RE: [ST] Octane

["Heyer, Matthew A." <mheyer@xxxxxxxxx>]

OK.  As has been said here, octane is an anti-knock ratio.  It all gets
back to the equation PV=mRT.  On the compression stroke as the pressure
increases, so does the temperature.  Every substance has a temperature
at which it "auto-ignites".  On higher compression ratio engines,
running lower octane fuel will cause the auto-ignition temperature to be
reached and the fuel will ignite before TDC (Top Dead Center) of the
piston stroke.  Once the fuel ignites, it is expanding and pressing
against the piston forcing it down.  When this occurs before the top of
the stroke, you get "knock" and the engine is working against itself and
you are losing power.  In order to run an appropriate fuel so that this
does not happen, a manufacturer will designate the minimum octane of
fuel that must be used in order to prevent this (that is, specifying a
fuel with an auto-ignition temperature sufficiently high so that it does
not auto-ignite during the compression, and thus will only ignite when
the engine designates with the spark).  Running a higher octane is
unnecessary - it simply means that you are running a fuel with an even
higher auto-ignition temperature.

Hope that helps.  

Matt Heyer

(checking back in from a nice little gallivant in Scotland and England -
details to follow)

-----Original Message-----
From: st-triumphnet.com-bounces@xxxxxxxxxxxxxxxxxxxx
[mailto:st-triumphnet.com-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of
brettwilson21@xxxxxxx
Sent: Wednesday, June 15, 2005 11:35 PM
To: ST@xxxxxxxxxxxxxx
Subject: Re: [ST] Octane

Ok Bob you have just got my interest.
 
In our sphere of use I was under the impression that the higher the
octane the bigger the bang so the faster we go, BUT only in an engine
designed and tuned to be run on such fuel. There is no advantage in the
average family car, for instance.
 
E.g. If I run regular unleaded (about 86 - 89 octane in Oz) in my bike
there is a noticable drop in performance. If I run premium unleaded,
anywhere from 92 - 98 octane depending on the vendor, there is a very
noticable pick up in performance.
 
Another interesting fact - A few years back Shell introduced a premium
unleaded fuel and branded it "Optimax". If its run in a carburetted bike
it will foul the plugs within a about one thousand kilometres. Fuel
injected bikes will run on it no problems. No one has been able to find
out why and Shell threw their hands in the air and gave up. I guess as a
group we dont buy enough of it. Their official recommendation is not to
run it in carburreted bikes.
 
Perhaps there is someone on this list that knows more about such things.
 
Brett
Sydney
 
-----Original Message-----
From: Bob Floyd <monobldg@xxxxxxxxxxx>
To: ST@xxxxxxxxxxxxxx
Sent: Wed, 15 Jun 2005 09:06:35 -0700
Subject: [ST] Octane


Alright. I have to vent, and if need be, re-educated.

>From time to time I have seen reference made to "premium", "high
octane",
"the good stuff" etc, in connection with pump gas. In some form or
other,
this is virtually always in the context, or in some form of, getting the
best performance from your ride. 

This makes ZERO sense to me! I'm no rocket scientist, but I do know that
octane is, in fact, a combustion RETARDER. It is used in race and other
high
performance bikes specifically because of that. Higher octane levels
allow
tuners to raise compression, set timing right to the edge, and all sorts
of
other trick stuff while avoiding the resultant potential byproduct of
pre-ignition. 

Therefore, if you're riding a bike with the normal types of tunes, that
is
to say, one that has as much stress on reliability as performance,
pre-ignition is not likely a problem. If you don't experience "pinging"
(pre-ignition) then there is NO PROBLEM running regular gas! In fact,
you
may actually be cutting performance. This is because regular should
actually
be considered the hotter gas, if you will. If you experience lag when
you
barely open the throttle, it could be because you're running premium
when
regular would actually work better.

I think the oil companies get enough of our money without throwing it
away
on octane. I'd rather spend my pennies on cooler clothes so I can at
least
LOOK fast.

Okay, if I'm wrong, educate me.

Bob Floyd
01 RS
65 BMW R50
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