better mileage with higher octane?

On Tue, 2 Jan 2007 11:04:16 -0500, "C. E. White"
> wrote:

>"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
>
I have personally had vehicles that cost less to run on premium than
regular - but that was back when the price difference was
significantly less. My daughter's twin cam Neon gets enough better
mileage on mid premium to almost pay the difference (at $0.05 per
liter difference), and it doesn't ping like it does on regular.
Recommendation is premium on that car.


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On Tue, 02 Jan 2007 17:33:30 GMT, CJT > wrote:

wrote:
>
>> "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.
>>
>>
>Precisely. Just think about it -- at one time, octane was increased
>by adding lead compounds. Why would lead increase a fuel's energy?

It didn't - but it allowed the engine to extract more of the energy
that the fuel contained by running at a more efficient setting.

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On Tue, 02 Jan 2007 18:23:01 +0000, Eeyore
> wrote:

>
>
>CJT wrote:
>
>> wrote:
>> > "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.
>> >
>> >
>> Precisely. Just think about it -- at one time, octane was increased
>> by adding lead compounds. Why would lead increase a fuel's energy?
>
>It doesn't. Energy has nothing to do with it.
>
>High octane fuel has less energy than low octane in any case.
>
>Graham

Not necessarily (and usually not) true. This is a MYTH that has been
going around for years. If octane is increased by adding ethanol, it
is true. If it is inproved by catylitic cracking og the feed stock, it
is not true.

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On Tue, 02 Jan 2007 12:40:11 -0600, "*" > wrote:

>
>
>Eeyore > wrote in article
>...
>>
>>
>> * wrote:
>>
>> > Eeyore > wrote
>> > > wrote:
>> > > > "stu" > wrote
>> > > > > > wrote
>> > > > > >
>> > > > > > 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.
>>
>> I don't understand your point.
>>
>> You can't just advance the timing willy nilly. In any case the ECU should
>> control it and any advantage will be gained automatically.
>>
>
>I was thinking pre-computerized ignitions.
>
>So, the ECU has been programmed to advance the timing within safe limits of
>regular fuel....no more.
>
>How do YOU get it to exceed those limits?
>
>
Depends on the ECU. Some can be "chipped" for more advance.Some OBD2
boxes can be "reflashed" Some that still have a distributor can have
the timing physically advanced. On some you can adjust the cam sensor
to provide more advance. On most, it's pretty well "cast in stone"

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"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.
If you turbocharge with enorgh mean pressure to need the extra octane.Your
mileage will improve.
>
>
>



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"*" > wrote in message
news:01c72e9c$e49515a0$5791c3d8@race...
>
>
> Eeyore > wrote in article
> >...
>>
>>
>> * wrote:
>>
>> > Eeyore > wrote
>> > > wrote:
>> > > > "stu" > wrote
>> > > > > > wrote
>> > > > > >
>> > > > > > 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.
>>
>> I don't understand your point.
>>
>> You can't just advance the timing willy nilly. In any case the ECU should
>> control it and any advantage will be gained automatically.
>>
>
> I was thinking pre-computerized ignitions.
>
> So, the ECU has been programmed to advance the timing within safe limits
> of
> regular fuel....no more.
>
> How do YOU get it to exceed those limits?
With a performance chip set.......sold at any rod shop.
And while you are there pick-up your turbocharger kit....and if you want to
use premium
switch to bi-turbo.
>
>
>
>



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Eeyore wrote:
>
> 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
>
>

but only if the computer calls for more timing with higher octane.
If your computer calls for a max of 35 degrees and you can reach that on
regular gas, 91 won't do anything.

That said, I have a Trans Am that will ping if you put in anything lower
than 91. Manual says so, and I accidentially put in a tank of 87 by
accident. Stopped 50 miles later and bought a shot of octane boost and
then filled up again at 1/2 tank to stop the pinging.

Ray

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 may.

As others have stated, octane in itself has nothing to do with fuel
mileage. But increased octance may allow for more spark advance and
more power.

I had a '91 Caprice that I typically ran on 87 octane, but did run on
91/92 octane depending on price. I would typically get 2-3 mpg
better(28 vs 25) on the higher octane fuel. I no longer have the car,
but the price difference between grades has grown to the point that it
probably wouldn't make sense any more anyways.

Try it and find out. But it is unlikely that it will make enough
difference to acount for 30c of price difference.

JW

news wrote:

> Eeyore wrote:
> > 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
>
>
> but only if the computer calls for more timing with higher octane.
> If your computer calls for a max of 35 degrees and you can reach that on
> regular gas, 91 won't do anything.
>
> That said, I have a Trans Am that will ping if you put in anything lower
> than 91. Manual says so, and I accidentially put in a tank of 87 by
> accident. Stopped 50 miles later and bought a shot of octane boost and
> then filled up again at 1/2 tank to stop the pinging.

Saab's Trionic ECUs will deliberately advance the timing until the engine *does*
pink intentionally so. And much much more besides. They even use spark plug
ionisation levels to determine mixture richness ( on a per cylinder basis ) !

They're probably the most advanced around. Many cars have clueless ECUs by
comparison. So it does depend hugely on the car.

Graham

news wrote:

> Eeyore wrote:
> > 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
>
>
> but only if the computer calls for more timing with higher octane.
> If your computer calls for a max of 35 degrees and you can reach that on
> regular gas, 91 won't do anything.
>
> That said, I have a Trans Am that will ping if you put in anything lower
> than 91. Manual says so, and I accidentially put in a tank of 87 by
> accident. Stopped 50 miles later and bought a shot of octane boost and
> then filled up again at 1/2 tank to stop the pinging.

No ECU ? What year is that ?

Graham