type of gasoline for civic 05

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

 

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

 

If you're light on the gas pedal, the most agreeable fuel will return the
best mileage (assuming there is no engine knocking).

Pars

 

Most agreeable? What unit of measure is agreeability calibrated in?
Can you find me agreeability ratings for common brands of gas?

Knock sensors take care of that.

 

Thanks for the link. The link essentially says that 87 in pump station
is the same thing as 91 recommended in manual. Can't understand why
Honda does not put 87 in it since the cars are sold in America.

 

No. If the manual says 91 is suitable, then that's the octane that
will give you the most power. If economy is more important to you than
performance, then you can use 87.

The reason is compression ratio. If you have a high enough compression
ratio, then 91 octane is able to give you more power. If you want
economy, the knock sensor will dial back your ignition advance, you
will have less power, but better fuel econmy.

 

Can you spell out what it says exactly,what type of Civic you
have, and where you're posting from? There's always been a problem
with differences in octane rating scales outside the US and Canada
(where RON is typically the pump rating) versus the US and Canada
(where (R+M)/2 - the average of two measurements) is used.

87 octane measured by (R+M)/2 is considered "regular". 91 octane
measured by (R+M)/2 is considered "premium". That 87 (R+M)/2 is
generally equivalent to 91 RON, while that 91 octane (R+M)/2 is pretty
much equivalent to 95 octane RON.

I looked it up, and Honda says the US-spec 2005 Civic Si requires
regular unleaded, but that might be a hedge that it can use it without
destroying itself. The compression ratio of the various Civics
seem to be high - from 9.5 to 9.9. The compression ratio of th
EX and HX versions is slightly higher at 9.9 than that of the Si
at 9.8.

 

In the FAQ, I thought it said "less power and LESS fuel economy."
Which is correct? If the lower octane will definitely give better
fuel economy, then I can live with less power, but that's not how I
thought it worked. Please explain further.

Ron

 

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 :/

 

Less economy in actual miles per gallon. But if the gallon costs
appreciably less...

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. That's pretty
difficult to do in the real world if you're expecting reproducible
accuracy. Isn't there an answer that can be derived from the theory
or measured in dynamometer testing, assuming that 91 (pump) octane
costs 5% more than 89 octane, and 93 octane costs 10% more?

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.)

Thanks

Ron

 

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.

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.

 

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!

 

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.

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

 

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

 

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

 

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

 

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/index.aspx?s=Y&fuel=A&area=Grand%20Forks&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

 

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

Not all cars have Knock sensors


Pars

 

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