"Milleron" <millerdot90@SPAMlessosu.edu> wrote in message
news:bvu261hgb7e9u637ihcd3sd211onud70c2@4ax.com...
> On Sat, 16 Apr 2005 18:13:21 GMT, dm@nospam.com (Dave) wrote:
>
> >In article <53d2615793i8pjm3r4disp5enp7d3fgg4m@4ax.com>,
miller.90@spamlessosu.edu wrote:
> >
> >
> >>My guess is that using "plus" or "premium" fuel is not going to give
> >>me a 5% or 10% increase in mileage, but I would have thought that
> >>someone would already have worked this out -- i.e., calculated how
> >>MUCH less the lower octane would have to cost in order to yield an
> >>increase in economy. No? I realize that the EXACT answer depends on
> >>each vehicle's engine-management system, but I'm hoping that there
> >>might be a rule-of-thumb figure. (My car is an '03 Accord EX V6,
> >>BTW.)
> >
> >
> >No data, sorry. But I would be very, very surprised if the fuel
> >economy with the higher grade fuel would be 5% or 10% better. I
> >don't think it has a chance of making up the cost difference. As
> >to performance, I'd even venture that you won't notice a
> >difference. How often do you drive full throttle? Just try it
> >once with each fuel and see if it makes a difference to *you*. My
> >guess: not really. And since Honda says regular unleaded is okay,
> >no worries mate!
>
> Dave,
> I agree thoroughly. I've already tried to notice a difference in
> performance and cannot be sure that there is any -- i.e., if there is,
> it's too subtle for me to be positive.

Same here, my car is rated for regulars gas (but likes ping when using
regular fuel) and I'm hard pressed to notice a performance difference with
the different grades of gas. In my opinion, a more accurate method of figure
out the best type of fuel for the car, is to determine which type of fuel
returns the best mileage. Unfortunately, my car does not have a knock
sensor, so I'm forced to use a higher octane gas. Even though my car demand
the higher octane, performance difference between the two type of fuels
(regular vs premium) is still negligible.

Pars
98 Civic Hatch


Therefore, performance is not
> a significant factor for me, so I was wondering if the more expensive
> fuels might save money in the long run. Like you, my intuition tells
> me that they couldn't be sufficiently more efficient to cover the
> 5-10% increase in cost.
> I'm going to go with that and continue using regular unleaded.
>
>
> Ron

 

On Mon, 18 Apr 2005 19:48:35 -0700, "R. P." <r_pol12gar@hotmail.com>
wrote:

>"John Ings" <nodamned@spam.org> wrote:
>> Lately Honda seems to be engaging in a marketing ploy. Premium fuel is
>> expensive, and people aren't inclined to buy cars that need it, so
>> trusting to the efficiency of its engine knock sensors Honda has
>> recently been recommending regular gas for some of its products that
>> could really use premium! In those cars, the owner's manual says use
>> regular, but premium really will get you another ten HP or so! How do
>> you tell? Well short of a dyno test, check your compression ratio. As
>> a rough rule of thumb (there are a lot of variables) a 9.2 to 1
>> compression ratio Integra 1.8 litre engine only needs 86 octane, while
>> a 10 to 1 VTEC engine needs 91 octane to produce full power.
>>
>> See also http://www.tegger.com/hondafaq/faq.html#premium
>
>Well, that link points out the difference of Octane rating specified by
>Honda and the Octane ratings posted on gas stations:
>
>I read my Honda's Owner's Manual and it says to use 91 "RON".

Where did you buy your Honda? Checking my daughter's 2003 Civic bought
in Canada, the owners manual states:

" Your Honda is designed to operate on unleaded gasoline with a pump
octane number of 86 or higher"

> Almost everywhere in the world, a gasoline is
>referred to by its RON rating. Here in North America however, the MON
>and RON are added together then divided by two to get what we call the
>Anti-Knock Index, or AKI, or "pump octane". So the formula is: (RON +
>MON) / 2 = AKI
>That's why 91 RON is the same as 87 AKI (pump octane).
>91 AKI would be more like 96 or 97 RON. Britain has recently
>re-legalized leaded gas, and "4-star" 97 RON is available once again.
>
>
>Personally, I like to use the medium grade gas for my '94 Accord LX that
>is posted as 89 at the gas pump, using the (R+M)/2 method of
>calculation. I figure that should be well above 91 RON that Honda
>recommends though I still sense some pinging on hot days. I'm not sure
>if it's because the pumps posted Octane numbers are inflated or the
>engine timing is off specs.

I think quoting a RON rating to customers who don't know what it means
is grossly misleading. I wonder where and when Honda did so, and for
how long?

 

Pars wrote:
> It (98 Civic) can get 700km/tank (in the summer) and has been dealer
> maintained since new. The car's tuning is on the ball, it just doesn't have
> the kind of knock sensor found in other engines that are more forgiving.
> It's also a LEV rated vehicle, so the ECU is not antiquated...but I don't
> know if it's OBD-II compatible. Considering that my mileage is in Hybrid
> territory, I'm not complaining.

my 98 hatch is completely OBD2 compatible. i got the scantool for it,
even. the port is under the bolster near your left knee, i think. bout
2" by .75"

 

"John Ings" <nodamned@spam.org> wrote:
> Lately Honda seems to be engaging in a marketing ploy. Premium fuel is
> expensive, and people aren't inclined to buy cars that need it, so
> trusting to the efficiency of its engine knock sensors Honda has
> recently been recommending regular gas for some of its products that
> could really use premium! In those cars, the owner's manual says use
> regular, but premium really will get you another ten HP or so! How do
> you tell? Well short of a dyno test, check your compression ratio. As
> a rough rule of thumb (there are a lot of variables) a 9.2 to 1
> compression ratio Integra 1.8 litre engine only needs 86 octane, while
> a 10 to 1 VTEC engine needs 91 octane to produce full power.
>
> See also http://www.tegger.com/hondafaq/faq.html#premium

Well, that link points out the difference of Octane rating specified by
Honda and the Octane ratings posted on gas stations:

I read my Honda's Owner's Manual and it says to use 91 "RON". What's
that? Isn't that the same as what the pump sticker says? Not
necessarily. That 91 RON is the same as 87 pump octane. The numbers
quotes in the paragraph above are actually pump octanes.

There are two methods used to determine the octane rating of a gasoline:
Motor Octane Number (MON) and Research Octane Number (RON). RON is the
higher of the two. Almost everywhere in the world, a gasoline is
referred to by its RON rating. Here in North America however, the MON
and RON are added together then divided by two to get what we call the
Anti-Knock Index, or AKI, or "pump octane". So the formula is: (RON +
MON) / 2 = AKI
That's why 91 RON is the same as 87 AKI (pump octane).
91 AKI would be more like 96 or 97 RON. Britain has recently
re-legalized leaded gas, and "4-star" 97 RON is available once again.


Personally, I like to use the medium grade gas for my '94 Accord LX that
is posted as 89 at the gas pump, using the (R+M)/2 method of
calculation. I figure that should be well above 91 RON that Honda
recommends though I still sense some pinging on hot days. I'm not sure
if it's because the pumps posted Octane numbers are inflated or the
engine timing is off specs.

R. P.

 

"John Ings" <nodamned@spam.org> wrote in message
news:iba861590v09u36fcjk15fge4vias5fnc6@4ax.com...
> On Mon, 18 Apr 2005 16:49:06 -0400, "Pars" <sdaro(remove)@hotmail.com>
> wrote:
>
> >> It's not fuel injected? Or has your knock sensor come unplugged or
> >> become defective?
> >
> >I wasn't aware that a knock sensor was mandatory for a fuel injected
engine.
>
> If it was sold in Canada or the US it must meet OBD-II specs and would
> have a knock sensor.
>
> >If my 98 Hatch has a knock sensor, if most have an extremely tight
operating
> >range (considering that it will not retard the timing enough to avoid
> >pre-ignition for the recommended fuel...luckily, the high-strung setup
suits my more
> >aggressive driving style).
>
> It may be inoperative, or your ignition timing is grossly misset.

It (98 Civic) can get 700km/tank (in the summer) and has been dealer
maintained since new. The car's tuning is on the ball, it just doesn't have
the kind of knock sensor found in other engines that are more forgiving.
It's also a LEV rated vehicle, so the ECU is not antiquated...but I don't
know if it's OBD-II compatible. Considering that my mileage is in Hybrid
territory, I'm not complaining.

Pars

>
>

 

On Mon, 18 Apr 2005 16:49:06 -0400, "Pars" <sdaro(remove)@hotmail.com>
wrote:

>> It's not fuel injected? Or has your knock sensor come unplugged or
>> become defective?
>
>I wasn't aware that a knock sensor was mandatory for a fuel injected engine.

If it was sold in Canada or the US it must meet OBD-II specs and would
have a knock sensor.

>If my 98 Hatch has a knock sensor, if most have an extremely tight operating
>range (considering that it will not retard the timing enough to avoid
>pre-ignition for the recommended fuel...luckily, the high-strung setup suits my more
>aggressive driving style).

It may be inoperative, or your ignition timing is grossly misset.

 

"John Ings" <nodamned@spam.org> wrote in message
news:sm97619tmios8lpkhrcjr515qkj5396g4e@4ax.com...
> On Sun, 17 Apr 2005 23:03:47 -0400, "Pars" <sdaro(remove)@hotmail.com>
> wrote:
>
> >> >> >If you're light on the gas pedal, the most agreeable fuel will
return
> >the
> >> >> >best mileage
> >> >>
> >> >> Most agreeable? What unit of measure is agreeability calibrated in?
> >> >> Can you find me agreeability ratings for common brands of gas?
> >> >
> >> >The fuel types are premium vs regular as per the orginal post.
> >>
> >> And which is "most agreeable"?
> >
> >For my 98 Civic DX, the most agreeable choice is Premium gas for the
> >summer and Regular for the winter... In the cold weather, there's less
> >chance of mis-fire and perhaps winter blend also plays a factor.
>
> And how did you determine this agreeability?

When mis-firing the engine will exude an un-agreeable amound 'pings'
(or engine knocks). This happen in the summer but not in the winter
(assuming 87 Octane, Regular, fuel is used).

>
> >In the summer, in a effort to save $$$ I'll top-up with Regular if the
tank
> >is already half full of Premium gas (the combination has an adequate
amount
> >of octane to avoid 'pings' for my 98 DX engine).
> >
> >My two favorite gas station is ESSO and Shell. For the Regular gas (87
> >Octane) the ESSO seems to have an higher Octane count then the Shell but
the
> >Shell seems to get slightly better mileage. However, the difference is so
> >minuet, I could be imagining the variation.
> >
> >When comparing fuel consumption between Premium and Regular, My car
return
> >about a 4% variance between the two fuel types. Note, my 98 DX Hatch
doesn't
> >have any sophisticated knock sensor,
>
> It's not fuel injected? Or has your knock sensor come unplugged or
> become defective?

I wasn't aware that a knock sensor was mandatory for a fuel injected engine.
If my 98 Hatch has a knock sensor, if most have an extremely tight operating
range (considering that it will not retard the timing enough to avoid
pre-ignition
for the recommended fuel...luckily, the high-strung setup suits my more
aggressive
driving style).

Pars


>
>
>
>

 

On Sun, 17 Apr 2005 23:03:47 -0400, "Pars" <sdaro(remove)@hotmail.com>
wrote:

>> >> >If you're light on the gas pedal, the most agreeable fuel will return
>the
>> >> >best mileage
>> >>
>> >> Most agreeable? What unit of measure is agreeability calibrated in?
>> >> Can you find me agreeability ratings for common brands of gas?
>> >
>> >The fuel types are premium vs regular as per the orginal post.
>>
>> And which is "most agreeable"?
>
>For my 98 Civic DX, the most agreeable choice is Premium gas for the
>summer and Regular for the winter... In the cold weather, there's less
>chance of mis-fire and perhaps winter blend also plays a factor.

And how did you determine this agreeability?

>In the summer, in a effort to save $$$ I'll top-up with Regular if the tank
>is already half full of Premium gas (the combination has an adequate amount
>of octane to avoid 'pings' for my 98 DX engine).
>
>My two favorite gas station is ESSO and Shell. For the Regular gas (87
>Octane) the ESSO seems to have an higher Octane count then the Shell but the
>Shell seems to get slightly better mileage. However, the difference is so
>minuet, I could be imagining the variation.
>
>When comparing fuel consumption between Premium and Regular, My car return
>about a 4% variance between the two fuel types. Note, my 98 DX Hatch doesn't
>have any sophisticated knock sensor,

It's not fuel injected? Or has your knock sensor come unplugged or
become defective?

 

>
> >> >If you're light on the gas pedal, the most agreeable fuel will return
the
> >> >best mileage
> >>
> >> Most agreeable? What unit of measure is agreeability calibrated in?
> >> Can you find me agreeability ratings for common brands of gas?
> >
> >The fuel types are premium vs regular as per the orginal post.
>
> And which is "most agreeable"?

For my 98 Civic DX, the most agreeable choice is Premium gas for the
summer and Regular for the winter... In the cold weather, there's less
chance of mis-fire and perhaps winter blend also plays a factor.

In the summer, in a effort to save $$$ I'll top-up with Regular if the tank
is already half full of Premium gas (the combination has an adequate amount
of octane to avoid 'pings' for my 98 DX engine).

My two favorite gas station is ESSO and Shell. For the Regular gas (87
Octane) the ESSO seems to have an higher Octane count then the Shell but the
Shell seems to get slightly better mileage. However, the difference is so
minuet, I could be imagining the variation.

When comparing fuel consumption between Premium and Regular, My car return
about a 4% variance between the two fuel types. Note, my 98 DX Hatch doesn't
have any sophisticated knock sensor, so it's totally at the mercy of the
Octane count in the fuel.

I don't know much about the 05 Civic (other then that my 98 Hatch is
noticeably faster...probably do to the fact that my Hatch is LEV while new
Civic is ULEV). Personally, for the 05 Civic, I'd use Regular gas (assuming
it's consumption is equivalent or better then the Premium) and switch to
Premium when entire exhaust system get replace for some performance
enhancement.

Pars
98 DX Hatch

 

On Sun, 17 Apr 2005 14:43:01 -0400, "Pars" <sdaro(remove)@hotmail.com>
wrote:

>> >If you're light on the gas pedal, the most agreeable fuel will return the
>> >best mileage
>>
>> Most agreeable? What unit of measure is agreeability calibrated in?
>> Can you find me agreeability ratings for common brands of gas?
>
>The fuel types are premium vs regular as per the orginal post.

And which is "most agreeable"?

>> >(assuming there is no engine knocking).
>>
>> Knock sensors take care of that.
>
>Not all cars have Knock sensors

A 05 Civic is under discussion.

 

Hi group,

I have a civic 05. My dealer told me that I could just use 87 gasoline
as fuel. I followed his advice and have been using it for four months.
However, this morning when I checked the user manual, I found that I am
supposed to use 91. It amazed me since in my mind 91 is for luxury car,
which my civic apparently is not. Is there any deep reason why Civic has
to use 91? I'd appreciate if you could share me your thought.

Thanks,
Doug

 

"John" <welcomehowcome@hotmail.com> wrote in message
news:xs2dneZdsKZ-Nf3fRVn-3g@comcast.com...
> Sounds like a sales person... buncha words, makes no sense whatsoever. But
> it does use a lot of optimistic sounding words though... gotta love the
> psychology classes these days :/

My Civic DX returns better gas mileage with regular gas vs premium.

btw, here's some psychology. Blow it out your ass. (analyze that)

Pars

>
> "Pars" <sdaro(remove)@hotmail.com> wrote in message
> news:ZMidnVkne8VDq_3fRVn-3Q@rogers.com...
> > If you're light on the gas pedal, the most agreeable fuel will return
the
> > best mileage (assuming there is no engine knocking).
> >
> > Pars
> >
> > "John Ings" <nodamned@spam.org> wrote in message
> > news:1cuv51t5539rv8avv3mgi79h2flugj23jo@4ax.com...
> > > On Fri, 15 Apr 2005 12:10:28 -0400, Douglas Dou
> > > <douglas_dou@yahoo.com> wrote:
> > >
> > > >I have a civic 05. My dealer told me that I could just use 87
gasoline
> > > >as fuel. I followed his advice and have been using it for four
months.
> > > >However, this morning when I checked the user manual, I found that I
am
> > > >supposed to use 91. It amazed me since in my mind 91 is for luxury
car,
> > > >which my civic apparently is not. Is there any deep reason why Civic
> has
> > > >to use 91? I'd appreciate if you could share me your thought.
> > >
> > > Lately Honda seems to be engaging in a marketing ploy. Premium fuel is
> > > expensive, and people aren't inclined to buy cars that need it, so
> > > trusting to the efficiency of its engine knock sensors Honda has
> > > recently been recommending regular gas for some of its products that
> > > could really use premium! In those cars, the owner's manual says use
> > > regular, but premium really will get you another ten HP or so! How do
> > > you tell? Well short of a dyno test, check your compression ratio. As
> > > a rough rule of thumb (there are a lot of variables) a 9.2 to 1
> > > compression ratio Integra 1.8 litre engine only needs 86 octane, while
> > > a 10 to 1 VTEC engine needs 91 octane to produce full power.
> > >
> > > See also http://www.tegger.com/hondafaq/faq.html#premium
> > >
> > >
> >
> >
>
>

 

"John Ings" <nodamned@spam.org> wrote in message
news:aug061l12mq8tqd4vdhvdg6tiut2hqq85j@4ax.com...
> On Fri, 15 Apr 2005 17:49:46 -0400, "Pars" <sdaro(remove)@hotmail.com>
> wrote:
>
> >If you're light on the gas pedal, the most agreeable fuel will return the
> >best mileage
>
> Most agreeable? What unit of measure is agreeability calibrated in?
> Can you find me agreeability ratings for common brands of gas?
>

The fuel types are premium vs regular as per the orginal post.


> >(assuming there is no engine knocking).
>
> Knock sensors take care of that.

Not all cars have Knock sensors


Pars

>
>

 

Nope. Price of 87 Octane here right now is $0.925
a litre.

$0.925 x 3.78L/US Gal = $3.50 CAD/US Gal

$3.50 x $0.78(US Exchange) = $2.73 USD/Gal for
regular friggin gas.

Just over the border from me right now, according
to:

http://www.northdakotagasprices.com/...s&tme_limit=84

the lowest price is $2.09/Gal. It doesn't have
the current price for High Octane, but usually
its either a little cheaper than regular up here
or about the same.

I think i need to move.... lol

t

 

disallow wrote:

> Of course, it helps that premium fuel in the US
> costs less than regular 87 octane does up here,
> but thats my story and i'm stickin to it!

Is that before or after you converted U.S. dollars to Canadian dollars?

 

Just to add fuel to the fire here.... :)

I'm from Canada. I do a fair bit of driving in
the US. It seems as though 87 octane fuel in
Canada works better in my 98 civic than 87
octane fuel in the US. My driving has been
limited to the west coast pretty much.

As a general rule, when I drive in the US, I use
premium fuel. There is a noticeable difference
in the mileage and the performance of the
engine. Mileage is about 5%, and performance
I rate based on how the accelerator feels, and
the vibrations I feel coming from the engine (a
much less imperical measurement).

Of course, it helps that premium fuel in the US
costs less than regular 87 octane does up here,
but thats my story and i'm stickin to it!

t

 

On Sat, 16 Apr 2005 18:13:21 GMT, dm@nospam.com (Dave) wrote:

>In article <53d2615793i8pjm3r4disp5enp7d3fgg4m@4ax.com>, miller.90@spamlessosu.edu wrote:
>
>
>>My guess is that using "plus" or "premium" fuel is not going to give
>>me a 5% or 10% increase in mileage, but I would have thought that
>>someone would already have worked this out -- i.e., calculated how
>>MUCH less the lower octane would have to cost in order to yield an
>>increase in economy. No? I realize that the EXACT answer depends on
>>each vehicle's engine-management system, but I'm hoping that there
>>might be a rule-of-thumb figure. (My car is an '03 Accord EX V6,
>>BTW.)
>
>
>No data, sorry. But I would be very, very surprised if the fuel
>economy with the higher grade fuel would be 5% or 10% better. I
>don't think it has a chance of making up the cost difference. As
>to performance, I'd even venture that you won't notice a
>difference. How often do you drive full throttle? Just try it
>once with each fuel and see if it makes a difference to *you*. My
>guess: not really. And since Honda says regular unleaded is okay,
>no worries mate!

Dave,
I agree thoroughly. I've already tried to notice a difference in
performance and cannot be sure that there is any -- i.e., if there is,
it's too subtle for me to be positive. Therefore, performance is not
a significant factor for me, so I was wondering if the more expensive
fuels might save money in the long run. Like you, my intuition tells
me that they couldn't be sufficiently more efficient to cover the
5-10% increase in cost.
I'm going to go with that and continue using regular unleaded.


Ron

 

On Sat, 16 Apr 2005 16:35:39 GMT, John Ings <nodamned@spam.org>
wrote:

>On Sat, 16 Apr 2005 16:12:36 GMT, Milleron
><millerdot90@SPAMlessosu.edu> wrote:
>
>>>Fill your tank with 87. See how many miles it gets you for how many $
>>>Fill your tank with 91. See how many miles it gets you for how many $
>>>
>>>Ignore miles per gallon. How many miles per dollar did you get?
>>
>>I understand that principle, however, (call me lazy if you want), I'm
>>looking for a simpler answer.
>>I have NO engineering background, so this stuff isn't at all intuitive
>>to me, but it seems as though the only scientific way to do that is to
>>repeat a long trip under exactly the same weather conditions with the
>>ONLY variable being the octane of the fuel used.
>
>If you're interested in precision to three decimal places yes. But are
>you? Of the difference is only a few pennies, what does it matter?
>It's a real saving you're after.
I'm not interested in three decimal places, but I know that it would
be difficult for me to reproduce even the integers (see below), and
that's what I'd need to do to decide if lower-octane gasoline was more
cost efficient.
>
>>My guess is that using "plus" or "premium" fuel is not going to give
>>me a 5% or 10% increase in mileage, but I would have thought that
>>someone would already have worked this out -- i.e., calculated how
>>MUCH less the lower octane would have to cost in order to yield an
>>increase in economy. No?
>
>Maybe somebody has, but as the EPA warns "your milage may vary".
>The best test is your car, with you driving where you most often
>drive. And if the difference between the two fuels is not a
>significant saving for you, go for the 91 octane.

I've kept track of the mileage I get with every single tank of gas
since my 03 Accord was new. The figures vary fairly widely, often by
4 mpg (15%), from tank to tank even though I'm generally "driving
where I most often drive." Therefore, this just wouldn't tell me
anything useful unless the different octanes gave differences
substantially more than 15%, and I know they don't. I just would have
thought that there was a general answer that would apply to most
automobiles with "modern" engine-management systems. I guess there's
not, but thanks very much for the feedback.


Ron

 

In article <53d2615793i8pjm3r4disp5enp7d3fgg4m@4ax.com>, miller.90@spamlessosu.edu wrote:


>My guess is that using "plus" or "premium" fuel is not going to give
>me a 5% or 10% increase in mileage, but I would have thought that
>someone would already have worked this out -- i.e., calculated how
>MUCH less the lower octane would have to cost in order to yield an
>increase in economy. No? I realize that the EXACT answer depends on
>each vehicle's engine-management system, but I'm hoping that there
>might be a rule-of-thumb figure. (My car is an '03 Accord EX V6,
>BTW.)


No data, sorry. But I would be very, very surprised if the fuel
economy with the higher grade fuel would be 5% or 10% better. I
don't think it has a chance of making up the cost difference. As
to performance, I'd even venture that you won't notice a
difference. How often do you drive full throttle? Just try it
once with each fuel and see if it makes a difference to *you*. My
guess: not really. And since Honda says regular unleaded is okay,
no worries mate!

 

On Sat, 16 Apr 2005 16:12:36 GMT, Milleron
<millerdot90@SPAMlessosu.edu> wrote:

>>Fill your tank with 87. See how many miles it gets you for how many $
>>Fill your tank with 91. See how many miles it gets you for how many $
>>
>>Ignore miles per gallon. How many miles per dollar did you get?
>
>I understand that principle, however, (call me lazy if you want), I'm
>looking for a simpler answer.
>I have NO engineering background, so this stuff isn't at all intuitive
>to me, but it seems as though the only scientific way to do that is to
>repeat a long trip under exactly the same weather conditions with the
>ONLY variable being the octane of the fuel used.

If you're interested in precision to three decimal places yes. But are
you? Of the difference is only a few pennies, what does it matter?
It's a real saving you're after.

>My guess is that using "plus" or "premium" fuel is not going to give
>me a 5% or 10% increase in mileage, but I would have thought that
>someone would already have worked this out -- i.e., calculated how
>MUCH less the lower octane would have to cost in order to yield an
>increase in economy. No?

Maybe somebody has, but as the EPA warns "your milage may vary".
The best test is your car, with you driving where you most often
drive. And if the difference between the two fuels is not a
significant saving for you, go for the 91 octane.