More on Top Tier gasoline

"EdV" > wrote
>I hate to bring up the Direct injection thing again, but its related
> to top tier gas.
> True or False?
> Fuels without more detergents/cleaners wont affect a direct injection
> engine as much since the intake valves dont carry gasoline since the
> fuel is injected via nozzles.

As Elmo says, you've got to keep the injectors clean. Diesel engines
have major problems when the fuel is dirty, so I would expect similar
problems, although somewhat reduced due to gasoline's viscosity and
other problems.

However, I have seen a recent post on roadfly on the E90/92 forum
about at least one early 335i having trouble with deposit buildups on
their intake valves. Since gasoline is injected into the cylinder (rather
than intake manifold before the valves), and "bad" things are happening
as far as valve deposits:
http://forums.roadfly.com/forums/bmw...8991298-1.html
As with any anecdote, caution is in order, especially since this isn't
the first direct injection gasoline engine around.

FloydR

Retired VIP wrote:
>
> On Wed, 30 Jul 2008 18:09:05 -0400, "Mike Marlow"
> > wrote:
>
> >
> >"doug" > wrote in message
> ...
> >>
> >>> wow, how uninformed can one person be.
> >>>
> >>>
> >> I wonder - just how uninformed are you? The 3.8 supercharged engine uses
> >> a knock sensor to vary engine operation - higher octane permits it to run
> >> at full optimization. Unless you have a foot of pure lead, this results
> >> in increased engine efficiency/fuel economy.
> >>
> >
> >Yeah - I know. But - real world experience... I owned a 3.8L Supercharged
> >Buick. I saw no significant difference in mileage or performance between 87
> >octane and high octane. The engine adjusts itself to the gas, and optimizes
> >for what's in the tank. Granted - that will be somewhat lower for 87 octane
> >than for high octane, but I never saw enough of a difference to make a
> >difference. Don't know about the other poster Doug - but I'm informed.
> >Beyond what the spec sheet says.
>
> Today's cars don't tune themselves for better performance if you put
> in higher octane gas than they need. They have a default point of
> operation which is usually their most economical operating tune. Only
> if the fuel doesn't meet the engine's requirements does the computer
> de-tune the engine. It the engine is designed to run on 87 octane
> gas, the engine efficiency will be at it's best if you use 87 octane
> gas. You can burn 89 or 91 octane gas in a car designed for 87 with
> no drop in performance or mileage but there won't be any increase over
> what 87 octane provides.

The problem with that is it is a textbook explanation that is outdated
and completely ignores reality. In order to maximize fuel efficiency
and performance many modern engines are programmed to run right up to
the point where detonation occurs. Ideally you would have a small
amount of detonation every firing of a cylinder. Detonation is not
something that is black and white, it is not on or off it is dynamic
and varies in degree. Modern engines are designed to hold the tune so
that detonation is at a point where it maximizes performance. The
knock sensor is not the only thing to respond to more than the minimum
amount of detonation. The air/fuel trim can also respond due to
disruption of complete combustion when detonation exceeds that point
of maximum efficiency.
That means slight changes in octane do make a difference. Couple that
with the fact that octane is a whole lot more complicated than a
single number on a pump. Add to that that the number on the pump is
not as reliable as you might expect and the reality is that no one can
predict the actual mileage effect of going from one brand to the next
or one octane level to the next within one brand. You can read a book
and have it tell you it won't make a difference but you are only
fooling yourself. People who test this in a controlled manner almost
always find some increase in mileage as octane increases. Often that
increase is too small to pay for the extra cost.
It isn't just the fuel that is an unreliable input to your
comfortable formulas it is the engine itself that is unknown quantity.
Lots of things in the engine also affect detonation and thus how much
the engine retunes to accommodate. Even slight changes in engine
temperature affect detonation. So does slight changes in the intake
air temp as well as atmospheric pressure. When a low pressure system
is passing thru everyone's engine is less likely to detonate. And of
course Air/fuel mixture and EGR mix both raise or lower the tendency
to detonate at any particular moment. And then there are slight
defects like vacuum leaks and dirty injectors and dirty or poorly
gapped spark plugs that all affect the engines tendency to knock.
Carbon accumulation in the combustion chamber can also cause
detonation. And what happens then? Well the engine detunes and that
may cause more carbon accumulation. A tank of premium at that point
could break what might become a slow death spiral.

So you tell me you can read a book and read the mfg's specs and tell
me exactly how my engine will react to tank of premium. I don't think
so.


>
> Octane is a measurement of how hard it is to catch the fuel on fire,
> not how much heat energy the fuel contains.

No it is a rating indicating how much the fuel theoretically has a
tendency to detonate. As a counter example to your claim, hydrogen
catches fire much easier than any gasoline component yet it has an
octane rating much higher than any gasoline component.
It is theoretical limit because there is no way to predict with
certainty how any particular blend of fuels will work in any
particular engine. Testing in an engine is still the method for
determining octane even though today they can determine the exact
molecular composition of the fuel.
If someone really want to know how their particular vehicle responds
to any particular gasoline you have to try it and see. It's true the
vast majority of vehicles will see only diminishing returns for octane
levels above what the manufacture recommends. But how much your engine
varies from the norm can only be determined by doing controlled tests.


> The heat energy will be
> about the same in all grades of gas. If ethanol is used as the octane
> booster then 91 octane will have slightly less heat energy since
> ethanol contains about 30% less heat energy than gasoline.

Even when no ethanol is present on average higher octane fuel contains
less energy than low octane. It is just in the nature of the gasoline
fractions that the ones that contribute the most to detonation (for
example heptane) also contain the most energy. But the energy content
is for all practical purposes irrelevant. If energy content was all
that was important for fuel economy then you would burn diesel in your
gas engine.

-jim

>
> The octane requirement of an engine is determined by the engine's
> compression ratio, valve timing, ignition timing, fuel/air mixture,
> etc. The engine computer can control some of these in all engines but
> it can only de-tune to compensate for a fuel that doesn't meet the
> engine's requirements.






>
> A supercharged or turbocharged engine runs at an effectively higher
> compression ratio under boost than it's spec sheet ratio. Boost
> forces more fuel/air mixture into the engine which will raise the
> effective compression ratio. So a boosted engine will almost always
> require premium fuel.
>
> Jack


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> "They fitted cameras to the inside of the combustion chambers"

Combustion chamber viewing was used for the last 100 years to assess
fuel quality. Sir Harry Ricardo was the first to play with it on a
single cylinder variable compression engine with a 1" thick optical
micah viewing port. Pre-ignition and detonation were seen as yellow
colored, and led the the quantification of gasoline's detonation
properties via the octane-heptane ratio.
Many gasoline test engines (variable compression, viewing port with
high speed cameras) are still in use in industry and academia, but are
somewhat obsolete with the introduction of ultra-fast pressure and
temperature sensors and computer modeling.
hth,
Ben

"Retired VIP" > wrote in message
news
> On Wed, 30 Jul 2008 18:09:05 -0400, "Mike Marlow"
> > wrote:
>
>>
>>"doug" > wrote in message
m...
>>>
>>>> wow, how uninformed can one person be.
>>>>
>>>>
>>> I wonder - just how uninformed are you? The 3.8 supercharged engine
>>> uses
>>> a knock sensor to vary engine operation - higher octane permits it to
>>> run
>>> at full optimization. Unless you have a foot of pure lead, this results
>>> in increased engine efficiency/fuel economy.
>>>
>>
>>Yeah - I know. But - real world experience... I owned a 3.8L Supercharged
>>Buick. I saw no significant difference in mileage or performance between
>>87
>>octane and high octane. The engine adjusts itself to the gas, and
>>optimizes
>>for what's in the tank. Granted - that will be somewhat lower for 87
>>octane
>>than for high octane, but I never saw enough of a difference to make a
>>difference. Don't know about the other poster Doug - but I'm informed.
>>Beyond what the spec sheet says.
>
> Today's cars don't tune themselves for better performance if you put
> in higher octane gas than they need. They have a default point of
> operation which is usually their most economical operating tune. Only
> if the fuel doesn't meet the engine's requirements does the computer
> de-tune the engine. It the engine is designed to run on 87 octane
> gas, the engine efficiency will be at it's best if you use 87 octane
> gas. You can burn 89 or 91 octane gas in a car designed for 87 with
> no drop in performance or mileage but there won't be any increase over
> what 87 octane provides.
>
> Octane is a measurement of how hard it is to catch the fuel on fire,
> not how much heat energy the fuel contains. The heat energy will be
> about the same in all grades of gas. If ethanol is used as the octane
> booster then 91 octane will have slightly less heat energy since
> ethanol contains about 30% less heat energy than gasoline.
>
> The octane requirement of an engine is determined by the engine's
> compression ratio, valve timing, ignition timing, fuel/air mixture,
> etc. The engine computer can control some of these in all engines but
> it can only de-tune to compensate for a fuel that doesn't meet the
> engine's requirements.
>
> A supercharged or turbocharged engine runs at an effectively higher
> compression ratio under boost than it's spec sheet ratio. Boost
> forces more fuel/air mixture into the engine which will raise the
> effective compression ratio. So a boosted engine will almost always
> require premium fuel.
>
> Jack

In the past, Ford claimed that the 5.4L V-8, which was intended to run on
regular fuel would have slightly higher fuel economy and slightly more power
if premium fuel was used. Their claim was a maximum improvement of around 3%
increase in fuel economy and maybe an extra 5 horsepower. I don't think must
people could reliably detect either change. I owned 2 Expeditions with the
5.4L V-8 and tried both regular and premium for extended periods and I never
could see any difference in mileage between the two. And there is no way I'd
ever be able to tell the difference between 265 hp and 270 hp just by
driving. I have also compared regular and premium in my Nissan Frontier
(4.0L V-6). Nissan says the truck is designed to run on regular fuel, but
that for maximum economy and performance premium should be used. The first
time I ran premium, the mileage records indicated a significant increase in
fuel economy, However, when I switched back to regular, the mileage stayed
the same. Since then I have tried premium for other extended periods, and
the mileage has not shown any improvement compared to regular.

One factor you guys don't seem to be considering is the effect of the
driver. Knock sensors adjust the engine parameters based on detecting knock.
The PCM doesn't know the type of fuel, only how the engine is reacting as
indicated by the presence of knock. What do you suppose happens in the case
of a driver who is very gentle and never provokes the engine to knock even
when running on regular? I am guessing it will adjust the engine parameters
in the same manner as if the engine was running premium. I suspect this
might be why some people claim significant difference when running premium,
while other (like me) see no difference.

Chevron used to have a really good set of web pages discussing gasoline.
Unfortunately they have replaced those with some advertising inspired
drivel. As I recall, the old Chevron pages addressed the question of energy
content of premium and regular. They claimed premium contained around 3%
more energy than regular on average, but that the energy content of gasoline
in general varied by around this same amount, so in some cases a particular
batch of premium might have less energy than a particular batch of regular.

At least in North Carolina, gasoline samples are routinely checked to verify
the octane.

The gasoline FAQ http://www.faqs.org/faqs/autos/gasoline-faq/part1/ is an
interesting, if not always accurate source of information on gasoline.

Regards,

Ed White

"C. E. White" wrote:
>
> "Retired VIP" > wrote in message
> news
> > On Wed, 30 Jul 2008 18:09:05 -0400, "Mike Marlow"
> > > wrote:
> >
> >>
> >>"doug" > wrote in message
> m...
> >>>
> >>>> wow, how uninformed can one person be.
> >>>>
> >>>>
> >>> I wonder - just how uninformed are you? The 3.8 supercharged engine
> >>> uses
> >>> a knock sensor to vary engine operation - higher octane permits it to
> >>> run
> >>> at full optimization. Unless you have a foot of pure lead, this results
> >>> in increased engine efficiency/fuel economy.
> >>>
> >>
> >>Yeah - I know. But - real world experience... I owned a 3.8L Supercharged
> >>Buick. I saw no significant difference in mileage or performance between
> >>87
> >>octane and high octane. The engine adjusts itself to the gas, and
> >>optimizes
> >>for what's in the tank. Granted - that will be somewhat lower for 87
> >>octane
> >>than for high octane, but I never saw enough of a difference to make a
> >>difference. Don't know about the other poster Doug - but I'm informed.
> >>Beyond what the spec sheet says.
> >
> > Today's cars don't tune themselves for better performance if you put
> > in higher octane gas than they need. They have a default point of
> > operation which is usually their most economical operating tune. Only
> > if the fuel doesn't meet the engine's requirements does the computer
> > de-tune the engine. It the engine is designed to run on 87 octane
> > gas, the engine efficiency will be at it's best if you use 87 octane
> > gas. You can burn 89 or 91 octane gas in a car designed for 87 with
> > no drop in performance or mileage but there won't be any increase over
> > what 87 octane provides.
> >
> > Octane is a measurement of how hard it is to catch the fuel on fire,
> > not how much heat energy the fuel contains. The heat energy will be
> > about the same in all grades of gas. If ethanol is used as the octane
> > booster then 91 octane will have slightly less heat energy since
> > ethanol contains about 30% less heat energy than gasoline.
> >
> > The octane requirement of an engine is determined by the engine's
> > compression ratio, valve timing, ignition timing, fuel/air mixture,
> > etc. The engine computer can control some of these in all engines but
> > it can only de-tune to compensate for a fuel that doesn't meet the
> > engine's requirements.
> >
> > A supercharged or turbocharged engine runs at an effectively higher
> > compression ratio under boost than it's spec sheet ratio. Boost
> > forces more fuel/air mixture into the engine which will raise the
> > effective compression ratio. So a boosted engine will almost always
> > require premium fuel.
> >
> > Jack
>
> In the past, Ford claimed that the 5.4L V-8, which was intended to run on
> regular fuel would have slightly higher fuel economy and slightly more power
> if premium fuel was used. Their claim was a maximum improvement of around 3%
> increase in fuel economy and maybe an extra 5 horsepower. I don't think must
> people could reliably detect either change. I owned 2 Expeditions with the
> 5.4L V-8 and tried both regular and premium for extended periods and I never
> could see any difference in mileage between the two. And there is no way I'd
> ever be able to tell the difference between 265 hp and 270 hp just by
> driving. I have also compared regular and premium in my Nissan Frontier
> (4.0L V-6). Nissan says the truck is designed to run on regular fuel, but
> that for maximum economy and performance premium should be used. The first
> time I ran premium, the mileage records indicated a significant increase in
> fuel economy, However, when I switched back to regular, the mileage stayed
> the same. Since then I have tried premium for other extended periods, and
> the mileage has not shown any improvement compared to regular.
>
> One factor you guys don't seem to be considering is the effect of the
> driver.

That is right. Drivers tend to respond differently to how the car
behaves. Some drivers respond to less power by stepping down on the
gas pedal. Other drivers do just the opposite - when they sense a flat
spot in the acceleration curve as they step on the gas pedal they back
off and stay just below that point. Other drivers are pretty much
oblivious to acceleration and respond to the cars speed.



> Knock sensors adjust the engine parameters based on detecting knock.
> The PCM doesn't know the type of fuel, only how the engine is reacting as
> indicated by the presence of knock. What do you suppose happens in the case
> of a driver who is very gentle and never provokes the engine to knock even
> when running on regular?



Knock is not something that is turned on or off like a light switch.
In a perfect world you would want an engine designed to knock to some
extent at all times (except when decelerating) That would maximize the
amount of energy from each load of fuel and air. That means delivering
the maximum amount of pressure as early as possible from a given
amount of fuel. But there is a limit and going beyond that point does
increase the pressure pulse and that seems like a good thing for fuel
economy but too great a pressure spike (knock is just a pressure
spike)) also destabilizes combustion so going beyond this ideal point
reduces fuel economy. No matter what amount of throttle the driver is
trying to deliver to the wheels you still have this balance point
where any additional leaning of the mixture or advancing of the timing
will result in too much knock (i.e. too big a pressure spike) and not
enough will waste fuel. When the engine is under light load for
maximum fuel efficiency the timing advances and fuel mixtures become
leaner this brings the charge right up to that ideal knock point. But
where that point is can't be predicted - it is arrived at by content
feedback. And there are many things that determine the knock point
besides fuel octane rating. Engine temperature, inlet air pressure and
temperature, EGR volume, compression ratio, spark plug gap and
secondary voltage are some of the things that effect the knock point
in any engine.

In automotive engineering terms what you ask about is called "octane
sensitivity". And one of the problems with the widespread use of
ethanol today is that ethanol is an extremely octane sensitive fuel.
Ethanol used under light loads has an octane capability that is really
no better than mid grade gasoline. But under heavy loads its octane
rating is much much higher than premium fuel. That means adding
ethanol as an octane booster isn't going to help the fuel economy of
the guy "who is very gentle" compared to someone who drives more
aggressively and fast.


There are limits to how much engines can respond to more octane and
when you reach the limit and go beyond usually means less mpg. But
given that most cars today seem to be deigned beyond the limit of base
87 octane fuel and most labeled 87 octane fuel is actually slightly
lower than that labeled 87 octane, it is a fairly safe bet that most
newer cars will get some more miles from higher octane. But if it
isn't more than %5 better then it isn't really going to be worth it.
Most of the time the differences are going to be small and hard to
detect unless you are very meticulous about keeping records and
driving in exactly the same way.

-jim



>I am guessing it will adjust the engine parameters
> in the same manner as if the engine was running premium. I suspect this
> might be why some people claim significant difference when running premium,
> while other (like me) see no difference.
>
> Chevron used to have a really good set of web pages discussing gasoline.
> Unfortunately they have replaced those with some advertising inspired
> drivel. As I recall, the old Chevron pages addressed the question of energy
> content of premium and regular. They claimed premium contained around 3%
> more energy than regular on average, but that the energy content of gasoline
> in general varied by around this same amount, so in some cases a particular
> batch of premium might have less energy than a particular batch of regular.
>
> At least in North Carolina, gasoline samples are routinely checked to verify
> the octane.
>
> The gasoline FAQ http://www.faqs.org/faqs/autos/gasoline-faq/part1/ is an
> interesting, if not always accurate source of information on gasoline.
>
> Regards,
>
> Ed White


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"jim" > wrote in message ...

.....

>> Octane is a measurement of how hard it is to catch the fuel on fire,
>> not how much heat energy the fuel contains.
>
> No it is a rating indicating how much the fuel theoretically has a
> tendency to detonate. As a counter example to your claim, hydrogen
> catches fire much easier than any gasoline component yet it has an
> octane rating much higher than any gasoline component.

Actually hydrogen is not a good example to use. It has a high RON rating
(research method) and a low MON rating (motor method). In an Otto Cycle
engine hydrogen tends to pre-ignite and therefore acts like a low octane
gasoline.

> It is theoretical limit because there is no way to predict with
> certainty how any particular blend of fuels will work in any
> particular engine. Testing in an engine is still the method for
> determining octane even though today they can determine the exact
> molecular composition of the fuel.
> If someone really want to know how their particular vehicle responds
> to any particular gasoline you have to try it and see. It's true the
> vast majority of vehicles will see only diminishing returns for octane
> levels above what the manufacture recommends. But how much your engine
> varies from the norm can only be determined by doing controlled tests.

And as I said before - how you drive will have an effect as well. Someone
who almost never drives at WOT is likely to see less of a difference than
someone who routinely drives hard.

>> The heat energy will be
>> about the same in all grades of gas. If ethanol is used as the octane
>> booster then 91 octane will have slightly less heat energy since
>> ethanol contains about 30% less heat energy than gasoline.
>
> Even when no ethanol is present on average higher octane fuel contains
> less energy than low octane. It is just in the nature of the gasoline
> fractions that the ones that contribute the most to detonation (for
> example heptane) also contain the most energy. But the energy content
> is for all practical purposes irrelevant. If energy content was all
> that was important for fuel economy then you would burn diesel in your
> gas engine.

I was taught that higher octane gasoline had a lower energy content than
regular when I was in college - 30+ years ago. However since then I have
seen many credible sources saying this is not true.

From http://www.api.org/aboutoilgas/gasol...ine-octane.cfm :

"Gasoline with a higher heating value (energy content) provides better fuel
economy. Traditionally, premium gasoline has had a slightly higher heating
value than regular, and, thus, provides slightly better fuel economy, but it
is difficult to detect in normal driving. There can be even larger
differences in heating value between batches of gasoline from the same
refinery, between summer and winter volatility classes, or between brands of
gasoline from different refineries because of compositional differences. The
differences are small and there is no practical way for the consumer to
identify gasoline with a higher-than-average heating value."

Other interesting references:

http://www.sciam.com/article.cfm?id=...tion-premium-g
http://www.consumerenergycenter.org/...s_premium.html
http://ask.cars.com/2007/07/premium-gasolin.html
http://www.cartalk.com/content/featu...ium/myths.html
http://www.caranddriver.com/reviews/...ts+page-2.html
or http://tinyurl.com/6pwz27

It is my opinion that if your car was designed to run on regular, running
premium is a waste of money. Although the engine may be able to adjust some
parameters to increase performance and fuel economy, the changes will be
minor. On the other hand, if your car was designed to run on premium
(because of turbocharging/supercharging, a higher compression ratio, or
other inherent design factors) then running regular may drastically effect
your performance and fuel economy even if the PCM can adjust parameters to
protect the engine from excessive pre-ignition.

Regards,

Ed White

"C. E. White" > wrote
> "Retired VIP" > wrote
>> On Wed, 30 Jul 2008 18:09:05 -0400, "Mike Marlow" wrote:
>>>"doug" > wrote
> In the past, Ford claimed that the 5.4L V-8, which was intended to run on
> regular fuel would have slightly higher fuel economy and slightly more
> power if premium fuel was used. Their claim was a maximum improvement of
> around 3% increase in fuel economy and maybe an extra 5 horsepower. I
> don't think must people could reliably detect either change.

Yeah, I agree. There's a very nice article on Dinan's website about
dynonometer
testing that has a section on 93 vs. 91 octane fuels. They measured an 11
HP
(IIRC - can't get to their website right now) on an E46 M3 - but that's only
3%.
Important on the racetrack, but inconsequential in everyday driving, as 343
hp
is more than sufficient.

> One factor you guys don't seem to be considering is the effect of the
> driver. Knock sensors adjust the engine parameters based on detecting
> knock. The PCM doesn't know the type of fuel, only how the engine is
> reacting as indicated by the presence of knock. What do you suppose
> happens in the case of a driver who is very gentle and never provokes the
> engine to knock even when running on regular? I am guessing it will adjust
> the engine parameters in the same manner as if the engine was running
> premium. I suspect this might be why some people claim significant
> difference when running premium, while other (like me) see no difference.

I completely agree. Although it's likely that, in very well-controlled
experiments premium fuel may give someone with an engine designed
for high-octane fuels a little more mpg, in everyday driving you're not
likely to notice any differences. As I've mentioned in other sub-threads,
the effect on blends, especially of ethanol, is likely to be more
noticeable.

The faq gives some nice info on how closely experiments must be
controlled, particularly temperature. Also, I hadn't really considered the
fact that the high operating temperatures that BMW's are set up for also
increase the need to run them on premium, for max performance.

It's too bad that Jim won't read and believe the faq.

FloydR

"C. E. White" wrote:
>
> "jim" > wrote in message ...
>
> ....
>
> >> Octane is a measurement of how hard it is to catch the fuel on fire,
> >> not how much heat energy the fuel contains.
> >
> > No it is a rating indicating how much the fuel theoretically has a
> > tendency to detonate. As a counter example to your claim, hydrogen
> > catches fire much easier than any gasoline component yet it has an
> > octane rating much higher than any gasoline component.
>
> Actually hydrogen is not a good example to use. It has a high RON rating
> (research method) and a low MON rating (motor method). In an Otto Cycle
> engine hydrogen tends to pre-ignite and therefore acts like a low octane
> gasoline.

Right that is a very definite issue with hydrogen but not an fatal
one. Pre-ignition is not the same thing as detonation altho it may
cause detonation.
Engines have been designed to deal with that. That means high
compression engines that take advantage of hydrogen's octane and are
very efficient compared to gasoline powered engines.


>
> > It is theoretical limit because there is no way to predict with
> > certainty how any particular blend of fuels will work in any
> > particular engine. Testing in an engine is still the method for
> > determining octane even though today they can determine the exact
> > molecular composition of the fuel.
> > If someone really want to know how their particular vehicle responds
> > to any particular gasoline you have to try it and see. It's true the
> > vast majority of vehicles will see only diminishing returns for octane
> > levels above what the manufacture recommends. But how much your engine
> > varies from the norm can only be determined by doing controlled tests.
>
> And as I said before - how you drive will have an effect as well. Someone
> who almost never drives at WOT is likely to see less of a difference than
> someone who routinely drives hard.

Yes depending on what exactly the fuel is composed of. The current
octane rating system is not intended to help motorists with fuel
economy. It is intended to help the oil companies and auto mfgs. sell
there products.


>
> >> The heat energy will be
> >> about the same in all grades of gas. If ethanol is used as the octane
> >> booster then 91 octane will have slightly less heat energy since
> >> ethanol contains about 30% less heat energy than gasoline.
> >
> > Even when no ethanol is present on average higher octane fuel contains
> > less energy than low octane. It is just in the nature of the gasoline
> > fractions that the ones that contribute the most to detonation (for
> > example heptane) also contain the most energy. But the energy content
> > is for all practical purposes irrelevant. If energy content was all
> > that was important for fuel economy then you would burn diesel in your
> > gas engine.
>
> I was taught that higher octane gasoline had a lower energy content than
> regular when I was in college - 30+ years ago. However since then I have
> seen many credible sources saying this is not true.
>
> From http://www.api.org/aboutoilgas/gasol...ine-octane.cfm :

That looks more like a biased opinion not a credible source. The API
is doing a lot of bad mouthing of fuels that contain less heat content
but produce more useful output energy. If you are interested, the API
and SAE do publish figures on heating values for the various classes
of components in gasoline. So you can look at the raw data and judge
for yourself rather than reading the spin they put on that data.


>
> "Gasoline with a higher heating value (energy content) provides better fuel
> economy. Traditionally, premium gasoline has had a slightly higher heating
> value than regular, and, thus, provides slightly better fuel economy, but it
> is difficult to detect in normal driving. There can be even larger
> differences in heating value between batches of gasoline from the same
> refinery, between summer and winter volatility classes, or between brands of
> gasoline from different refineries because of compositional differences. The
> differences are small and there is no practical way for the consumer to
> identify gasoline with a higher-than-average heating value."
>


When they say traditional they mean 50 years ago when the world was
awash in high quality sweet crude oil and large amounts of lead were
used for boosting octane. The reality is octane is achieved in much
different way today and if you look at the class of components that go
into premium compared to what goes into regular from many refineries
the components with higher octane tend to also have less energy. That
doesn't mean it isn't possible to create blends where regular has the
same heat content as premium - it just isn't the current reality.
But the heat content really has nothing to do with fuel economy. Put
some diesel in your gasoline engine and see how much that extra heat
content helps your mileage.

The point I'm making is not that premium is cost effective, but that
you really don't know how any particular engine will respond without
trying it - there are just too many variables for sweeping predictions
to be valid. And this is more true today than in the past because of
the changes engine management systems and changes in fuel. Not because
premium is better but because regular in many places is worse than it
was in the past.

-jim





> > Other interesting references:
> http://www.sciam.com/article.cfm?id=...tion-premium-g
> http://www.consumerenergycenter.org/...s_premium.html
> http://ask.cars.com/2007/07/premium-gasolin.html
> http://www.cartalk.com/content/featu...ium/myths.html
> http://www.caranddriver.com/reviews/...ts+page-2.html
> or http://tinyurl.com/6pwz27
>
> It is my opinion that if your car was designed to run on regular, running
> premium is a waste of money. Although the engine may be able to adjust some
> parameters to increase performance and fuel economy, the changes will be
> minor. On the other hand, if your car was designed to run on premium
> (because of turbocharging/supercharging, a higher compression ratio, or
> other inherent design factors) then running regular may drastically effect
> your performance and fuel economy even if the PCM can adjust parameters to
> protect the engine from excessive pre-ignition.
>
> Regards,
>
> Ed White


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On Mon, 28 Jul 2008 13:02:09 -0700 (PDT), Built_Well
> wrote:

>
>Usually I get 24 miles to the gallon for stop-and-go city
>driving with the '06 Camry LE, but this last tankful I got
>28 city. I really babied the accelerator pedal this time
>and, of course, have plenty of air in the tires. I had
>Shell V-Power premium in the tank this time (for its
>exceptional detergent levels), but usually I just put in
>a regular grade.
>
>I had Hy-Vee Grocery Store premium in there two tankfuls
>back, and thought the car was idling kinda rough sometimes
>while stopped, so I thought some Shell V-Power was in
>order to help clean out any minute amounts of potential
>gunk I might have gotten from the Hy-Vee gas.
>
>When I asked him, the Hy-Vee manager said his gas met
>the Top Tier standard, but Hy-Vee is not on the list
>of Top Tier stations at toptiergas.com, so I doubt
>Hy-Vee is Top Tier.
>
>On Hy-Vee, the car once idled at only 600 rpm; I've never
>seen it idle so low. Usually 650 to 700 is the lowest it'll
>idle at. It could have been a coincidence that the one 600
>idle happened under Hy-Vee.
>
>Quoting the Break Time page at the MFA Oil web site:
>
>"TOP TIER Gasoline is a new class of gasoline with enhanced
>detergency. It meets new, voluntary deposit control standards
>developed by four automotive companies - BMW, General Motors,
>Honda and Toyota - that exceed the detergent requirements
>imposed by the EPA.
>
>"TOP TIER Gasoline keeps engine parts cleaner by reducing
>fuel-related deposits, resulting in better performance.
>A lower level of detergent may cause a buildup of deposits on
>critical engine parts. These deposits can cause stalling,
>rough idling, lowered acceleration and other unnecessary
>problems in your vehicle--and your life.
>
>"TOP TIER Gasoline:
>
>* Improves fuel efficiency
>* Prevents driving upsets (rough idle, hesitation, stalling
> and surge)
>* Improves acceleration
>* Provides more power
>* Reduces emissions
>* Cleans dirty engines and keeps new engines clean
>
>MFA Oil Company is proud to join industry leaders by requiring
>TOP TIER Gasoline with higher levels of detergent in all grades
>and every gallon of gasoline at Break Time Convenience Stores.
>
>Link: http://www.mfaoil.com/index.cfm?show=10&mid=14&pid=4


Two tanks of the non-brand gas and you already have problems ? I think
it's all in your head.
hy-vee is not a gasoline manufacturer. They buy their gas from one of
the big names. There is nothing wrong with the gas, the only
difference could be in detergents. Results will only show up after
many many miles, if ever.
Buying higher grade gas than what the manufacturer of your car
specified is a waste of money.
If you really want to feel better , add a bottle of techron or seafoam
to your tank every 6 months and buy the cheap stuff.
The only gas I don't buy is from small gas stations that don't sell a
lot of gas. They might have old gas and cut corners when changing
filters in their pumps.

On Jul 30, 7:51*am, "Mortimer" > wrote:
> "Retired VIP" > wrote in message
>
> ...
>
>
>
>
>
> > On Tue, 29 Jul 2008 21:17:58 -0700 (PDT),
> > wrote:
>
> >>On Jul 29, 7:13 am, "Elmo P. Shagnasty" >
> >>wrote:
> >>> In article >,
> >>> Fat Moe > wrote:
>
> >>> > As far as getting extra mileage with
> >>> > higher octane? I don't buy it,
>
> >>> Octane is not the issue. Cleanliness of the fuel injectors and intake
> >>> valves and combustion chambers is the issue.
> >>I've had my 98 Pontiac Grand Prix GTP for a little over ten years now,
> >>and follow the gas mileage carefully. Using 92 octane, I will get a
> >>full mile per gallon better than using mid-grade. Using 87 octane will
> >>cost me 3-4 mpg, so it costs me a LOT more by using the cheaper
> >>gasoline. The difference in acceleration is very noticeable as well.
>
> I'm interested that you say you get "a full mile per gallon better". That
> suggests that you normally get results which are consistent to within a
> fraction of an mpg, such that a difference between fuels is significantly
> greater than the difference between successive tank-fillings on the same
> fuel.
>

When I say "a full mile per gallon better ", I mean that driving under
the same type driving conditons, speed, weather, pay load, highway or
city, air conditoner use, etc if I drive the SAME way, I will get one
mile per gallon better on a consistent basis. Have done so for years.
Maybe not a noticeable difference, but the higher octane gasoline is
better for my particular automobile.


> My experience, with both petrol and diesel cars, is that the variation
> between one tank filling and another is about +/- 3 mpg, depending on
> factors such as the type of driving (mainly urban / mainly high-speed / some
> mixture of the two) and different points that different fuel pumps cut off
> when they sense that the tank is full.
>

Of course, if I am driving 85 on the interstate, I will get less
mileage than if I am cruising at 70 (which is the speed I usually use
to test my gas mileage), even less if I slow down to 65 or so.


> My figures are for filling the car to the pump cut-off point and then
> running it until the tank is fairly low - typically for fillings of about 50
> litres (11 gallons UK / 13.5 gallons US) and journeys of around 550-650
> miles.
>

I use my car's on board mileage calculator, which I have tested and
found to be extremely reliable.



> I've noticed a difference in the smoothness of the engine and the
> acceleration between supermarket diesel and BP Ultimate diesel, though some
> of this could be wishful thinking to compensate for the extra cost of BP
> Ultimate - when you pay gold-plated prices maybe your brain thinks it can
> see extra gold-plated performance!- Hide quoted text -
>


I feel the same way about using Shell's Premium. My car runs a little
better on it than on other brands. (At least I THINIK it does!)
> - Show quoted text -