Don't anybody ever believe that European Gasoline or Japanese Gasoline has a higher octane than ours. I see this all the time "oh, I wish I lived in
insert country here because they have 95 and 98 octane at the pump."
But you aren't figuring the fact of how they calculate octane ratings overseas versus the United States. In the United States, we take the MON, add it to the RON and divide by two. In Europe, they will only use the RON. In essence, Europe and Japan's 98 and 95 octane are equal to our 93 and 91 octane. I kid you not.
In order to better understand gasoline, which some of you desperately need to do to stop from spreading lies, read this website:
Gasoline FAQ - Part 3 of 4
Here's a couple of excerpts:
6.5 What does the Motor Octane rating measure?
The conditions of the Motor method represent severe, sustained high speed,
high load driving. For most hydrocarbon fuels, including those with either
lead or oxygenates, the motor octane number (MON) will be lower than the
research octane number (RON).
Test Engine conditions Motor Octane
Test Method ASTM D2700-92 [104]
Engine Cooperative Fuels Research ( CFR )
Engine RPM 900 RPM
Intake air temperature 38 C
Intake air humidity 3.56 - 7.12 g H2O / kg dry air
Intake mixture temperature 149 C
Coolant temperature 100 C
Oil Temperature 57 C
Ignition Advance - variable Varies with compression ratio
( eg 14 - 26 degrees BTDC )
Carburettor Venturi 14.3 mm
6.6 What does the Research Octane rating measure?
The Research method settings represent typical mild driving, without
consistent heavy loads on the engine.
Test Engine conditions Research Octane
Test Method ASTM D2699-92 [105]
Engine Cooperative Fuels Research ( CFR )
Engine RPM 600 RPM
Intake air temperature Varies with barometric pressure
( eg 88kPa = 19.4C, 101.6kPa = 52.2C )
Intake air humidity 3.56 - 7.12 g H2O / kg dry air
Intake mixture temperature Not specified
Coolant temperature 100 C
Oil Temperature 57 C
Ignition Advance - fixed 13 degrees BTDC
Carburettor Venturi Set according to engine altitude
( eg 0-500m=14.3mm, 500-1000m=15.1mm )
6.7 Why is the difference called "sensitivity"?
RON - MON = Sensitivity. Because the two test methods use different test
conditions, especially the intake mixture temperatures and engine speeds,
then a fuel that is sensitive to changes in operating conditions will have
a larger difference between the two rating methods. Modern fuels typically
have sensitivities around 10. The US 87 (RON+MON)/2 unleaded gasoline is
recommended to have a 82+ MON, thus preventing very high sensitivity fuels
[39]. Recent changes in European gasolines has caused concern, as high
sensitivity unleaded fuels have been found that fail to meet the 85 MON
requirement of the EN228 European gasoline specification [106].
6.9 How is the Octane rating determined?
To rate a fuel, the engine is set to an appropriate compression ratio that
will produce a knock of about 50 on the knockmeter for the sample when the
air-fuel ratio is adjusted on the carburettor bowl to obtain maximum knock.
Normal heptane and iso-octane are known as primary reference fuels. Two
blends of these are made, one that is one octane number above the expected
rating, and another that is one octane number below the expected rating.
These are placed in different bowls, and are also rated with each air-fuel
ratio being adjusted for maximum knock. The higher octane reference fuel
should produce a reading around 30-40, and the lower reference fuel should
produce a reading of 60-70. The sample is again tested, and if it does not
fit between the reference fuels, further reference fuels are prepared, and
the engine readjusted to obtain the required knock. The actual fuel rating
is interpolated from the knockmeter readings [104,105].
6.13 Can higher octane fuels give me more power?
On modern engines with sophisticated engine management systems, the engine
can operate efficiently on fuels of a wider range of octane rating, but there
remains an optimum octane for the engine under specific driving conditions.
Older cars without such systems are more restricted in their choice of fuel,
as the engine can not automatically adjust to accommodate lower octane fuel.
Because knock is so destructive, owners of older cars must use fuel that will
not knock under the most demanding conditions they encounter, and must
continue to use that fuel, even if they only occasionally require the octane.
If you are already using the proper octane fuel, you will not obtain more
power from higher octane fuels. The engine will be already operating at
optimum settings, and a higher octane should have no effect on the management
system. Your driveability and fuel economy will remain the same. The higher
octane fuel costs more, so you are just throwing money away. If you are
already using a fuel with an octane rating slightly below the optimum, then
using a higher octane fuel will cause the engine management system to move to
the optimum settings, possibly resulting in both increased power and improved
fuel economy. You may be able to change octanes between seasons ( reduce
octane in winter ) to obtain the most cost-effective fuel without loss of
driveability.
Once you have identified the fuel that keeps the engine at optimum settings,
there is no advantage in moving to an even higher octane fuel. The
manufacturer's recommendation is conservative, so you may be able to
carefully reduce the fuel octane. The penalty for getting it badly wrong,
and not realising that you have, could be expensive engine damage.
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