[s-cars] Flames, good or bad?

[Paul Gailus]

Another possibility to think about for a rich mixture
is that there could be a significant flow reversion through
the MAF between shifts. Except for those in some recent
high end BMWs and maybe a few other exceptions, MAFs
can not distinguish the direction of the air flow, only the
magnitude.

Ideally the pressure in the intercooler and related plumbing
wouldn't change much between shifts because the
bypass valve opens and maintains enough flow to stay
to the right of the surge line. However, there will be some
drop in the turbo RPM, resulting in a drop in the boost
pressure. As the air flows through the bypass valve, there
will then be a net flow of some of the air mass that was
"stored" under pressure in the intercooler and plumbing
backwards through the MAF. The amount of this air mass
will be proportional to the pressure drop between shifts
and the volume of the intercooler & plumbing.
So if this flow reversion through the MAF is really happening,
then it's possible that a bigger intercooler could cause a larger
reverse flow and a richer fuel mixture between shifts.

Paul

----- Original Message -----
From: Theodore Chen <tedebearp at yahoo.com>
To: <mlped at qwest.net>; Trevor Frank <tfrank at symyx.com>;
<Elijahallen92 at aol.com>; <s-car-list at audifans.com>
Sent: Thursday, January 15, 2004 5:57 PM
Subject: RE: [s-cars] Flames, good or bad?


> spitting flames is something you usually see on carburetor cars,
> during a rapid transition from WOT to closed throttle.  at WOT, fuel
> starts to collect on the insides of the intake, and when the throttle
> is snapped shut, the pressure drops and the fuel goes back into vapor.
> the rich condition results in flames.
>
> i'd guess that in this case, you have a long intake tract that might've
> been made longer by the FMIC.  the MAF is pretty far away from the
> throttle, and when you snap the throttle shut, the engine management
> system is still metering fuel for the greater volume of air that it
> sees moving past the MAF.
>
> i suspect changing the setup so that the turbo blows through the MAF
> would help.
>
> spitting flames probably isn't too good for the catalytic converters.
>
> -teddy
>
> --- mlp qwest <mlped at qwest.net> wrote:
> > So this would be flames on massive deceleration, a suddenly closed
throttle
> > plate?
> > I guess now on re-reading, and paying better attention to Elijah's "..on
> > shifting..."
> > that makes more sense that one could/would generate a lot of unburned
gas
> > pushing through the cylinders coming off the throttle
> >
> > Sorry Elijah.  I guess the next step is to now figure out a way to
measure
> > who's flames the longest?  :-)
> >
> > Mike
> >
> > ~-----Original Message-----
> > ~From: Trevor Frank [mailto:tfrank at symyx.com]
> > ~Sent: Thursday, January 15, 2004 4:10 PM
> > ~To: mlped at qwest.net; Elijahallen92 at aol.com; s-car-list at audifans.com
> > ~Subject: RE: [s-cars] Flames, good or bad?
> > ~
> > ~
> > ~
> > ~At the track many of the urs4 have flames coming out the back, I always
> > ~though it was some issue with too much fuel at or near idle i.e. too
> > ~rich.  But who knows.
> > ~
> > ~I saw brains, haps and I think even chris leals car coming into turn
11,
> > ~a hairpin from a high speed strait shooting flames out the back.
> > ~
> >
> >
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