[s-cars] S6 pinging woes - the continuation

[joe.pizzimenti at gmail.com]

Preignition, detonation, whatever you want to call it, is bad.

Get the car to another set of ears.  I'm guessing it's rod knock or something in the head that let go.


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-----Original Message-----
From: "Bares, Vittorio" <Vittorio.Bares at nuance.com>

Date: Tue, 28 Jul 2009 07:23:59 
To: Brett Dikeman<brett.dikeman at gmail.com>; Cody Forbes<cody at 5000tq.com>
Cc: <s-car-list at audifans.com>
Subject: Re: [s-cars] S6 pinging woes - the continuation


So what actually causes that nasty 'pa-ping' sound - is that metal on
metal somewhere?

If there is pre-ignition or detonation, both of which I believe result
in the same condition, which is a pre-mature explosion or increase in
pressure in the cylinder which pushes down on the piston while its still
in the up-stroke part of its cycle?

Vittorio -

-----Original Message-----
From: Brett Dikeman [mailto:brett.dikeman at gmail.com] 
Sent: Monday, July 27, 2009 11:44 PM
To: Cody Forbes
Cc: Bares, Vittorio; <s-car-list at audifans.com>
Subject: Re: [s-cars] S6 pinging woes - the continuation

On Mon, Jul 27, 2009 at 10:05 PM, Cody Forbes<cody at 5000tq.com> wrote:

> Even if the problem is pre-detonation pinging by now it is very likely
> that a piston ring or a piston is damaged. In my experiance with these
> engines (I've killed a few of them running over 30psi) it seems the
> pistons are so good that they'll take the detonation for a long time

There are some inaccurate terms being thrown around...

Pre-ignition is when the fuel-air mixture ignites in a controlled burn
but does so prematurely.  Typically a hot spot touches it off, but
there is a relatively smooth progression of the burn.  The burn may
happen more slowly, as compression is lower (flame front speed
increases with compression.)

Detonation is when the fuel doesn't progress in a smooth flame-front
from the plug- ranging from multiple ignition points to spontaneous
combustion of the entire mixture.  I'm not sure if it qualifies for
the chemist's definition of an explosion, but the temperatures and
pressures far exceed normal values.

Brett
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