someone on another local forum "Seth" expalned it REALLY well

alright.. there are a few reasons why flames will come out a tailpipe. These are refering to turbo'ed cars here...

first is the systems that the rally guys use its called An Anti Lag System or (ALS)
When the driver lifts his foot from the gas pedal the ignition timing is altered with sometimes 40° or more of delay (retard) and the intake air and fuel supply mixture is made richer. The inlet butterfly is kept slightly open or an air injector is used to maintain air supply to the engine. This results in air/fuel mixture that keeps getting in the combustion chambers when the driver no longer accelerates. The ignition being delayed, the air/fuel mixture reaches the exhaust tubes mostly unburned. When the spark plug fires, the exhaust valve is starting to open due to the ignition delay mentioned above. Additionally, the exhaust temperature being extremely high, the unburned fuel explodes at the contact of the exhaust tubes. Luckily the turbo sits right there and the explosion keeps it turning (otherwise it would slow down since its intake, the exhaust gases, is cut-off). The effect is vastly lower response times with some downsides...
1. Temperature of the turbo can go from 800°C to 1100°C+
2. huge stress on the exhaust manifold and pipes.. on a street car you can see your exhaust die in about 100 km
3. The turbo produces significant boost even at engine idle speeds
4. Reduced engine braking

usually flames and big bang noises happen out the exhaust.
The ALS effect is mostly dependent on the air allowed into the engine, the more air supplied the more the ALS effect will be noticeable. Consequently ALS systems can be more or less aggressive. A mild ALS will maintain a 0 to 0.3 bar pressure in the inlet manifold when activated whereas, when inactive, the pressure in the inlet manifold with the throttle closed would be in the region of -1 bar (absolute vacuum). Racing ALS versions can maintain a pressure of up to 1.5 bar in the inlet manifold with the throttle closed.
While the systems mounted in Toyota and Mitsubishi racing cars are relatively smooth and noiseless those fitted in Ford and Subaru cars are much more noisy and aggressive..

as for cars that do not have an als.. most of the time what happens is when people shift or people rev really high and let off the bov will throw all the air out of the system that the computer has already calculated the fuel mixutre for.. so the fuel goes in but no air.
the exhaust ignites the fuel and bang / flame.

Bee R has a rev limiter that works on the basis of ignition cut not fuel cut.
So in that case when drifting around a corner say.. one will have flames popping out and banging away because the unburnt fuel ignites in the exhaust.

keep in mind to see flames you can't have a cat.. unless you have blown it through.

 

Makes sense. I have herad about the anti lag system before. Just never figured out what it did before. Here is a nice video of Subaru ALS in action!

http://www.youtube.com/watch?v=WTAPpsL2xOU

 

haha, i was just about to post that^^ ya you can really hear it

 

Damn that car sound so mean, but all that popping i guess its ok.

 

That's it, I'm buyin a suby

 

hells yeah!

 

I'll take 2 please.. taht is awesome

 

Sounds like that car is going to need a valve job after the race. [:@] You know what they say...it takes $$ to go fast.

 

subarus are good for doing that, my buddies does it quite often, also, i too have seen other cars do it, like a toyota supra