Flames on over run

[Jon K]

So I am casually watching this video:

[youtube][/youtube]

And at 3:06 a porsche comes into view and is spewing flames constantly but its not flat shifting or ALS, its just flaming on over run. Why is this? They're obviously not running over run cut... why?

Again at 5:32 an Evo comes into frame, also spewing flames.

Are these guys keeping the fuel going for engine cooling or something? But hten, wouldn't fuel cut cool the most? I don't get why I see this from time to time with modern ECUs. It seems wasteful especially in a hill climb where you could prob get rid of a bit of fuel if you aren't busy setting it on fire @ the tail pipes lol

[Simon P.]

From my own experience so not necessarily the only possibility. As they say, your mileage may vary...
Both turbo cars. Probably running blow off valves plummed to vent to the atmosphere and placed between the AFM and the throttle plate. The BOV placement, the use of an AFM and the atmospere vent is the root cause here I think.
In high boost/WOT situations if the throttle closes quickly the extra boost vents through the BOV but the AFM doesn't know "where" that air went, it just knows it measured it and keeps telling the ECU to keep dumping WOT metered fuel, even though most of the air has bypassed the cylinders completly (out the BOV). This causes large amounts fuel to be dumped right into the cylinders and out the exhaust where it gets ignited by the hot exhaust heat and causes the cool looking exhaust flames. It also causes plug fouling and not so nice soot deposites around the tailpipe...
Obviously the situation corrects itself as soon as the blow off valve closes as the metered air now flows through the "correct" path rather than out the BOV.
I'm sure there are other reasons that could cause this like very long duration cams with quite a bit of overlap but the BOV thing is what's most common I think.
Used to happen to me (flames out the tailpipe) quite often with my turbo FC3S.
BTW very cool and fast cars in there... I espescially liked the open wheel and proto cars going at it! Nuts!!!

[stevieturbo]

I'd say camshaft and overlap are the biggest factors.

But basically you need fuel and more importantly air. ie. crack an idle valve fully open at closed throttle and say 4500rpm +
Then you could retard timing enough to ignite some fuel and air passing through the engine.

It does look cool on some cars though.

[Roverdose]

its not just turbo's, if you watch motogp you will see a few of the bikes popping flames.

Drew

[lumley32]

On the bikes in let them fuel on the under run, it's ment to cool the inlet valves. Plus looks cool!

[86sixsix]

in order of popularity:

bad mapping
anti lag
venting pre-measured air out a valve
roll-on throttle response
engine cooling
impressing people wearing burberry in fast food car parks
having more fuel than money