Subject: Re: 2009 A4 TSI

[Huw Powell]

> The difference between regular and premium (high octane) gas is that
> high octane gas has additives which suppress pre-ignition. One of them
> is Tetra-Ethyl-Lead or TEL, a/k/a lead based chemical compounds.

Yes to sentence one.  Not so much to sentence two for the last 40-odd years.

I think the major additive to increase octane is toluene/toluol.

> But I don't think there is any more energy in premium gasoline. It is simply a better quality of the same stuff.

Not "better", just "different".

And then again...

> Not sure if that was true, but they were very good and I never had any trouble again after I started using premium.

Some old wives (read automotive technicians with no training in 
chemistry) aver that the additive package for "premium" contains more 
than just knock-preventing compounds, but also better fuel conditioners, 
for lack of a better phrase.

But I think it's just that running a high compression engine on lower 
octane just mucks it up a bit.  Premium lets it run cleaner.