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I know the reasons why old cars backfire, but I've noticed that new fuel injected supercars do this as well in the video game Driveclub. I know a video game doesn't seem like a reliable source, but I researched and found that the game creators simulate each car and the in-game driving experience very closely to their real life counterparts, even claiming they recorded the engine sounds of every car in real life to make sure that the in-game car audio reflects the sounds of the actual engine.

That given, I noticed that lots of the supercars/hypercars backfire a lot. Sometimes this happens during acceleration, but never during pure linear acceleration, mostly when coming out of a turn. This is usually indicated by somewhat subtle flames coming out of the exhaust and sometimes a soft popping noise. More prominently however, I've noticed it during deceleration, making two loud pops in quick succession accompanied by two quick bursts of intense flames shooting out the exhaust.

I've researched this online myself but I haven't found a complete explanation. I have also seen some explanations as why this happens in drag racing cars, but I wouldn't suspect the same explanation would hold for street legal cars since they are constructed and purposed differently. So, why do supercars backfire during acceleration, but not during linear acceleration? And why is the backfiring so much different during deceleration (specifically the two pops, louder noise, and bigger fire)?

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While fuel injected cars have the ability to cut off fuel when the throttle is closed they don't have to and this could happen either as a deliberate decision in designing the engine map or as a side effect of something else and while digital ECUs can respond very quickly they still aren't instantaneous an in a high revving engine an ignition cycle happens very quickly indeed.

One thing which can cause this is if the engine mapping deliberately introduces fuel into the cylinders even when the throttle is closed. One reason to do this is to maintain a high velocity exhaust gas flow to maintain turbo speed or because the exhaust gasses are being used for some aerodynamic function as in a blown diffuser.

Also high pressure turbos can make a variety of noises either from the dump valve or flutter when the turbine stalls under high boost or closed throttle. turbocharged engines may also prefer to run rich at high boost pressures to mitigate knocking.

Another possibility is the rev limiter, these can limit revs either by reducing fuel input or cutting the ignition if the latter is the case then this can put unburnt fuel into the exhaust. This is less common in production cars as it is bad for emissions and can damage catalytic converters but may have advantages in racing where hitting the limiter is more normal. As well as a 'red line' limit variable rev limits may also be used as part of a traction control system especially form standing starts or pulling away from a corner which tend to be traction limited situations. Some systems may even cut the ignition to some but not all cylinders to control torque in traction limited situations.

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Ryan - "Backfires" are the result of non-combusted fuel vapors making their way into a hot muffler. The pops you describe in your post are DOWNSHIFTS, moments when the transmission is being shifted into a lower gear, producing a higher torque gear ratio, but also sending the engine RPMs abruptly upward. The onboard system then reacts by increasing the duty cycle of the fuel injectors to direct pressurized flow into the combustion chambers.

Each car is different in its precise system configuration but generally all modern supercars operate Drive-By-Wire (DBW), which means the driver's throttle input is mediated by a computer module, as opposed to earlier technology where a mechanical connection attached the footpedal to the throttle plate to force it open commensurate with pedal travel. You may notice that older muscle cars and hot rods are less likely to exhibit the characteristic backfire in question.

This is because modern supercars are highly tuned to maintain "stoichiometric" Air to Fuel ratio. This is of course very difficult on a car that produces high peak power at low RPM and is intended to be driven "spiritedly".

When the system is supplied more fuel than it needs, it is called RICH. When the system is supplied less fuel than it needs, it is called LEAN. A lean air/fuel mixture burns at a higher temperature than a rich one, so running LEAN can lead to accelerated thermal wear and component failure. Therefore, since the A/F ratio is fluctuating with driver input, manufacturers err on the side of caution and set their fuel maps with a tendency to run rich. That is why supercars all backfire wildly.

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