Better gas mileage with Super octane?

[Rick Courtright]

Things may be different with engines made to run on 87 octane.

Hi,

Your experiment kinda shows what others have experienced, that the $/mi
figure often remains rather constant.

It WOULD be interesting if someone could repeat it with an 87 octane
engine, jumping clear up to the 98. Here in the States we usually only
go as high as your "normal" 92. Don't know if they do any better for
octane across the border on the Canadian side, or if they just stop at
"bigger" gallons!

Rick

 

[Chicobiker]

And then, it could just be a fluke! Here in SoCal, people used to report
they got much better mileage on Arizona gas when they went to Phoenix
and other cities mid-state or so rather frequently. We don't hear that
story so often any more, though.

Believe me, I've also pondered this quite a bit!

I've done the math right. Either way, I was getting more kms driven on
tanks of american gas than on tanks of Canadian gas. I've done 3
vacation road trips into the US, one in the spring around Easter, and
two just after labour day in September, so I don't think it's the
winter-summer mix changeover. I thought that maybe I was driving more
conservatively to avoid the experience of pissing off a state trooper,
but really I think people drive faster on the US side of the border.
On the I95 it seemed like 130kph(80mph) was too slow!!

The best explanation in my mind is that there is something different
about US gas. And if you do the conversion right, US gas is also quite
a bit cheaper!! Gas here is $1.17cdn per litre, which assuming
3.7l/usg and $0.9cdn/USD = $3.90/usgal.

The other thing that crossed my mind is that maybe the highway surfaces
are better/harder? There seems to be more concrete highways in the
states. Or maybe the higher volume of traffic is creating a draft
situation, where following cars have less air resistance!! Yes, I know
- this is not the Tour de France!!

Anyway, somebody asked if we had higher octane premium fuel here? If
we do it's damn rare. Usually it's 87 - 89 - 91 or maybe 93.

Chicobiker

 

[M.J.]

This is no mystery at all, it is a result of added lubricants in the gas!

Premium fuel formulations are just that- premium, for added luxury
and performance. It is not an issue of octane value only. Premium
fuel contains added amounts of detergents to help prevent engine/injector
deposits from forming, and for a more luxurious experience contains
more lubricants that help smooth and quite the engine. Because of added
lubricants there is a very slight, imperceptible almost, improvement in fuel
efficiency.

I drive an 2000 Impreza and almost always buy Chevron Premium fuel.
The car just runs smoother, which I like. This is the softest fuel around
and
smooths the engine beautifully- thanks to lubricants, of course. Chevron
stated
somewhere (I forget where, their official site or somewhere else), that
their Premium grade contains more additives than other Chevron grades.
Other brands probably do the same to their Premium formulations.

M.J.

 

[sarahs choice]

This is no mystery at all, it is a result of added lubricants in the gas!

Premium fuel formulations are just that- premium, for added luxury
and performance. It is not an issue of octane value only. Premium
fuel contains added amounts of detergents to help prevent engine/injector
deposits from forming, and for a more luxurious experience contains
more lubricants that help smooth and quite the engine. Because of added
lubricants there is a very slight, imperceptible almost, improvement in fuel
efficiency.

I drive an 2000 Impreza and almost always buy Chevron Premium fuel.
The car just runs smoother, which I like. This is the softest fuel around
and
smooths the engine beautifully- thanks to lubricants, of course. Chevron
stated
somewhere (I forget where, their official site or somewhere else), that
their Premium grade contains more additives than other Chevron grades.
Other brands probably do the same to their Premium formulations.

M.J.

This may assist.

http://www.shell.com/home/Framework...rists/fuels/optimax/optimax_faqs_ga_1602.html

 

[YKhan]

Things may be different with engines made to run on 87 octane.

I think there might be a different measurement system in North America
than in NZ for octanes. I know that our octane rating system is based
on two previously separate octane ratings, and then an average is taken
between the two.

Yousuf Khan

 

[YKhan]

I did notice however on at least two or three trips into the US that I
got significantly better mileage on american gas. This happened in
both my Subie and my old '95 Accord. I have heard of this before, but
does anybody know what it is about american gas that allows this?

From what I've heard, there is considerable difference in the number of

detergents and other cleaning agents that US gas uses. Namely there's a
lot of it in US premium gas, and not a lot of it in US regular gas. But
in Canada, there should be an equal amount of it in both regular and
premium gas.

Yousuf Khan

 

[YKhan]

First thought is since you're driving in km/hr and getting fuel economy
in mpg, Imp g's at that, your poor computer is just simply confused. And
they think WE'RE crazy south of the 49th with OUR measuring systems!

Nah, I just did the conversion to mpg ahead of time for you guys, since
I know you definitely won't understand our litres/100km gas mileage
rating system. In that system, it's better to have lower numbers for
better gas mileage. You should be able to understand km/h vs. mph, and
imperial vs. US gallons easily though -- at least in relative terms.

But when the last cup of coffee of the day kicks in, it will reveal that
has nothing do do with it, and you may actually have benefited from any
number of things. Was this trip during some of the recent heat wave?

If anything, this trip was during a cooler period. The heat wave had
just ended the week before. It's not cold yet, but it's milder than
during the heat wave period.

Higher temps = thinner air for less wind resistance. They also cause the
tires to run warmer, effectively raising the pressure. Higher pressure
usually = better mpg. Maybe there was a change in wind. Maybe, since I
once experienced a similar thing (long trip, small town gas station, out
of both low and med grades, had to fill up on the 'spensive juice) when
my Loyale, that was very consistent at 27-29 mpg on similar trips, and
only rarely broke 30 with a light foot and careful adherence to a
slightly lower speed than usual, turned in 38 mpg despite no respect for
a particular speed, we were fully loaded, and a coupla other "mileage
killer" factors were in play. I wrote it off as a total fluke, cuz it
never did anything like that again. Later experiments w/ higher grade
fuel showed it to be a false economy for that car. As the others have
said, one trip doesn't tell enough of the story to rely on.

Judging by the various responses here, there seems to be something to
this higher mileage for more expensive gas thing. Maybe the oil
companies can't legally claim you'll get better gas mileage with higher
octane fuels because they may not be able to guarantee it in all
conditions, but there may be some conditions where this holds true.

Yousuf Khan

 

[Clifford Heath]

I think there might be a different measurement system in North America
than in NZ for octanes. I know that our octane rating system is based
on two previously separate octane ratings, and then an average is taken
between the two.

Interesting. In Australia we use RON, determined in a standard
test engine, whereas in the USA, you use an AKI, Anti-Knock-Index.
98RON is about 93 AKI, 92 RON is about 87. Source:
<http://en.wikipedia.org/wiki/Octane_rating>

Thanks for the pointer.

 

[YKhan]

Interesting. In Australia we use RON, determined in a standard
test engine, whereas in the USA, you use an AKI, Anti-Knock-Index.
98RON is about 93 AKI, 92 RON is about 87. Source:
<http://en.wikipedia.org/wiki/Octane_rating>

Thanks for the pointer.

Yeah exactly, our index is a halfway point between the RON number and
the MON number. We don't normally see more than 91 AKI gas around here,
which would correspond to 96 RON for you guys.

Yousuf Khan

 

[Clifford Heath]

We don't normally see more than 91 AKI gas around here,
which would correspond to 96 RON for you guys.

That's available too. Some places even have all three.

 

[Rick Courtright]

Nah, I just did the conversion to mpg ahead of time for you guys, since
I know you definitely won't understand our litres/100km gas mileage

Hi,

You know I was just funnin' ya! The computer doesn't care WHAT system
you use when it's figuring how much fuel to meter out... but I will
admit I always have to think twice to make sure I go from distance/vol
of fuel with MPG to the reverse with L/100KM (which is about the only
metric conversion I can think of right now that makes NO sense to me!
Seems to involve a bit more computation than necessary. Maybe I just
haven't looked at it close enough?)

If anything, this trip was during a cooler period. The heat wave had
just ended the week before. It's not cold yet, but it's milder than
during the heat wave period.

As we've mentioned, there are just TOO MANY variables to predict gas
mileage. For example, conventional wisdom as I've heard it is that the
engine will run better in cooler temps, cuz the denser air contains a
higher amount of oxygen per unit volume, yet my experience has always
been I get better economy in hotter temps. I've always attributed that
to lower wind resistance and a probably increase in tire pressure.
Especially since I notice the differences more when on longer trips when
I can just get out and cruise at steady speeds for a while.

Has anyone else noticed that kind of thing?

Rick

 

[Chicobiker]

admit I always have to think twice to make sure I go from distance/vol
of fuel with MPG to the reverse with L/100KM (which is about the only
metric conversion I can think of right now that makes NO sense to me!
Seems to involve a bit more computation than necessary. Maybe I just
haven't looked at it close enough?)

Can't say I understand the reasons why L/100km was chosen as opposed to
km/L, which would have been a simple multiplication factor. Monkeys
must have come up with the idea.

higher amount of oxygen per unit volume, yet my experience has always
been I get better economy in hotter temps. I've always attributed that
to lower wind resistance and a probably increase in tire pressure.
Especially since I notice the differences more when on longer trips when
I can just get out and cruise at steady speeds for a while.

Has anyone else noticed that kind of thing?

Me. I always thought it was because the temperature of the air going
into the engine was closer to ideal. But then, if it gets too hot I
turn the a/c on!!

Chicobiker

 

[Yousuf Khan]

Just to follow up on this thread. I've just tried my second tankful of
other-than-regular, this time I filled with 89 octane mid-grade; it took
a while to empty the last tank as I haven't been on the highway in a
couple of weeks, which is what I use my car mostly for these days.
There's something definitely going on here that's helping. I managed to
get 9.4 l/100km (30 mpg Canadian) with this tankful. This included some
significant amount of city driving too, not all just highway like
before. The engine feels a lot smoother too. I've occasionally had
hesitations in the past when starting off from a stoplight, a somewhat
occasional jerk or bucking. Haven't noticed it at all since doing the
switch.

Now in my original message (quoted below) I said that I got 31 mpg on
the half tank of 91 octane high-grade I took last time. But I don't
think that means that the higher octane I take, the better the mileage I
get. It probably just reflects the fact that I measured the last time
after doing nearly 100% highway driving. This session I'd say there was
a about 15-20% city driving involved, so therefore I got 30 mpg instead.
On regular, I used to get 28 mpg on average, driving at the same speed
and on the same road.

Yousuf Khan