Why do some supercars have flaming exhausts when changing gears?

Question

Have you got one of those (standard, with no modify)? What car is it?

Answer 1

You are probably aware that cars have four stroke motors...the four strokes being intake, compression, power, and exhaust. What you may not realize is that these strokes don't exactly correspond to the opening and closing of valves. More specifically, the intake valve opens somewhat before the exhast stroke is finished, while the exhaust valve is still open. The main reason this is done is because the intake charge has forward momentum, and tends to push exhaust gas out of the cylinder. This is called scavenging.

One way that you can "soup up" a motor (any motor) is to increase the amount of valve overlap...meaning that there is more time that the intake and exhaust valve are simultaneously open. This is done by swapping to a cam with a longer duration. This was common practice in the muscle car era. Modern cars still do this, although some have variable valve timing, which accomplishes the same thing by varying lobe centers.

At high engine speeds there is little time to scavenge the cylinder. A long duration cam makes more horsepower at high RPM, because it increases scavenge time. But the consequence of this is that at lower RPMs, fresh intake mixture can end up flowing directly out the exhaust port. In the case you describe, when the driver lifts to change gears, the RPM's momentarily drop, allowing unburned mixture to be drawn out the exhaust port. The mixture then burns in the exhaust system, and that's what you see.

Answer 2

Many supercars are chipped to provide an exceptionally rich fuel mixture. During a shift (usually a downshift) unburned fuel is being dumped directly into the exhaust port where it combusts inside the hot exhaust manifold and blows out the exhaust tip.

Answer 3

Incredibly poor air/fuel control!

More specifically, they probably disable fuel injection to reduce torque to soften the blow of a gear shift. But there is some fuel stored on the intake port walls, especially on a cold engine. This fuel enters the combustion chamber during intake but does not burn in the cylinder because the regular fuel injection was turned off so the mixture is too lean. The unburned fuel progresses to the exhaust and there combusts. Now there would generally not be a visible flame unless the catalytic converter was removed, which is a good bet.

Answer 4

unburnt gas exiting the hot exhaust ,usually when slowing down

Answer 5

i dont know...why do some cars that men think are super have exhausts as big as the car?

Answer 6

you can buy flame kits but they are illegal

Answer 7

nitrous or flame kit