# Fire out the exhaust pipe... **URL:** \ **Category:** Factual Questions\ **Created:** [June 26, 2002, 6:02am UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987 "2002-06-26T06:02:51Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![DJMgt](https://avatars.discourse-cdn.com/v4/letter/d/958977/32.png) [@DJMgt](https://boards.straightdope.com/u/DJMgt)\ **Post date:** [June 26, 2002, 6:02am UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/1 "2002-06-26T06:02:51Z")
I’ve always wondered why fire would come out the exhaust pipe on some very powerful cars/beefed hot rods. Can anyone explain why this happens/how people make it shoot fire? ---
**Author:** ![Berkut](https://avatars.discourse-cdn.com/v4/letter/b/a88e57/32.png) [@Berkut](https://boards.straightdope.com/u/Berkut)\ **Post date:** [June 26, 2002, 6:10am UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/2 "2002-06-26T06:10:11Z")
Lot of it has to with aggressive valve timing. The exhaust valves are timed to open a little earlier, and the gasses are still burning when leaving the cylinder. Also, some cars have an overly rich air/fuel mixture for cooling, and this extra fuel can ignite in the pipe. ---
**Author:** ![Rocketeer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rocketeer/32/4437_2.png) [@Rocketeer](https://boards.straightdope.com/u/Rocketeer)\ **Post date:** [June 26, 2002, 1:33pm UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/3 "2002-06-26T13:33:48Z")
On custom cars, you rig up spark plugs in your exhaust tips with a coil to fire them when you push a button. Run the engine fast, close the choke. This gets raw gas coming out your exhaust. Fire the plugs=flames. On dragsters, I’ve heard that it’s hydrogen burning, since the tremendous temperatures dissociate water molecules in the exhaust. Hmmmm. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [June 26, 2002, 2:36pm UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/4 "2002-06-26T14:36:32Z")
> [@](#): > > \*Originally posted by Rocketeer \* > \*\* > On dragsters, I’ve heard that it’s hydrogen burning, since the tremendous temperatures dissociate water molecules in the exhaust. Hmmmm. \*\* I seem to remember reading somewhere that hydrogen burns with a flame that is not visible in daylight. Sorry, no cite. But, if correct, it would seem that the flames are probably not from hydrogen. Unburned fuel is more likely. And would the sparkplug trick work with modern vehicles? ---
**Author:** ![handy](https://avatars.discourse-cdn.com/v4/letter/h/b5a626/32.png) [@handy](https://boards.straightdope.com/u/handy)\ **Post date:** [June 26, 2002, 2:43pm UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/5 "2002-06-26T14:43:39Z")
“And would the sparkplug trick work with modern vehicles?” Well, seems most vehicles doing it are modern. What happens to the car in back of ya? ---
**Author:** ![Belrix](https://avatars.discourse-cdn.com/v4/letter/b/ed655f/32.png) [@Belrix](https://boards.straightdope.com/u/Belrix)\ **Post date:** [June 26, 2002, 3:33pm UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/6 "2002-06-26T15:33:45Z")
The “Monster Garage” show on discovery showed that they had a propane feed into the tailpipe in front of the spark plug to help make the flames out the pipes. So for street rods, this flames might be fakes… ---
**Author:** ![dead0man](https://avatars.discourse-cdn.com/v4/letter/d/edb3f5/32.png) [@dead0man](https://boards.straightdope.com/u/dead0man)\ **Post date:** [June 26, 2002, 7:18pm UTC](https://boards.straightdope.com/t/fire-out-the-exhaust-pipe/115987/7 "2002-06-26T19:18:05Z")
Racing RX-7’s (or any rotary) are notorious for this. Any rotary in poor health has the ability to do it as well. During hard acceleration there is a lot of fuel pumped into the motor. When you lift off to shift, there is some fuel that gets through the rotary unburned and when it gets to the very hot headers,(rotary exhausts are quiet a bit hotter than a piston) it explodes causing fire out the back. My 2nd RX-7 did this and you could see it pretty good at night. Coming out of the back of that POS it was more pathetic than cool though. dead0man