[A4] Need for Premium Gas in 1.8T quattro?

[Jim Jordan]

Hi,

Compelled to say that the lower heating value, lhv, of all gasoline is
~17,500 btu/#.  HST, high octane gas has additive(s) to prevent explosions,
pinging, by the faster flame fronts in higher compression engines.  As
mentioned by others there are additives that make higher octane, ergo the
higher price, that also might clean turbos, engine components, etc.  The
only additive that I know of that's worth a hoot is Techron, which Audi at
one point promoted, to be added to fuel in Audi's.  

The newer engines, with knock sensors and electronic timing controls, ought
to be able to advance timing enough to get better mileage with high octane
gas.  However, it might be hard to calculate the savings.  On the other hand
the same knock sensors and electronic timing controls make it possible to
run lower octane without excessive pinging.  

The oil companies are enjoying windfall profits right now;  look for
institutional ads and promotion of higher octane.  Those premium, super
premium, super duper premium ads border on outright misinformation, for they
lead many to use more expensive gas when their vehicles don't require it.

BTW, turbos add volumetric efficiency to ICE's, not compression.  I've been
running the lowest octane, cheapest gas that I could find in my turbo engine
for ~335K miles with no ill effects.  Some of the later model Audi's were
designed for lower compression that made that even more true.

Sorry, but I hate to be grasped thoroughly by the gonads(by the oil
companies) with no way to get loose.

Cheers!

Jim Jordan 

>-----Original Message-----
>From: Grant Lenahan [mailto:glenahan at vfemail.net] 
>Sent: Thursday, September 21, 2006 4:46 PM
>To: thejimrose
>Cc: quattro at audifans.com
>Subject: Re: [A4] Need for Premium Gas in 1.8T quattro?
>
>Nonsense. The main difference between low and high octane is:
>
>1.) more resistance to knock
>2.) sometimes, a better detergent package (since its more expensive)
>
>A turbo engine, by definition, operates at a high effective 
>compression ratio.  So high octane is almost a requirement, 
>mitigated only by an knock sensor which will retard timing and 
>performance to protect the motor.
>
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