RE: RE: Fuel Costs

["Derek van Veen" <derek@xxxxxxxxxxxxxx>]

Simply put, the octane rating of a fuel determines the propensity to explode
rather than simply burn when mixed with air and ignited.  Exploding is bad.
Burning is good.  The higher the octane, the more resistant to exploding.

If you are running too low of an octane for your motor, you will get
pinging.  Pinging in its extreme form is also known as detonation.  The
fuel/air mixture is igniting all at once and exploding instead of igniting
as a flame wave.  The resultant "bang" is very hard on the pistons, head,
rods, and cranks.  I've seen bent rods, cracked heads, pounded-out crank
bearings, cracked piston skirts, and chainsawed crankcases (*really* bad
thrown rods!).

In an overly-simplistic nutshell (sorry JC!), chipping a motor will usually
advance the ignition timing, adjust the fuel/air ratio, and modify several
other highly proprietary and secret things to increase performance.  Among
the main factors in detonation are (1) heat; (2) compression ratio; (3)
octane rating; (4) fuel/air ratio; (5) ignition timing.  Modifying any of
these factors can either increase or decrease the propensity to detonate.
Advance the ignition timing and you increase the potential to detonate.
Retard the timing and you decrease the potential to detonate.  You can
balance these factors by modifying some to offset others.  If you increase
the fuel/air ratio and advance the timing, you can raise the octane and end
up with more-or-less the same propensity to detonate as the non-modified
motor.  Alternately, you could lower the compression ratio, but this would
cause a loss of horsepower and efficiency and undo all the gains of
modifying the mix and the timing.

This is a very OVER SIMPLIFIED explanation, so please keep the flames to a
minimum if I over generalized.

- -Derek
 '90 325is

> Date: Wed, 12 Jan 2000 16:23:10 -0500 (EST)
> From: Moe Drippins <ug@domain.elided>
> Subject: RE:  Fuel Costs
>
> ToMoyer@domain.elided writes:
>
> > To the guy that put the chip, etc. in his car, you wanted the extra
> > performance, put in the best gas you can buy, at least 92 octane or
> > watch it slowly self destruct.
>
> What exactly self-destructs with lower octane fuel; the chip?  How
> (and why?)

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