Thread: What causes the blue flames on the exotic cars ?

I noticed this on my friends car a few months back, and forced him in the car behind me while i showed him whats up....wish it were blue too though :-/

When decelerating throttle plate closes, which=less air, and also retards timing so less fuel as well. Combustion is slower at getting the burnt mixture out of the combustion chamber, so there are a few things that happen. Either they open the throttle plate a little bit, and exhaust valves so that air comes in, pushing the rest of the unburnt mixture out and starting the next cycle OR they add a lot more fuel because running rich is cooler than running lean. Combustion increases pressure inside the combustion chamber which expels the burnt mixture (after the air/fuel has been ignited by the sparkplug) faster than if you were to run lean (less fuel) which has a less powerful "explosion" (less fuel) which leads to less pressure and takes longer to expel hot gas=hotter conditions.

Especially on higher hp cars you will see the computer dumping fuel into the combustion chamber on decel. For instance slowing down to take a corner in a race car or slowing down on a dyno.

This can happen on daily drivers with decent amount of power and no cats running right off the header and really winding the engine up.

During accel, especially on cars with rear engine (small length of exhaust pipes before the rear of the car) its usually just more fuel because of the increase in the throttle from the driver. More fuel/more power/increase in rpms which means theres less time for burnt a/f mixture to leave the combustion chamber before the next combustion cycle. So you get fuel in the hot exhaust and bang.