Brand of Gasoline

[Cody Forbes]

Generally timing retards will gradually revert after a few seconds. Sometimes it goes by number of successful combustion events with no knock detected, sometimes it's time based. A somewhat typical algorithm is to pull 2 degrees immediately on the first detection, then pull 1 degree on each subsequent detection. Then hold for 0.1-0.5 seconds and start trying to put the timing back 1 degree at a time (0.5s, 1 degree, 0.5s, 1 degree etc). If it then hears another knock it reverts to wherever it stopped the first time. Max retard is typically 10-15 degrees depending on application. 

HOWEVER, many modern systems will have different fuel and ignition (boost too where aplicable) maps for different fuels. If it detects a bunch of knock it can try reverting to a lower octane map. Once that occurs I can't say how long it stays in the other map as I've never researched that one in depth.

-Cody Forbes

On Sep 18, 2012, at 7:01 PM, "Jeremiah Curry" <jeremiah at curryclan.net> wrote:

> I am not expert, but isn't it feasible that with low octane gas in the tank
> you go WOT, maybe to merge on the freeway, leading to detonation.  The
> computer decides to retard timing.  Then the whole time you are on the
> freeway the timing is retarded, leading to less efficient combustion.
> Whereas if higher octane fuel had been used, that would not have happened?
> My understanding is that the decision to retard timing will stay in affect
> for some time.
> 
> I am a convert to premium in vehicles that require it (my Allroad, MR2
> turbo, and Triumph TR3) after having trouble with my 30v Passat and not
> using premium.  However I agree it won't help on engines that don't need it
> (my 80 series Landcruiser)
> 
> Jeremiah
> 
> -----Original Message-----
> From: quattro-bounces at audifans.com [mailto:quattro-bounces at audifans.com] On
> Behalf Of Jeff Waterstreet
> Sent: Tuesday, September 18, 2012 4:17 PM
> To: quattro at audifans.com
> Subject: RE: Brand of Gasoline
> 
> This discussion reminds me why the snake oil sellers and "magical magnetic
> fuel savers" find people to buy their stuff.    Most people don't know how
> to properly monitor their fuel usage, which is evident by many responses to
> this topic.  I especially like those that say "my car just feels peppier"
> when they run premium.    Two of my 8 vehicles require premium (one is a
> 2001 A6Q 2.7T), and there is no difference in mileage between regular and
> premium, unless driven very hard. (like towing a boat, with my other
> "premium" eating vehicle, a Toyota Landcruiser)
> 
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