better mileage with higher octane?

is there any truth to the statement that using a higher octane gasoline will result in
better gas mileage? I understand that it may have other beneficial properties ie.
anti-knock, acceleration, etc..

how would one calculate such a statement?

for reference, I usually fillup between 16-20 gallons, regular gas is 87 octane,
supreme 92 octane and in our area the price difference appears to be about 20c-30c
between regular and supreme.

"dido" > wrote in message
...
> is there any truth to the statement that using a higher octane gasoline
will result in
> better gas mileage? I understand that it may have other beneficial
properties ie.
> anti-knock, acceleration, etc..
>
> how would one calculate such a statement?

Dont worry about calculating anything. Octane rating has no direct
relationship
to gas mileage. Antiknock properties are the key.

> wrote in message
. net...
>
> "dido" > wrote in message
> ...
> > is there any truth to the statement that using a higher octane gasoline
> will result in
> > better gas mileage? I understand that it may have other beneficial
> properties ie.
> > anti-knock, acceleration, etc..
> >
> > how would one calculate such a statement?
>
> Dont worry about calculating anything. Octane rating has no direct
> relationship
> to gas mileage. Antiknock properties are the key.
>
and just what do you think Octane rating a measure of?

"stu" > wrote in message
...
>
> > wrote in message
> . net...
> >
> > "dido" > wrote in message
> > ...
> > > is there any truth to the statement that using a higher octane
gasoline
> > will result in
> > > better gas mileage? I understand that it may have other beneficial
> > properties ie.
> > > anti-knock, acceleration, etc..
> > >
> > > how would one calculate such a statement?
> >
> > Dont worry about calculating anything. Octane rating has no direct
> > relationship
> > to gas mileage. Antiknock properties are the key.
> >
> and just what do you think Octane rating a measure of?

The octane rating is, just as I said, a number related to antiknock
properties.

dido wrote:

> is there any truth to the statement that using a higher octane gasoline will result in
> better gas mileage? I understand that it may have other beneficial properties ie.
> anti-knock, acceleration, etc..
>
> how would one calculate such a statement?
>
> for reference, I usually fillup between 16-20 gallons, regular gas is 87 octane,
> supreme 92 octane and in our area the price difference appears to be about 20c-30c
> between regular and supreme.

It varies from car to car depending how clever the ECU is typically.

European and Japanese cars typically prefer higher octane fuels btw. In the UK I've never
seen less than 95RON fuel ( that's 91 in your US PON figures ) and 98 RON is our commonly
available top grade ( 94 PON ).

http://www.btinternet.com/~madmole/R...RONMONPON.html


Graham

wrote:

> "stu" > wrote in message
> > > wrote in message
> > >
> > > Dont worry about calculating anything. Octane rating has no direct
> > > relationship
> > > to gas mileage. Antiknock properties are the key.
> > >
> > and just what do you think Octane rating a measure of?
>
> The octane rating is, just as I said, a number related to antiknock
> properties.

And good anti-knock properties ( higher octane ) allow the ignition to be
advanced which *may* improve engine efficiency. It pretty much invariably
improves performance.

Graham

Eeyore > wrote in article
>...
>
>
> wrote:
>
> > "stu" > wrote in message
> > > > wrote in message
> > > >
> > > > Dont worry about calculating anything. Octane rating has no direct
> > > > relationship
> > > > to gas mileage. Antiknock properties are the key.
> > > >
> > > and just what do you think Octane rating a measure of?
> >
> > The octane rating is, just as I said, a number related to antiknock
> > properties.
>
> And good anti-knock properties ( higher octane ) allow the ignition to be
> advanced which *may* improve engine efficiency. It pretty much invariably
> improves performance.
>
> Graham
>
>
>

In the scenario you describe, the improved performance would come from
physically advancing the timing - NOT from the fuel switch alone.

You could probably see a similar increase by just advancing the timing and
NOT switching fuels - but the engine might suffer.

The simple act of pumping $10 worth of "high test" into the tank of a car
that doesn't require it, really does nothing but improve the bottom line at
corporate headquarters.

On 1/2/07 7:11 AM, in article , "dido"
> wrote:

> is there any truth to the statement that using a higher octane gasoline will
> result in
> better gas mileage? I understand that it may have other beneficial properties
> ie.
> anti-knock, acceleration, etc..
>
> how would one calculate such a statement?
>
> for reference, I usually fillup between 16-20 gallons, regular gas is 87
> octane,
> supreme 92 octane and in our area the price difference appears to be about
> 20c-30c
> between regular and supreme.
>
>

There is qualified truth in your statement. It depends on a number of
factors whether better gas mileage will result from higher octane gas. The
number one factor being that the engine is designed for higher octane gas in
the first place.

Most modern engines have a knock sensor that detunes the engine when it
detects pinging, which is usually due to gas with too low an octane rating.
When it does this the mileage and performance are compromised. Using higher
octane gas in such an engine doesn't necessarily guarantee better gas
mileage but rather it corrects the worse gas mileage that resulted from
running it on the wrong gas.

So, if your owner's manual says you should be using higher octane gas, it
should give better results if you do. If it says you should be using
regular, premium gas will most likely be a waste of money.

"dido" > wrote in message
...
> is there any truth to the statement that using a higher octane gasoline
> will result in better gas mileage? I understand that it may have other
> beneficial properties ie. anti-knock, acceleration, etc..
>
> how would one calculate such a statement?
>
> for reference, I usually fillup between 16-20 gallons, regular gas is 87
> octane, supreme 92 octane and in our area the price difference appears to
> be about 20c-30c between regular and supreme.

Whether or not you get better fuel economy with higher octane gasoline is a
function of the vehicle's PCM (Powertrain Control Module - aka, the engine
computer). If your engine has a knock sensor (or sensors) the PCM may be
able to adjust the engine parameters (mostly spark advance) to increase
performance and fuel economy when you use premium fuel. I've had a couple of
Fords with 5.4L engines. It was claimed that the use of premium fuel would
allow for a 5 to 10 HP increase and a 1% to 3% increase in fuel economy. For
both of these vehicles I ran premium fuel for a significant period of time
(5K+ miles) and compared it to similar periods when I was using regular
fuel. I saw no significant difference in fuel economy. Neither could I tell
there was any difference in performance, although I don't think I could
detect a 10HP increase without a dynometer. The results may vary for other
vehicles. I have noticed that many of the Japanese manufacturers have
started specifying premium fuel for their higher cost engines. I assume that
the major reason for this is achieving slightly better CAFE numbers. I am
confident that most of the vehicles would run OK on regular, perhaps with
slightly worse fuel economy and performance (you should check the owners
guide).

If you are going for maximum MONEY economy (as opposed to maximum fuel
economy), then there is little chance that purchasing premium fuel is a
smart decision. I doubt you will ever increase your fuel economy by more
than 3% by using premium, and since premium costs at least 5% more than
regular, it is a clear loser if you are trying to save money.

A word of caution - you can't really make any determination on the relative
fuel economy difference between regular and premium by comparing single tank
fulls of gas. Besides the inaccuracy of single tank full fuel economy
calculations, you must also consider the actual octane of the fuel mix in
your tank and how quickly the PCM adjusts to different fuels. The PCM will
not instantaneously advance the timing if you start using premium fuel. It
will make the adjustment over a period of time. So if you want to do the
comparison, I'd suggest making the measurement over at least 5 tank fulls of
each type of fuel. I'd also not include two tank fulls when you are
transitioning from one fuel to the other.

Ed

dido wrote:

> is there any truth to the statement that using a higher octane gasoline
> will result in better gas mileage? I understand that it may have other
> beneficial properties ie. anti-knock, acceleration, etc..

I certainly hope so, since my Volvo dealer insists that I need "supreme" and
says exactly that.
>
> how would one calculate such a statement?

By recording the mileage between fillups, and the size of the fillup.
--
derek