[vwpassat] Adding "fuel" to the octane argument

[Bob.Sandy at USPTO.GOV]

FWIW, I found this at the Triumphs list
[http://www.mit.edu/people/zimerman/Documents/tr6/octane.html]  regarding a
discussion on Octane. Excerpts are below.  Good reading!

"You should use the lowest octane fuel you can provided the engine shows no
signs of detonation. Octane actually makes the fuel harder to ignite,
hence it's use in very high performance engines. These engines make their
power from the compression, not the octane in the fuel. An engine's power
output is a function of the pressure created in the combustion chamber above
the piston. The more compression, the higher the pressure at the moment
of ignition and the more "push" down on the piston.

As the air/fuel mixture is compressed, the temperature goes up. The more
compression, the higher the temp. At some point, the fuel may spontaneously
ignite prior to the spark plug firing. This is detonation and it is very bad
for an engine because it often occurs just before the plug fires. You then
end up
with two flame fronts in the cylinder that crash into each other which can
crack pistons and rings, etc. Most often in TR engines, I find cracked ring
lands (the area between the topmost two rings) to be the most likely victim
of detonation damage.

Octane is added to the fuel to reduce the chances of detonation. In doing so
it actually slows the combustion process. The lower the octane, the faster
the flame front spreads thoughout the combustion chamber - this yields
higher cylinder pressure just after the piston passes TDC, and theoretically
more power for any given compression ratio provided there is no detonation.
Bottom line - for best performance, run the lowest octane you can that
does not cause detonation."


- Bob


> -----Original Message-----
> From:	vwa1a3b5 at prodigy.net [SMTP:vwa1a3b5 at prodigy.net]
> Sent:	Friday, October 06, 2000 12:56 AM
> To:	vwpassat at egroups.com
> Subject:	[vwpassat] Adding "fuel" to the octane argument
> 
> So does anyone know why octane is added to gasoline?
> Anyone car to guess? 
> 
> I want to clear up with the  1.8T needs 91 octane minimum and how the 
> whole higher octane = more HP thing...
> 
> Does a gallon of 87 have the same BTU (Energy) content as a gallon o 
> f93 octane gas? so why does a gallon of 93 octane have better 
> performance. I know it has something to do with advanced timing and 
> higher compression, but does anyone know exactly why that is?
> 
> Thanks in advance, Carlos
>