Exhaust Flame Throwers


Here’s a hack that’s been around since the very start of the hot rod movement. Car exhaust flame throwers work by interrupting the spark to the engine. This dumps raw fuel into the exhaust system. The fuel is ignited by a coil and spark plug placed right before the exhaust tip. Doing this will shorten the life of your engine (and pedestrians). The raw fuel strips the oil off the cylinder walls and contaminates the oil causing more wear and tear. Also, this mod can’t be used on a fuel injected car. It would foul the O2 sensors and catalytic converter. Never the less, our fascination with electricity will live on.

[thanks matticus66]

50 thoughts on “Exhaust Flame Throwers

  1. Yeah, a friend did this using a 510cc injector off the fuel return line i beleive, he controled the injector and sparkplug with some switched in the car. He controlled the pulse width to the injector with something… I’m no good at that stuff so I’m not sure…

  2. The article states that the hack/mod does not work for fuel-injected or electronic fuel-injected (same smell right?) vehicles. But on the contrary… with a catless exhaust system and a richer air/fuel mix, the exhaust gasses can be reignited. Granted of course the flames are more like quick bursts of smoke most of the time (with an occasional flame here and there), but nonetheless… an exhaust “popping” sound. This mod seams to be a little more high-tech as compared to just purchasing a blast coil and a spark plug and some wires. Great mod!

  3. yeah miller, I’ve seen it with propane too
    Usually those kickass ones at car shows

    best looking one I’ve gotten to look at closely used a slick little side by side exhaust setup, piped exhaust out one and would fill the other with propane from a tank in the trunk, then vent exhaust through the propane filled one while sparking the igniter, it was fairly ingenious, albiet a little complex comparatively, but the effect looked outstanding, nice solid flame, almost like a welding torch in shape

    simplest was a brass nipple through the pipe, connected to a solenoid off a propane generator, connected to a highflow regulator on a standard tank, shorter flame, but it was cheap to make, cheap to upkeep, and with the concept of “what isn’t there can’t break” should last as long as the solenoid and/or coil

  4. you don’t need to cut the spark to the engine to make it work. If the engine is left just a touch on the rich side the exhaust gases can be reignited. This goes for carbed engines. Also an engine always goes to the rich end during acceleration and deceleration. mash the throttle and let off. During both the uptake and downside the engine is rich by design thus giving the flames. the only time you wouldn’t have any is when it is just idling or while you are just cruisin down the road.

  5. yeah I have done a few things like this
    even with a efi system you can tune you
    idle to run rich you just need a multi meter to watch your O2 sensor then adjust your idle fuel
    or if you have a Mega squirt or any other
    standalone EFI computer can be programmed witha rich fuel map for just such fun things maybe I’ll
    when the new side dumps on my mud truck are done I’ll make a slightly rich map on my Mega Squirt and light it up get some nice side lighting not really for use while 4x4ing I wouldn’t want to light the forest on fire

  6. I love how he points out that it matters which direction you install the resistors. Is there such a thing as polarized resistors? Ha. I guess you learn something new every day…

  7. I did something similar, quite by accident, with my car. It seemed that one of the plugs wasn’t firing. So all that unspent fuel got dumped into the catalytic converter as I was driving. Which is where it ignited and caught fire.

    I was driving around town with a RED GLOWING HOT catalytic converter. When I parked it and discovered a strange smell, I was sure the car was going to blow.

    But nope. The red hot metal eventually cooled and everything was back to normal again. No explosion. No long term damage that I was aware of. (Except, perhaps, for less treatment of my exhaust.)

  8. VW bug exhaust hack:

    While going down the freeway, put in the clutch and turn off the ignition. Pump the gas pedal several times to make the accelerator pump in the carb pump in a bunch of extra gas- which flows through to the exhaust uncombusted. Turn the key back on and let the clutch out. Boom!

    Just make sure you budget for a new muffler.

  9. this mod is somewhat legal, provided that it does not produce excessive noise.

    the legal problems actually come when you add fuels to your exhaust pipes, probly wy he just didn’t take the easy route and use propane

  10. Couldn’t you connect a switch to the spark plug in the exhaust so it doesn do it all the time? My father-in-law did this back in the day, think he just ran a spark plug in the exhaust line for acc/deaccelaration lighting.

  11. This will also work in an EFI car. If the catalytic converter has been removed (replaced with a straight pipe or the like) and you place a spark plug in the exhaust tip or before it should ignite the unburned fuel…assuming you aren’t running too lean. Also, I have only seen this work on a turbocharged car, not that it should matter.

  12. I made one of these for diesel trucks. I used a propane system and a taser for ingnition (spark plugs foul with diesel smoke). I got 10 foot flames with the flow set on high. I will post pics when I get to my other computer.

  13. This mod actually CAN be done on a fuel injected car, but one would require a specially made kit (yes, they exist, and in quite large numbers, too!), or a bit of know-how and time to do it themselves. Either that, or a Mazda RX-7, a car which normally runs quite rich and has been known to spit flames from the exhaust regularly all by itself.

  14. i just built one and it seems that the power transmiters get hot and dont work again is this a common problem ive changed them but it keeps doing it ?
    but its getting good flames though when it works
    cheeers dave

  15. I haven’t done any mods to my car as of yet, but I am planning on using the ‘un-burned fuel’ type of flamethrower to get some results. If you wire a secondary ignition coil into your car somewhere (preferebly close to the tailpipe, I’ll explain why in a bit) and wire one terminal on that to the battery. Wire the other terminal to a switch, and wire the switch to a ground somewhere on your car (slip the wire under a bolt that touches the chassis, or something metal would usually work.) What this will do is produce a spark every time you throw the switch on, then off again. It works this way due to the nature of the coil. The spark comes out of the HV (High-Voltage) output on the coil, and arcs to the ground on the car (i.e., almost any metal on the car, tailpipe, chassis, engine, ya know). The coil ought to be close to the spark-plug because pulses of HV electricity don’t travel as far as 12 volt battery-style stuff. Any more questions, just post.

  16. i am going to install an electronic cold start fuel injector into my exhaust that is supplied right from my fuel rail. anybody know if this is a good idea? also where should the injector and spark plug be installed into the exhaust?

  17. Hello Mate!! first thanks for the DIY information!!!
    I built some and it seems that the power return to the transmiters and then don’t work again is this a common problem so I’ve changed them and include a diode but keeps doing it ? Could you please help me…
    Cheers Mate!!

  18. Hello Mate!! first thanks for the DIY information!!!
    I built some and it seems that the power return to the transmiters and then don’t work again is this a common problem so I’ve changed them and include a diode but keeps doing it ? Could you please help me…
    Cheers Mate!!

  19. You can create a fuel injected system using a nitros injector. Depending on your app. Its a simple design. You don’t have to run your engine rich and can be used as either gas or propane. I built and designed mulitple systems and all work great. I designed a modified tailpipe to allow for expansion ( flame ) instead of having the common torch flame. Anyone looking for info is free to e-mail me for plans. If I get enough responses I’ll create a link to the info. I even added nitros to the mix but I found out it was a ” little ” too much for how I had it installed. Blew the exhaust right off the headers! Still working on that. I was told the wire schematic didn’t work by some people. They said it got too hot but I have never had any problems. Take a look at it and redesign it if you feel its needed. Let me know. Drop me a line at aryan900@yahoo.com. Put flame under subject so I know its not spam. Laterz

  20. Hey, just hooked up an ignition coil and bolted it under my boot, connected that 2 the battery and earthd it, connected it to a spark plug in the exhaust tip and a switch in the dash. that works sweet. also put it switch in the dash which turns off all spark plugs in the engine, which should mean id pump raw fuel through my exhaust? spent a lot of time on this but cant seem to get any flames :S please help?

  21. Idea is right, circuit description has some mistakes though. This circuit could be improved upon a little bit. A rubber grommet is a MUST when running wires through a metal chassis. This mod as built does not interrupt the spark from the engine therefore the only fuel in the exhaust is what did not burn during combustion. If you wanted to interrupt the engine spark its easy with an MSD AL6, or AL6-2 select a low value for the 2step rev limit hit the rev limit swtic and rev the engine and it will randomly drop the spark from 1 cyl. The same cyl will never be dropped twice in row to prevent the washing of oil from the cyl walls. “raw unburnt fuel” (Sounds scary dont it?) is in you engine for 2 out of the 4 cycles anyway…

    Oh and to the guy who put a switch to the ignition coil and the battery, and rigged another switch to cut all the spark plugs. If your still alive… There is an infinite to list the reasons why you should put this project down.

  22. yeah igniting the fuel from all of the cylinders in the pipes at once doesnt sound like a good idea, I did however do the same thing with a switch for cutting the spark as more of an anti theft device, i have a hidden switch that cuts the power to the coil so that if someone were to bust the ignition, hotwire it etc. they could turn it over all they want and it wont start :) and as for the flames, it would work just to have plugs in the pipes and rev it up and let off it should ignite cuz the exhaust is always a little richer revving down, right?

  23. I did it in the 50’s using a Model T spark coil. It delivers a continuous spark. Basically it has a set of points that vibrate like a buzzer.

    To do the same thing with a normal ignition coil have an electronic hobbyist build a solid state multivibrator to power the coil. the transistors have to have enough front to back ratio to stand the back voltage from the coil. Or look for a Model T coil in an antique shop.

  24. hey yall. i’ve been wanting to hook a flamethrower in my car for a while now and i thought i had everything i needed. I got a small gas tank, fuel pump, nos nozzle, spark plug, coil, and switches. the plug fires when i press the momentary switch, but when i try to add the fuel injection it doesn’t work. I think its because the plug becomes covered in the gasoline i am spraying, and the air fuel ratio for combustion is off. any ideas? maybe a pump with less gph or higher psi?

  25. I am not sure what part the relay plays in the circuit. The base/emitter current to turn on the transistor is low as the main current flows through the emitter/collector circuit.

    The T-Model coil approach, which could easily be imitated with transistors, gives a continuous spark as long as the switch is closed so plug wetting or fouling become less of an issue.

    Does the illustrated circuit give one spark for one push of the momentary contact switch, or am I missing something?

  26. If you’re ever annoyed by people leaning against your ride try this; drop a trailing wire from one of the exhaust spark plugs to the ground. When someone leans against the car flip the switch momentarily and they will get a jolt.

  27. the easiest best way to do a flame thrower cheapest way works great with anything with points distributor,put 1 sparkglug in each exaushst bout a foot in,take a heavy wire, place it in 1 of the spark plug bongs in cap,run that to a toggle switch in dash from there run that other wire off switch to both spark plugs when u want flames let rev it few times,let off gas,hit the switch watch the flame richer carb is better flames, this is the actual 50s way.

  28. EFI or carb, ether way the best way to do this safely is a cheap micro electric fuel pump and a dry NOS sprayer mounted after the Cat. Bypassing the relaying the ignition and intentionaly causeing a misfire is vary hard on a engine. With the pump you can make it veriable in the amount of fuel injected into the line giving direct controll over the exhaust flames without screwing with your ECU or carb mixture or fouling up your pistons. Just drive the Coils with a 555, hell even a heavy duty relay setup to act as a buzz coil. If you want it alittle bit more complex use a MCU to monitor the transmission tach and time the fuel pump to pulse just befor the exhaust cycle release, ensureing little to no fuel is pulled by backpressure. As for propane, no that just screams rice right they always end up looking more like a blowtorch then a hotrod exhaust.

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  30. Ok all this would complex, for the spark in the pipes you only need two spark plugs and two coils put the plugs about12 to 18 inches in the pipes mount the coils where the plug wires can reach use long wires….. ok the you need a gm points distributor and a wiper motor take off the cam gear and hook up the wiper motor to the distributor then run power to a switch to run the motor then tap into the 12 volt power wire you ran to your wiper motor to the distributor then run two wires from the cap to the coils to shoot power to the plugs…that’s that then use a manual choke carb rev and choke ,what ever at all cost keep it running then hit the switch it will light and walla your flaming….injection is a oil different not good with that yet…

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