Octane question (FOr the octane Savvy)

Ok folks I am sure this one has been beaten into the ground many times.
However, I am now on a quest. Sort of. A friend of mine had an interesting
view to share on the topic of 87 octane vs 91 octane (low vs high) Below is
his response to my statement (which is below his).
For the record, he has a Nissan Sentra, Spec-v, his wife has a Dodge Noen
(both run 91) I have a Dodge Dakota, and the bike I was referring to in my
post was my old Suzuki SV650s. (I run 87 in both, as per their owner's
manuals)

Does anyone happen to know where I might find, in writing, on a fuel company's
web site that states that the only difference is the octane rating, and NOT
the detergents? (or proof stating otherwise)
I will be researching as best I can during the weekend, but any direction
would be appreciated.

------------------------------------------------
Yes, i've read some very very extensive articles on gasoline octane. Here's
a few notes:

- 91 will always run better than 87.
- 91 from the different gas companies is all DRASTICALLY different
- Running 91 on a car that doesn't need it WILL NOT damage the car. It will
make it run just the same as what the car is tuned for, but it will allow an
extra margin of safety from unpleasant car conditions (i.e. heat soaked
radiator causing overheating, creating knock conditions, 91 will not require
the ECU to compensate nearly as much or as early as if it was on 87)
- 91 octane at most gas stations will contain extra detergents and cleaners
which will prevent your injectors from clogging up as easy, keep the valves
cleaner, and keep all related fuel lines/pump cleaner and free of debris.
- 91 octane at 76 or Shell is considered the absolute cream of the crop for
Southern California. The difference between these two and
Cheveron/Exxon/Mobil/Generic brand is HUGE. Some stock cars are noticing a
5-15% power drop from just using the wrong brand of 91 octane.
- For reference, your air conditioner will sap around 10% of your cars
horsepower when turned on.
- Also for the record, if you do the math with a 10-11 gallon fillup, thats
only an extra $2 each time you fill up (1-2 times a week means an extra
$8-$16 a month) for a cleaner engine and safer driving condition. Thats
worth the extra cost in my book.

----------------- Original Message -----------------
From: Trey
Date: Jun 3, 2005 4:18 PM

Have you actually read up on what makes 91, 91? or what the three grades do?
If the car is not designed for it, the higher grade can actually damage teh
car. My truck for example, it notes not to run 91.
91 can degrade performance in a car designed for 87. Some cars (like your
spec-v) spec that it will run on 87, but to use 89 for best performance. In
that case, the car WILL run on 87, but the knock sensor will retard the
timing (reducing power) to keep it from knocking. and is able to advance the
timing with the 89.
I remember my motorcycle actually felt down on power when I ran 91, it
actually ran better on 87.
as for being "negligibly more expensive than 87" its about a .$20/gallon
difference. Doesnt sound like much, but when your buying 20 gallons at a
time, and get 12 MPG, it adds up VERY fast. Thats an extra $200 a year Im
just blowing out the tailpipe of the truck.

Gasoline FAQ - Part 1 of 4

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

From Sunoco
http://www.sunocoinc.com/market/tran...tion_fuels.htm
Octane

Octane is a measure of the antiknock quality of gasoline. The octane number
posted on service station dispensers and listed in car owner's manuals is an
average of two measurements: Research octane number and Motor octane number.
These octane numbers are determined using a laboratory test engine operated
at different temperatures and speeds to simulate different driving
conditions. The average of these two numbers, (R+M)/2, provides an
indication of on-road performance. Most car owner's manuals recommend a
certain octane but advise owners to increase octane if they detect audible
knock or unsatisfactory performance.

Many new vehicles are equipped with knock sensors to prevent engine damage
resulting from knock or to enhance performance. When engine knock is
detected, the knock sensor system retards ignition timing until knock is
reduced or eliminated. When ignition timing is retarded, power and
efficiency are reduced so drivers can experience poorer acceleration
performance and gas mileage. These vehicles require a higher-octane fuel to
provide optimum performance.

Sunoco has the distinction of offering a range of gasoline octane levels to
satisfy the vehicle population. Sunoco produced leaded gasolines in the
1970s such as Sunoco 190 with 89 to 90 octane and Sunoco 260 with 97.5 to
98.5 octane. Sunoco's current unleaded gasolines include Economy with an 86
octane and Ultra with 94 octane. In order to provide this high-octane fuel,
Sunoco has tested different octane enhancers over the years. These tests
included oxygenated compounds (methanol, tertiary butyl alcohol (TBA),
ethanol, methyl tertiary butyl ether (MTBE), isopropyl alcohol (IPA), ethyl
tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME)), metal-based
additives (lead, methylcyclopentadienyl manganese tricarbonyl (MMT)) and
aromatic amines.

Sunoco has produced leaded racing gasoline since late the 1970s and unleaded
racing gasoline since the mid-1980s. Typical properties for these fuels are
listed in Table 1. One of the unleaded racing gasolines, Sunoco GT100 is
available at select Sunoco retail stations.

Table 1: Sunoco Leaded and Unleaded Race Fuels


--------------------------------------------------------------------------

Property
Standard
Supreme
Maximal
GT100
GT Plus


--------------------------------------------------------------------------

Specific gravity
0.725
0.715
0.700
0.760
0.735

Octane (R+M)/2
110
112
116
100
104

Research octane
115
114
118
105
109

Motor octane
105
110
114
95
99

Reid vapor pressure
8
8
6
8
9

Distillation






Initial boiling point
90
90
100
90
100

10% evaporated
160
155
150
150
135

50% evaporated
220
215
220
210
200

90% evaporated
260
235
230
230
230

Final boiling point
360
260
260
260
255

Lead
Yes
Yes
Yes
No
No

Color
Purple
Blue
Red
Clear
Light Blue

Oxygen



2.7 wt.
4.5 wt.


--------------------------------------------------------------------------




From the Staging Light
Knock, Knock!
Sounds of an unhealthy engine



Disclaimer: While based on facts about drag racing, this page contains the
personal views and opinions of one racer - Michael Beard



Three weeks ago at Beaver Springs Dragway, Beaver Springs, PA, we used a
higher octane fuel than the usual kind. Typically we use 93 Octane from
Coastal in our Duster drag car, but we decided to try the much-heralded
Sunoco Ultra, which is 94 Octane. The car ran exceptionally well that
weekend, and it seemed that our fuel consumption had decreased. It seemed
obvious that the higher octane provided the engine with more power and
better gas mileage. Hence, you had to wonder what octane was really all
about.
First of all, what do the octane ratings mean? If you have ever been bored
enough while filling up your car at the local gas station, you may have
noticed the stickers on the fuel pumps. One of them indicates that the
method used for calculating the octane number is (RON+MON)/2. The RON refers
to the Research Octane Number, and MON to the Motor Octane Number. The two
numbers are derived from different test conditions. The RON method
represents normal mild driving conditions, while MON tests are done under
severe conditions and high engine speeds.
Sensitivity is the difference between the two octane ratings (RON - MON =
Sensitivity), and indicates how the fuel will respond under different
driving conditions. Gasoline in the United States is required to have a high
MON, thus keeping the Sensitivity number low. This is important because it
means the fuel will operate consistently despite changes in driving
conditions. Now, with some of the basics out of the way, we can ask some
more interesting questions about octane.
The formula (RON+MON)/2 is referred to as the anti-knock index. This leads
us to ask exactly what knock is. A good description comes from E.F. Obert,
in "Internal Combustion Engines and Air Pollution" (1973, Harper & Row).
"During the compression stroke of a spark ignited engine, the pressure,
temperature, and density of the mixture are increased and, depending on the
fuel, chemical reactions ... may begin. The spark ignites the mixture, then
the flame travels across the combustion chamber at a more or less orderly
pace with the pressure rising uniformly throughout the chamber. Ahead of the
flame front, the unburned mixture ... is compressed by the rising pressure,
with an accompanying rise in temperature and density. ... If the ignition
delay (chemical) of the end gas is consumed before the flame arrives,
autoignition takes place. With autoignition, the orderly process becomes
uncontrolled and a violent rise in pressure may occur. Energy may be
liberated at such a rate such that the walls of the chamber ... vibrate, and
knock is said to be present."
The octane rating is the measure of the fuel's resistance to autoignition.
When autoignition occurs the gas pressure wave it causes superimposes on the
normal pressure wave of the combustion chamber. These two waves interact to
create a third sawtooth-shaped wave pattern of pressure oscillations. The
pressure oscillations create the knocking sound. Pressure waves caused by
knock can build up quickly and shorten the life span of an engine.
Knock can be reduced by adding chemicals to the fuel. Common examples are
tetra ethyl lead, aromatics, and oxygenates. While these substances increase
the octane rating, their composition does not contribute to the energy of
the fuel when it is burned. The result may be less energy per unit volume of
fuel used, and thus less efficiency. In short, higher octane fuels may
require more fuel to be burnt in order to produce the same amount of energy.
But wait! Didn't I say at the beginning that we experienced a gain in power
and fuel efficiency?
There is one piece of information we have been missing. The compression
ratio of an engine has a lot to do with knock and the apparent effects of
octane. Compression ratio can be thought of as the pressure in the
combustion chamber. High compression ratio engines have more of a tendency
to knock than lower compression ones. Given what we know, since a low
compression engine is not as likely to knock, it does not require a fuel
with as high of an octane rating. A high compression motor, however, needs
more octane to reduce knock. In such a case, switching to a higher octane
fuel would reduce the effects of knock, leading to a more efficient
combustion process. This creates more power and better fuel economy. Using a
higher octane fuel in an engine that does not experience knock will not help
performance. In fact, if the higher octane was achieved through the use of
oxygenates, higher octane than necessary may actually hinder the performance
of an engine!
The goal, then, is to find a fuel with an octane rating that is high enough
to prevent knock, but not much higher. It is possible that the tiny
performance boost we experienced with the drag car is related to the use of
the higher octane fuel. The compression ratio of our motor may be a
borderline case where it is able to use the slightly higher octane. Sunoco
116 would not help our relatively low compression motor any more than the
Sunoco 94, but it is a necessity in most of today's extremely high
compression race engines. In fact, at over $4.50 per gallon, Sunoco 116
would do nothing more than drain your wallet faster! Technology is not
cheap.
WARNING: Use extreme caution when attempting to use a fuel with a lower
octane! If the octane you use is too low, knock will occur, and your engine
can be damaged. Follow your manufacturer's guidelines as to what octane is
suitable for your vehicle.



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"Trey" > wrote
> Yes, i've read some very very extensive articles on gasoline octane.
> Here's a few notes:
>
> - 91 will always run better than 87.

This is in fact, false. A motor designed for regular may perform poorly
with premium.

> - 91 from the different gas companies is all DRASTICALLY different

False.

> - Running 91 on a car that doesn't need it WILL NOT damage the car. It
> will make it run just the same as what the car is tuned for, but it will
> allow an extra margin of safety from unpleasant car conditions (i.e. heat
> soaked radiator causing overheating, creating knock conditions, 91 will
> not require the ECU to compensate nearly as much or as early as if it was
> on 87)

In general, this is not true; if a motor has knock sensors and was designed
to run on regular, it will not run any better or be "safer" with 91.

> - 91 octane at most gas stations will contain extra detergents and
> cleaners which will prevent your injectors from clogging up as easy, keep
> the valves cleaner, and keep all related fuel lines/pump cleaner and free
> of debris.

No. Chevron, for instance, puts the same amount of Techroline in all their
gas.

> - 91 octane at 76 or Shell is considered the absolute cream of the crop
> for Southern California. The difference between these two and
> Cheveron/Exxon/Mobil/Generic brand is HUGE. Some stock cars are noticing a
> 5-15% power drop from just using the wrong brand of 91 octane.

Hard to believe; I doubt it on general principles. If you can find anything
but anectdotal evidence I would be very surprised.

> - For reference, your air conditioner will sap around 10% of your cars
> horsepower when turned on.

If you're talking a 4-cylinder 150hp engine, yes. They take 10-15hp.

> - Also for the record, if you do the math with a 10-11 gallon fillup,
> thats only an extra $2 each time you fill up (1-2 times a week means an
> extra $8-$16 a month) for a cleaner engine and safer driving condition.
> Thats worth the extra cost in my book.

You will gain neither of those (cleaner/safer), so you're wasting your
money.

FloydR - drives BMWs that *do* require and perform better on premium.

"fbloogyudsr" > wrote in message
...
> "Trey" > wrote
>> Yes, i've read some very very extensive articles on gasoline octane.
>> Here's a few notes:
>>
>> - 91 will always run better than 87.
>
> This is in fact, false. A motor designed for regular may perform poorly
> with premium.

I agree it won't run any better. Why would it run worse?

SNIP a bunch of stuff

>> - 91 octane at 76 or Shell is considered the absolute cream of the crop
>> for Southern California. The difference between these two and
>> Cheveron/Exxon/Mobil/Generic brand is HUGE. Some stock cars are noticing
>> a 5-15% power drop from just using the wrong brand of 91 octane.
>
> Hard to believe; I doubt it on general principles. If you can find
> anything
> but anectdotal evidence I would be very surprised.

Shell is making a big deal about its new premium formulation. Whether or
not its any better than anybody elses, who knows?

> FloydR - drives BMWs that *do* require and perform better on premium.

Floyd, I suspect many of the posters on this board drive BMW's.

R / John

"John Carrier" > wrote
> "fbloogyudsr" > wrote
>> FloydR - drives BMWs that *do* require and perform better on premium.
>
> Floyd, I suspect many of the posters on this board drive BMW's.

Yikes; it was late, thought it was a different bbd.

"John Carrier" > wrote in message
...
>
> "fbloogyudsr" > wrote in message
> ...
>> "Trey" > wrote
>>> Yes, i've read some very very extensive articles on gasoline octane.
>>> Here's a few notes:
>>>
>>> - 91 will always run better than 87.
>>
>> This is in fact, false. A motor designed for regular may perform poorly
>> with premium.
>
> I agree it won't run any better. Why would it run worse?
>

Using 91 allows the engine to be build with a higher compression. If you run
a lower compression engine, the air/fuel does not compress enough to take
advantage of its resistance to combustion. The fuel doesn't burn completely,
since it was not ignited in the environment it was designed to ignite in..
so the excess fuel is then burned in the cats... do this for a prolonged
period, and you can burn out the cats.

"Trey" > wrote in message
...
>
> "John Carrier" > wrote in message
> ...
>>
>> "fbloogyudsr" > wrote in message
>> ...
>>> "Trey" > wrote
>>>> Yes, i've read some very very extensive articles on gasoline octane.
>>>> Here's a few notes:
>>>>
>>>> - 91 will always run better than 87.
>>>
>>> This is in fact, false. A motor designed for regular may perform poorly
>>> with premium.
>>
>> I agree it won't run any better. Why would it run worse?
>>
>
> Using 91 allows the engine to be build with a higher compression. If you
> run a lower compression engine, the air/fuel does not compress enough to
> take advantage of its resistance to combustion. The fuel doesn't burn
> completely, since it was not ignited in the environment it was designed to
> ignite in.. so the excess fuel is then burned in the cats... do this for a
> prolonged period, and you can burn out the cats.

Sounds like an urban legend to me. Higher octane isn't combustion
resistance, it's resistance to combustion due to compression. Flame front
propagation after ignition by spark is identical in both fuels ... they both
burn to the same level of completeness.

R / John

John Carrier wrote:
> "Trey" > wrote in message
> ...
>
>>"John Carrier" > wrote in message
...
>>
>>>"fbloogyudsr" > wrote in message
...
>>>
>>>>"Trey" > wrote
>>>>
>>>>>Yes, i've read some very very extensive articles on gasoline octane.
>>>>>Here's a few notes:
>>>>>
>>>>>- 91 will always run better than 87.
>>>>
>>>>This is in fact, false. A motor designed for regular may perform poorly
>>>>with premium.
>>>
>>>I agree it won't run any better. Why would it run worse?
>>>
>>
>>Using 91 allows the engine to be build with a higher compression. If you
>>run a lower compression engine, the air/fuel does not compress enough to
>>take advantage of its resistance to combustion. The fuel doesn't burn
>>completely, since it was not ignited in the environment it was designed to
>>ignite in.. so the excess fuel is then burned in the cats... do this for a
>>prolonged period, and you can burn out the cats.
>
>
> Sounds like an urban legend to me. Higher octane isn't combustion
> resistance, it's resistance to combustion due to compression. Flame front
> propagation after ignition by spark is identical in both fuels ... they both
> burn to the same level of completeness.
>
> R / John
>
>

No, you are dead wrong. Higher octane does translate into (marginally)
slower burning. Not just detonation resistance. Whether it is enough
to allow raw fuel to escape the combustion chamber is dependant on the
engine timing (late ignition and early exhaust valve)

-Fred W