Karl is right, the octane rating boosters are just chemicals that lower
the detonation temperature of the fuel air mixture so it doesn't
"explode" all at once before the piston reaches it's power stroke.  The
energy content is the same, but the power produced in an engine will be
reduced if there is detonation rather than an even burn.

Fuel does not explode in the cylinder, it actually burns in a wave, with
the flame front starting at the plug with a spark usually just before
TDC.  The flame continues to burn through the fuel/air mixture as the
piston moves down, creating an even expansion of gasses to produce the
power.  If the fuel detonates all at once (explodes instead of burns
evenly), particularly before TDC, the result is detonation knock, loss
of power, and engine damage.

Modern engines have knock sensors to adjust the engine timing to
eliminate the knock, but the Vanagon does not.  These engines can get
more power with higher octane (to a degree) because the knock sensors
retard the timing for lower octane gas, which reduces the power output.

The only benefit to running higher octane gas in a Vanagon is to
eliminate detonation, or knock.  Use the lowest octane gas that will
prevent knocking when going up hill in a low gear (remove the engine
cover and do a test run, but keep your windows down!).  Using anything
higher will simply line the pockets of the oil companies.

Karl Wolz wrote:
>
> I am not a chemical engineer, but my understanding is that the amount of
> energy in a gallon of gas is the same no matter what the octane.  Higher
> octane gas simply burns more slowly.  This is required in higher compression
> engines where the gas without octane enhancers would start burning all by
> itself before the spark simply from the existing heat and compression.  This
> is preignition, knocking, or pinging.
>
> If someone out there has a more accurate description, or if I'm dead wrong
> here, please let me know (as I know you will!).
>

--
Stuart MacMillan
Manager, Case Program
800-909-8244 ext. 8208

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