Narrator: We've all seen it,
whether in movies,
at car shows and race tracks,
or from the Lamborghini passing you on the highway
flexing its wildly loud V12 engine —
flames bursting from a tailpipe.
It's exciting, loud, and sometimes even scary.
This phenomenon known as afterfire doesn't happen
to your average car.
In a combustion engine, vaporized fuel and oxygen
are mixed together and ignited.
These contained explosions drive the engine to rotate
and get the wheels spinning.
But sometimes, not all of that fuel gets burned up.
If the fuel travels into the hot exhaust pipes
and gets the chance to meet the oxygen outside,
it ignites in a burst of fire
when it comes out of the tailpipe.
This doesn't happen in your typical front-engine
passenger car.
Their engines are smaller and low-powered,
requiring far less fuel to function.
They also have more extensive exhaust systems
for the fuel to travel through before reaching the tailpipe,
making it harder for them to get hot enough
to cause afterfire.
And their exhausts feature catalytic converters,
devices that clean up pollutants like
excess fuel vapor to make for cleaner emissions.
But a Lamborghini with a 12-cylinder engine
at the back of the car only needs a short exhaust
that's piping hot from emitting 760 horsepower
worth of combustion gases.
Its catalytic converter barely has a chance to be effective
before the extra fuel ignites.
However, those bursts of flames are just as possible
with smaller, turbocharged engines,
particularly ones with anti-lag systems.
Found on race cars and tuner cars,
anti-lag is a system designed to overcome
the acceleration limits of turbochargers.
Turbochargers give cars an extra boost
by sucking compressed air into the engine.
Everyone knows fire requires oxygen.
So this makes for better combustion
and a more powerful engine.
Turbochargers are driven by the car's exhaust gases.
These gases wind a turbine connected to an impeller
that begins to draw in air.
Taking your foot off the throttle
causes the exhaust gases
to halt and your turbocharger to stop spinning.
Once you put your foot back on the throttle,
that extra time it takes to get the turbo back into
boost mode is known as lag.
Anti-lag involves programming your engine
to create a delayed, smaller ignition.
The delayed spark not only allows more fuel
to enter the cylinders,
but causes combustion to occur as late as possible.
This fuel-heavy mixture continues igniting
outside the cylinder
and into the exhaust manifold,
where the turbine is.
The heat of the exhaust causes it
to keep combusting
and spooling up the turbine
so your engine receives a constant boost.
The flames from that combustion
outside the engine
come out of your tailpipe.
A third source of exhaust flames
are two-step rev limiters.
You may know them on consumer cars
as launch control systems.
Essentially, the car's programmed to limit how fast
the engine spins to maximize acceleration
while preventing you from blowing out your engine.
With the first rev limiter,
the computer tells the engine to hold at a certain RPM
that it thinks is best for launch.
This is designed to minimize your wheels
from spinning too much, give your tires
as much grip as possible, and get you moving down the road
quickly from a stop.
The second rev limiter sits near the engine's redline,
the maximum engine speed
that an internal combustion engine
is designed to operate without causing damage
to internal parts.
Due to safety and emissions laws,
factory launch control systems
limit the engine's RPM
by adjusting the air-fuel mixture to be leaner on fuel.
But aftermarket solutions simply
delay or cut its ignition.
But where does the unburned fuel go?
You guessed it.
If you're thinking about modifying your car
so it spits fire, beware.
In most states, vehicles that have been modded
to shoot flames can result in a ticket on public roads.
Unless your big engine supercar can't help it,
remember that flaming exhausts are best reserved
for car shows, meet and greets, and the race tracks.