end of your project box and insert the rubber grommet.
9. Feed the unconnected ends of the five wires through the grommet and secure the box top.
10. Attach a wire connector to each of the five wires that extend from the box.

Installing the DIY Flamethrower Exhaust System:

Once your control box is ready, the installation moves to the vehicle itself:

1. Find a secure location for the Control Box within your vehicle, such as under the dashboard or on the firewall.
2. Locate your vehicle's existing ignition coil. Connect a wire from the negative terminal of your vehicle's coil to the GREEN wire from your Control Box.
3. Disconnect the wire that was originally connected to your vehicle's coil negative terminal and connect it instead to the BLUE wire from your Control Box.
4. Find an ignition wire that receives power when the ignition is on. Connect the RED wire from your Control Box to this wire.
5. Mount your Momentary Switch. Connect one terminal of the switch to a vehicle ground. Connect the other terminal to the BLACK wire from your Control Box.
6. Mount the new ignition coil(s) securely on your vehicle's frame rail or other suitable location.
7. Drill a hole approximately six inches behind your exhaust or muffler for the spark plug bung. Weld the bung into place.
8. Run a wire from your car battery's positive terminal to the positive terminal of each newly mounted ignition coil.
9. Run a wire from the negative side of each new ignition coil to the YELLOW wire from your Control Box.

Once installed, start your vehicle, keep it in Park (or neutral), rev the engine, and press and hold the switch. The engine should begin to stall, and if all is correct, flames should erupt from your exhaust.

DIY Flamethrower: Critical Compatibility Warnings

This DIY method comes with significant caveats:

• Catalytic Converters: This setup will not work on vehicles equipped with catalytic converters. The converter is designed to burn off unburnt fuel and emissions, preventing the accumulation needed for flames and potentially damaging the converter itself.
• Fuel-Injected Vehicles (EFI): Crucially, this specific DIY method is generally stated as not working effectively with fuel-injected vehicles. It works best with vehicles equipped with a manual choke and is typically assumed for a dual exhaust setup. The precise control over fuel delivery in modern EFI systems makes it difficult to generate the necessary unburnt fuel in the exhaust using this simple ignition interruption technique.

Professional Flamethrower Kits: The EFI Solution

While the DIY approach has severe limitations for modern cars, professional-grade exhaust flamethrower kits offer a more refined and compatible solution, particularly for fuel-injected vehicles. Companies like Hot Licks Exhaust Flamethrower kits provide complete systems designed to overcome the challenges faced by DIY builders.

How Professional Kits Address EFI Compatibility:

Unlike the basic DIY method, professional kits utilise advanced solid-state electronic circuitry and dedicated control modules. These modules are engineered to momentarily interrupt the vehicle's ignition system in a controlled manner that is compatible with EFI systems, ensuring that sufficient unburnt fuel reaches the exhaust without causing significant issues for the engine's sophisticated electronics.

• Stock EFI Applications: These kits can produce impressive 6-12 inch blowtorch flames on standard fuel-injected vehicles.
• Performance EFI Applications: Vehicles with performance-tuned EFI systems can achieve even larger flames, typically 12-24 inches.
• Naturally-Aspirated / Carburetted Applications: These older systems can also produce substantial flames, generally in the 12-24 inch range with professional kits.

It is important to note, however, that even professional kits will not produce any flames on applications with a catalytic converter, for the same reasons as the DIY method.

Features and Inclusions of a Professional Kit (e.g., Hot Licks):

Professional kits are designed for ease of installation and reliability:

• 100% Complete: Everything you need is included, from control modules to spark plugs and wiring.
• Waterproof Flame Control Modules: Built-in spark plug cables for durability.
• CNC Machined Spark Plug Bung Nuts: For precise and easy installation.
• Super-Hot Spark Plugs: Optimised for exhaust ignition.
• Water-Resistant Spark Plug Boots: Protecting the electrical connections.
• Special 3-Way Momentary Push Button: For activating flames.
• Nylon Electrical Connectors & Primary Wire: For secure wiring.
• Detailed Step-by-Step Installation Instructions: To guide the user.
• Lifetime Warranty: A significant advantage over homemade setups, reflecting confidence in the product's durability.
• Tech Support: Access to live person support for installation queries.

For those seeking even more dramatic effects, some kits offer 'Mega Flames Plans' which guide users through purchasing and installing additional components to create flames exceeding 2 meters in length.

Other Flamethrower Alternatives and Considerations

Beyond the direct flamethrower kits, other concepts can lead to flames from an exhaust, often associated with performance modifications:

• Stand-Alone Ignition Systems: As demonstrated by experts like Karl Fisher from Make It Kustom, it's possible to build a dedicated stand-alone ignition system specifically for exhaust flamethrowers. This typically involves components such as toggle switches, 5-pin 30 amp relays, in-line fuse holders, ignition condensers, ballast resistors, ignition coils, spark plugs, and spark plug wires, along with weld-in nuts for the pipes. This approach offers more control and can be tailored for specific applications.
• Anti-Lag Systems: While not primarily flamethrowers, anti-lag systems found in high-performance, turbocharged vehicles (like some Mitsubishi Evos or Subarus) often produce flames. This is a side effect of injecting fuel into the exhaust manifold to keep the turbo spooled up during gear changes or off-throttle situations. This is a complex engine management modification, not a simple exhaust accessory, and is designed for performance, not just show.

Safety, Legality, and Responsibility: Non-Negotiable Aspects

Regardless of whether you choose a DIY build or a professional kit, it cannot be stressed enough that exhaust flamethrowers are inherently dangerous and come with significant risks. The heat generated by these flames can be extreme, posing a serious fire hazard to anything or anyone nearby. Furthermore, unintended backfires or malfunctions could potentially damage your vehicle's exhaust system, or even engine components.

Crucially, these kits are intended for track and off-road use only. Using an exhaust flamethrower on public roads is illegal in most, if not all, jurisdictions due to the extreme danger it poses to pedestrians, other vehicles, and property. Professional installation is highly recommended to ensure safety and proper functionality, mitigating risks as much as possible.

You, as the vehicle owner, accept all responsibility for the installation and use of such a system. Always exercise extreme caution and be aware of your surroundings.

Comparative Analysis: DIY vs. Professional Kit

Understanding the differences between building your own flamethrower and purchasing a complete kit is crucial for making an informed decision.

Frequently Asked Questions (FAQs) About Exhaust Flamethrowers

Are exhaust flamethrowers legal on public roads in the UK?

No, exhaust flamethrowers are generally not legal for use on public roads in the UK or most other countries. They are considered an extreme hazard due to the risk of fire and injury to others. Their use is strictly limited to off-road, track, or private property environments where safety precautions can be fully controlled.

Will an exhaust flamethrower damage my engine or exhaust system?

If installed incorrectly or used excessively, an exhaust flamethrower can potentially cause damage. The extreme heat can stress exhaust components, and improper interruption of the ignition system could lead to engine issues. Professional kits are designed to minimise these risks, but caution and adherence to instructions are always necessary. Systems that do not require welding the spark plug bungs into the exhaust are generally safer for the exhaust system itself, though the heat from the flame remains a concern.

Can I install a flamethrower on a car with a catalytic converter?

No, exhaust flamethrower systems, both DIY and professional kits, will not work on vehicles equipped with catalytic converters. The catalytic converter is designed to burn off unburnt fuel and emissions, preventing the necessary build-up of fuel in the exhaust for flames. Attempting to use a flamethrower on a car with a catalytic converter will not only fail to produce flames but could also severely damage or destroy the converter, which is an expensive component to replace.

What's the difference between an exhaust flamethrower and an anti-lag system?

While both can produce flames, their primary functions are entirely different. An exhaust flamethrower is a modification purely for visual effect, designed to ignite unburnt fuel in the exhaust for a show. An anti-lag system, on the other hand, is a performance modification for turbocharged engines. It injects fuel into the exhaust manifold to ignite and keep the turbocharger spooled up when the driver lifts off the accelerator, reducing turbo lag. Flames from an anti-lag system are a byproduct of its performance function, not its main purpose.

How big will the flames from an exhaust flamethrower be?

The size of the flames varies significantly depending on the system, vehicle type, and engine modifications. For professional kits, stock EFI applications might produce 6-12 inch flames, while performance EFI and carburetted applications can achieve 12-24 inch flames. Some advanced setups with additional components can even produce flames over 2 metres. DIY setups are less predictable and often produce smaller, less consistent flames, if any, especially on incompatible vehicles.

Final Thoughts: Igniting Responsibly

Exhaust flamethrowers are undeniably spectacular, offering an unparalleled way to make a vehicle stand out. While the DIY approach presents significant hurdles and is largely incompatible with modern fuel-injected vehicles, professional kits have evolved to safely and effectively produce flames from EFI systems, provided the vehicle does not have a catalytic converter. However, the allure of the flame must always be balanced with a deep understanding of the inherent risks and responsibilities. Remember, these are highly specialised modifications strictly for off-road or track use. Prioritise safety, understand the limitations of your vehicle, and always consider professional guidance before attempting to turn your exhaust into a fire-breathing spectacle.

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