Read your manual and find out what gas is required would be my advise.

Personally I stay with the 'known' brands and away from the small 'mom
and pop' stores just to insure the gas if fairly fresh.

Don't spend more money than necessary.  If your car says run it on
Regular...run it on Regular.

btw what car do you drive?  We can give a definite answer based on
what you are driving.


Scott in Florida

 Okay, the short answer:  All gasoline sold in your area is the same
raw stuff, shipped through a pipeline to a local tank farm in your
area.  It all meets the same emissions standards, and may have been
refined at a dozen different refineries.

 The only difference is what detergent and additive package they mix
in when they load the fuel into the tank truck for delivery to the
local filling station.  Gasoline headed for a Chevron station gets
Techron additives poured in, Shell gets their V-Power, etc.  The
no-name "Bubba's Gas" independent station gets a generic additive &
detergent package that meets the minimum Federal requirements, period.

 And some of the no-name stores are not as careful to keep water and
dirt out of their tanks, and people have been known to get a load of
bad gasoline full of water - or contaminated with Diesel or Jet Fuel
or god knows what through a goof-up at the tank farm - but that can
happen at both independents and branded stations.

 If your owners manual says 87 octane Regular is okay, use it - if
the car's computer can adjust for the grade of fuel you fill it with,
you are doing nothing but wasting money buying 89 Mid or 91/92
Premium.  There are very few cars sold today that require Premium fuel
exclusively, and they will spell it out in the manual.

 This is a recording...

    --<< Bruce >>--

OK, you guys have made your point. The last thing we want is snobbish
exclusivity. On the other hand, should laziness be ignored?

Having said that, here's my attempt at answering the OP:

Read your owner's manual. Put in what it says.

If your manual advises to avoid fuels with more than 10% ethanol, ask at
the station (or look at the sticker on the pump); don't use that gas.

Generally, all fuels work equally well in most cars. If they do not, you
can switch brands and see if there is a difference. Some cars are finickier
than others. Most cars don't care what you put in it.

Try to fill up at stations with high volume, as the gas will be fresher and
have less water in it.

Keep your tank as full as possible at all times, never letting it get below
half (3/4 is better). This reduces condensation in the tank and reduces
corrosion and deposits in the lines and injectors, as well as extending the
life of your fuel pump.

There are many filters between the station's tanks and  your injectors, so
it is not as necessary as it used to be to avoid filling up at stations
where the tanks are being refilled.

According to the Gasoline FAQ, manufacturers generally put the most (and
best) additives and detergents in their premium fuels as a way of
justifying the higher price. If this is correct, using premium fuels can
help your engine stay cleaner.

When cars get older, combustion chamber deposits can raise the compression
ratio slightly. There is a small possibility that this can cause pinging if
the car is not equipped with a knock sensor. Most--if not all--cars from
about 1993 and up are equipped with knock sensors. If your car has no knock
sensor and you experience pinging under heavy load, you can use a higher
octane in an attempt to relieve the pinging.

Premium fuels generally return about 1% or 2% lower gas mileage than
regular if the car called for regular in the first place. I do not know if
this is also true for cars with knock sensors.

Using premium in a car designed for regular will NOT necessarily result in
more power. Your car needs to be set up to take advantage of the higher
octane. Most cars cannot do this. Instead, the function of the knock sensor  
is effectively to REDUCE power until knocking goes away.

Some gas can cause a rotten-egg smell from brand-new catalytic converters.
This will lessen with time. If you can't wait, try different brands until
the smell goes away.

So in a nutshell, unless you have a Ferrari, it doesn't matter what you put
in your car so long as it meets the specifications in the owner's manual,
and is fresh and clean.

Any more questions?

"Tegger®" <teggeratistopdotcom@changetheobvious.invalid> wrote:

True...(for octane) but the flame front will be slower if the
mixture is leaner. The Argus had spark advance switches which
moved the spark from 20 degrees BTC to 25 BTC. this was
(partially) to recover power which was lost when we leaned the
engines out for cruise. With the mixtures set to 'rich',
advancing the spark from 20 to 25 degrees BTC made a very slight
difference in the torque gauges but when the engines were leaned
to 10% lean then you'd gain about 3 PSI in torque (about 46 BHP).
That's not a large increase for these engines which provided
about 1550 BHP at cruise but helped a little.
--

-Gord.
(use gordon in email)

On Thu, 19 Aug 2004 02:22:53 +0000, Tegger® wrote:

Rats. I hate it when I'm misinformed:

The octane rating of gasoline tells you how much the fuel can be compressed
before it spontaneously ignites. When gas ignites by compression rather than
because of the spark from the spark plug, it causes knocking in the engine.
Knocking can damage an engine, so it is not something you want to have
happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle
the least amount of compression before igniting.

The compression ratio of your engine determines the octane rating of the gas
you must use in the car. One way to increase the horsepower of an engine
of a given displacement is to increase its compression ratio. So a
"high-performance engine" has a higher compression ratio and requires
higher-octane fuel. The advantage of a high compression ratio is that it
gives your engine a higher horsepower rating for a given engine weight --
that is what makes the engine "high performance." The disadvantage is that
the gasoline for your engine costs more.

The name "octane" comes from the following fact: When you take crude oil
and "crack" it in a refinery, you end up getting hydrocarbon chains of
different lengths. These different chain lengths can then be separated
from each other and blended to form different fuels. For example, you may
have heard of methane, propane and butane. All three of them are
hydrocarbons. Methane has just a single carbon atom. Propane has three
carbon atoms chained together. Butane has four carbon atoms chained
together. Pentane has five, hexane has six, heptane has seven and octane
has eight carbons chained together.

It turns out that heptane handles compression very poorly. Compress it
just a little and it ignites spontaneously. Octane handles compression
very well -- you can compress it a lot and nothing happens.
Eighty-seven-octane gasoline is gasoline that contains 87-percent octane
and 13-percent heptane (or some other combination of fuels that has the
same performance of the 87/13 combination of octane/heptane). It
spontaneously ignites at a given compression level, and can only be used
in engines that do not exceed that compression ratio.

  Higher octane gas does burn slower, that's what increases it's  "
RESISTANCE TO EXPLODING ".

 Here is a passage taken from this link on racing fuels:
http://www.klotzlube.com/support/tech_bulletins/gas_dos_and_donts.pdf

Don?t use more octane than you need. "Over Octaning" can actually reduce

performance because of the slower burn speed of high-octane gasoline. Match
the

octane to the compression of your engine.