unnecessary octane = carbon?

Is there any truth to the oft-repeated wisdom that running high octane (91-93)
gas in a motor that is designed for 87 octane will leave carbon on the pistons,
thus increasing compression and necessitating use of the higher octane until
the carbon is removed? I don't even know where to start in getting to the
bottom of this.

Quite the contrary. A too low octane gasoline will result in carbon buildup when the computer enriches the mixture to prevent pre-ignition and ping. A higher octane gasoline will eliminate the problem.

Ryan Underwood wrote:
>
> Is there any truth to the oft-repeated wisdom that running high octane (91-93)
> gas in a motor that is designed for 87 octane will leave carbon on the pistons,
> thus increasing compression and necessitating use of the higher octane until
> the carbon is removed? I don't even know where to start in getting to the
> bottom of this.

--
Mike Walsh
West Palm Beach, Florida, U.S.A.

No truth to it at all, Ryan.

I remember like it was yesterday how gas station attendants
would warn customers against selecting the highest octane
on the blender pump because it could "burn your valves"


"Ryan Underwood" > wrote in message
...
> Is there any truth to the oft-repeated wisdom that running high octane
(91-93)
> gas in a motor that is designed for 87 octane will leave carbon on the
pistons,
> thus increasing compression and necessitating use of the higher octane
until
> the carbon is removed? I don't even know where to start in getting to
the
> bottom of this.
>

Ryan Underwood wrote:
> Is there any truth to the oft-repeated wisdom that running high octane (91-93)
> gas in a motor that is designed for 87 octane will leave carbon on the pistons,
> thus increasing compression and necessitating use of the higher octane until
> the carbon is removed? I don't even know where to start in getting to the
> bottom of this.

At one time perhaps.

Older higher octane fuel blends tended to be higher in olefins that
might not completely burn and could leave some carbon deposits. All
reformulated gas these days are restricted in the amount of certain
components, including olefins. There are also detergency requirements.
Even if the olefins tend to create carbon, it's not a problem if the
detergent level is high enough to prevent buildup.

<http://www.chevron.com/products/prodserv/fuels/bulletin/phase2rfg/char.shtml>
<http://www.chevron.com/products/prodserv/fuels/bulletin/fed-refm/rfg-char.shtml>

"Ryan Underwood" > wrote in message
...
> Is there any truth to the oft-repeated wisdom that running high octane
(91-93)
> gas in a motor that is designed for 87 octane will leave carbon on the
pistons,
> thus increasing compression and necessitating use of the higher octane
until
> the carbon is removed? I don't even know where to start in getting to the
> bottom of this.
>

Geeze we just saw this one in the chrysler newsgroup again.

The latest theory constructed around this idea is that the knock sensor
doesen't hear the engine knocking so it keeps enrichening the mixture
until it just begins to hear knocking, since it never will due to the high
octane it makes the engine run too rich.

We have one regular poster who believes high octaine gas causes fouling
fervently, most people just give up and ignore these posts.

Ted

its all that sulfer and additives....

.. wrote:
> I remember like it was yesterday how gas station attendants
> would warn customers against selecting the highest octane
> on the blender pump because it could "burn your valves"
>

This is the same kind of misunderstanding that folks talk about with the
high volatility racing fuel- methanol. Or the high energy jet fuel,
etc. If something has high performance it must be because the fuel must
be providing more energy, right? Size of engine, its makeup, power to
weight ratio, all that is too hard to think about- performance must mean
high energy, high volatility, high danger, fuel.

"Don Stauffer" > wrote in message
...
> . wrote:
> > I remember like it was yesterday how gas station attendants
> > would warn customers against selecting the highest octane
> > on the blender pump because it could "burn your valves"
> >
>
> This is the same kind of misunderstanding that folks talk about with
the
> high volatility racing fuel- methanol. Or the high energy jet fuel,
> etc. If something has high performance it must be because the fuel
must
> be providing more energy, right? Size of engine, its makeup, power to
> weight ratio, all that is too hard to think about- performance must
mean
> high energy, high volatility, high danger, fuel.

It was as hilarious then as now.

"Ted Mittelstaedt" > writes:

>The latest theory constructed around this idea is that the knock sensor
>doesen't hear the engine knocking so it keeps enrichening the mixture
>until it just begins to hear knocking, since it never will due to the high
>octane it makes the engine run too rich.

If you were going to use the knock sensor instead of the O2 sensors to
calibrate the mixture, wouldn't you want to LEAN the mixture until it started
knocking, and then slightly richen it from that point? How would you ever get
knocking by continuing to enrich a mixture which is already not knocking?