2009 A4 TSI

Vincent Gelinas vrgelinas at gmail.com
Thu Jun 5 07:26:06 PDT 2014

As far as I know, the energy content (BTU) is the same regardless of the
grade of gasoline used.  The difference comes in the octane rating which
measures the gasoline's resistance to ignition.  The reason premium is
almost required for turbo engines is because the cylinder pressures
generated by the forced induction increase the likelihood of pre-ignition,
where the fuel ignites before the piston is in the power stroke.  This is
also known as knocking and is very bad for the engine.  When knocking is
detected, ignition timing is retarded (pulled) so the spark doesn't occur
until later in the combustion cycle. This leads to more wasted fuel, poorer
fuel economy, and less power because the gasoline doesn't have a chance to
burn completely. When using good quality fuel, the ignition timing can be
advanced a little, where the spark occurs sooner in the combustion cycle.
 The fuel can then be burnt more completely, allowing for more power and
increased fuel economy. Most modern engines are sensitive enough that they
can detect a higher-octane fuel and adjust ignition timing accordingly.

I may have this completely backwards.... feel free to correct me if I do.


On Thu, Jun 5, 2014 at 10:05 AM, Jeremiah Curry <jeremiah at curryclan.net>

> I had a 99 Passat and it started having a lot of trouble running.  Got to
> the point where it would die at ide.  Took it to my Audi specialist and it
> was full of carbon buildup.  He said it was from not running premium.
>  Not sure if that was true, but they were very good and I never had any
> trouble again after I started using premium.  I had always figured since it
> was not a turbo I could just use regular and it would retard timing if
> needed.
> -----Original Message----- From: Nick Lawrence
> Sent: Thursday, June 5, 2014 7:50 AM
> To: quattro at audifans.com
> Subject: Re: 2009 A4 TSI
> I also have trouble with this,   I would like to see a "real time"
> timing display.    Does using regular instead of premium automatically
> retard timing?  Or does the computer  have to sense knock then change
> timing?      I personally haven't seen increased mpg using premium on my
> cars. But I'm generally not on boost a lot.
> Myth busters?
> Nick
> On 6/5/2014 8:37 AM, Paul Caouette wrote:
>> OK!
>> I can't help myself. Please look up the energy per unit volume of
>> "premium" vs "regular" gas.
>> I don't believe it is the fuel.  It is the way it is packed into the
>> space where it is burned that increases the energy available. So, higher
>> compression allows more fuel and oxygen to get pushed into the same volume
>> awaiting that spark that lights it up. When a knock sensor detects a
>> pre-ignituon. (Due to lower grade fuel) it regards the timing of the
>> ignition. This will lead to less energy available in the flame front. But I
>> don't think there is any more energy in premium gasoline. It is simply a
>> better quality of the same stuff.
>> Paul Caouette
>> Sent from my iPhone
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