The familiar sound of a car backfiring is to some the most annoying sound you can hear on the road. For others, it’s the best sound a car can make. However, not all cars backfire, and some backfire for different reasons, which leaves many wondering why supercars in particular backfire.
Supercars backfire as a result of unburnt fuel exiting the engine through the exhaust system, where it then ignites and leaves the exhaust at high speed. This sometimes results in a visible flame leaving the exhaust, and is most often accompanied by a loud bang.
Below, we’ll take a closer look at what backfiring actually is and what causes it. We’ll discuss why some people want their car to backfire, and why you might not. We’ll then go through why supercars backfire, and which ones do, and which ones don’t.
What Is Backfiring?
Backfiring is the loud noise you’ll often hear supercars – and some normal road cars – make when they downshift or undergo heavy engine braking. The noise, and sometimes accompanying flame, is a result of unburnt fuel leaving the engine and passing through the extremely hot exhaust system, where it then ignites.
There is an ideal air to fuel ratio, somewhere around 14.7:1, at which an engine operates at its optimum level of performance. This ratio is managed by a carburetor in older cars, and a fuel injection system in modern cars. However, sometimes this ratio isn’t met, resulting in a lean or rich fuel mixture reaching the engine.
Lean And Rich
When the mixture is lean, the result can be a damaged engine, overheating, or engine knocking. However, when the mixture is rich, you’ll usually see lower gas mileage, poor acceleration and a strong smell of gas from your exhaust.
However, it’s only really if your fuel mixture is very rich or lean that you’ll exhibit these issues, as the air to fuel ratio is slightly different for different engines so there’s a bit of tolerance involved. But if the fuel mixture is rich enough, another side effect can be backfiring.
Essentially, the fuel mixture can be rich enough that there’s not enough air in the engine with the fuel at the time of ignition. When this is the case, the fuel cannot combust completely, which means some fuel is ejected along with the exhaust gases that result from normal, complete combustion.
This mixture of fuel and exhaust gases are then sent out through the exhaust system, which runs at a very high temperature. The ignition temperature – the temperature at which a substance will auto ignite without a spark – of gasoline is somewhere around 500oF, and exhaust systems can run at anywhere from a few hundred degrees to over 1000 if you’re driving long enough.
The Classic Sound
So, when the unburnt fuel reaches this exhaust system, not only does it meet oxygen contained in the air from outside the car, but it also reaches a high enough temperature to ignite without a spark. This results in a small but noticeable explosion, which can sometimes be accompanied by a visible flame, but is almost always an audible bang, sometimes a very loud one.
Having a rich fuel mixture isn’t the only cause of backfiring. So, why else might a supercar backfire?
Why Do Supercars Backfire?
Now that we know what causes the noise of a backfire, we need to understand what causes unburnt fuel to reach the exhaust in the first place. The obvious reason is a problem with the system regulating the air to fuel mixture that enters the engine. This can be the result of a problem with the carburetor or fuel injection system, or any number of faulty valves.
It could be the result of a timing issue, which could mean there’s a problem with the electronics of the car. Clogged filters, missing catalytic converters, and broken piping underneath the car can also lead to unwanted backfiring. But sometimes backfiring is the result of a system built into the car, and in some ways is a desired effect.
Backfiring By Design
As is the case with many supercars, backfiring often occurs when the driver shifts up a gear and takes their foot off the gas pedal. This leads to a moment of rich fuel mixture reaching the engine. This fuel mixture burns incompletely, and some fuel enters the exhaust system where it burns, causing a backfire.
This kind of backfire is a result of the parts of the car operating as they should, but a rich mixture making its way into the engine under a state of no acceleration. This usually means there won’t be any damage, but there’s still that iconic pop or bang as the fuel burns up in the exhaust.
Another common cause of backfiring in supercars that’s the result of a desired effect involves the anti-lag system. This is a system designed to keep the turbo spooled when the driver is off the throttle. When this happens, the pressure at the turbocharger drops, meaning it has to spin faster to result in the same level of power boost to the engine.
The anti-lag system overcomes this by allowing a small amount of fuel to escape through the exhaust system when the driver is off the throttle. This then combusts, for the reasons described above, and creates higher pressure at the turbocharger and keeps it spooled, reducing turbo lag.
F1 vs Road Car Engines
The final reason a supercar backfires is down to something we discussed in the previous section. The temperature at which an engine runs has a large effect on its lifespan. Take for example an F1 car’s engine. It can burn fuel at more than 4500oF, which, along with other wear and tear, leads to the engines lasting only a few thousand miles.
However, while the engine in your road car might burn fuel at temperatures close to that figure (albeit usually much lower) it never runs at that temperature for the same amount of time as an F1 car. An F1 car might run 300 km at an average speed well above 100 mph, while you’ll never achieve that in your road car.
This excessive heat leads to damage to the engine. Therefore, in high performance supercars, heat dissipation is an essential component of design. Running at the ideal stoichiometric ratio of around 14.7:1 can actually result in hotter running temperatures than if the engine runs a rich or lean fuel mixture.
This means supercar manufacturers often map the engine to run at a slightly rich fuel mixture, letting some of the fuel escape through the exhaust which leads to backfiring. This is a result of the rich fuel mixture making the engine run at slightly lower temperatures, therefore reducing engine wear, at the expense of manageable and controlled backfiring.
But aside from the reasons above, why would you want your supercar to backfire?
Why Would You Want Your Supercar To Backfire?
We’ve all heard the sound of a road car trying to sound like a racecar. It usually sounds loud and obnoxious, mainly because the noise often happens at speeds of less than 30 mph. This is hardly a racecar speed, yet some people still want their cars to make the iconic popping sound as they cruise through their neighborhood.
With a supercar, there is often a more pronounced pop or bang that sounds like it’s meant to be there, rather than being tagged on as a modification. The reason for that is that it is meant to be there in most cases, but to many petrol heads it also just sounds amazing. In the case where visible flames come out the exhaust, it can look amazing too.
Sound Is Key
Lots of people buy their supercars based at least partly on the sound it makes. If you’re buying a supercar to show off your wealth or even just because you value the power and precision engineering these cars have to offer, the extra bonus of excellent sound paired with incredible speed and agility makes it easier to hand over your money.
Many supercar owners want their car to sound like a supercar, so the classic backfiring sound is almost buying criteria for them. Classic examples of supercars that backfire include Ferraris and Lamborghinis, along with Aston Martins, Audi R8s and even Bugattis. But if you’re looking for luxury over raw performance, backfiring might not be a prerequisite for you.
Some Bentleys and Maserati’s may reach the speed and power of top end supercars, but most owners of these cars are looking for the luxurious feel and look of these cars, rather than the backfiring of their engines. Therefore, it all comes down to personal preference whether or not you do or don’t like the noise of a supercar backfiring.
Supercars backfire as a result of unburnt fuel leaving the engine through the exhaust system, before then igniting and creating the classic bang or pop sound. Aside from making the car sound aggressive, it also serves practical purposes in the case of high-performance supercars.