- 95 octane is normally used, anything above this
can yield more power.
- A great way to get more power for short term use.
- Must be accompanied by a remap, otherwise, less
power may result.
in this country are a bit limited. In most areas there are no options outside of
95octane pump fuel. Some stations provide 97octane.
rallying and other formulas such as drag racing or for trackdays using road
cars, there are a wealth of options available from octane's from 98 upto
120octane and above. Most
competitors and enthusiasts have probably heard of using high octane petrol,
methanol and nitromethane (nitro), but this is only a
small sample of the wide variety of fuels available for occasional use.
Octane Rating. - A measure of a fuels anti-knock capabilities.
- Is not a measure of power potential.
sometimes think that a fuels octane rating is a measure of its power output.
This is not true. In fact changing from 95 octane to 98 octane in a normal road
car, without remapping the ignition map, will probably result in a power loss !!
without a remap or without a knock management system, there is no way for an
engine to take advantage of increased octane ratings.
rating is in fact a measure of a fuels anti-knock capabilities. The higher the
octane rating, the more resistant the fuel is to knocking. The likelihood of
damaging detonation and pre-ignition occurring is lessened by using higher
octane fuel. When the engine is remapped to take advantage of this anti-knock
characteristic then more power is produced.
of Octane Standards.
At the start
of WW1, there was no such thing as an octane rating for fuel. However, it was
found that highly tuned engines in cars and planes reacted differently to
different batches of fuel that was thought to be identical.
Two tins of fuel,
both from the same refinery and both with identical weights etc.. would react
differently in the engine. The engine would run well on one tank of fuel and
when it was refilled it would blow up while running on the other batch of fuel.
weren’t able to distinguish between a good and bad batch of fuel. To overcome
this problem, special single piston fuel research engines were made and
distributed to different labs around the world. The labs
would test the quality of the fuel by running the engine on the fuel and raising
the compression ratio until knocking occurred. This
was called the HUCR rating (Highest Usable Compression
the engines before testing, two pure fuel substitute substances were used to
establish a high and low reference point. The high reference fuel used was
isooctane (2-2-4 trimethylpentane) and the low
reference fuel was heptane (n-heptane).
following method was then used to determine a fuels quality. Firstly, its
HUCR was determined as mentioned previously. Then various
runs would be carried out using different mixes of the high and low reference
fuels, iso-octane and n-heptane until a blend was found that had a knock
behavior identical to the knock behavior of the fuel under test. Then the fuel
under test would be rated according to the percentage of iso-octane and n-heptane
used. So a fuel
that behaved the same as 95%_iso-cotane and 5%_n-heptane would be rated at 95
octane petrol. This is how octane ratings came into widespread use.
and Motor Tests. - Research test, or RON measures the fuels low RPM
- Motor test, or MON measures the fuel high RPM
- MON is more relevant for forced induced engines.
research and motor tests have come into widespread use. The same basic methods
and test engines are still used, but a new test call the motor octane test has
more relevance than the older (but more widespresd)
research octane test. The motor
method uses the same engine, but runs it at a higher rpm and intake temperature
and gets the octane figure based on these conditions – therefore, this test is
more relevant to forced induction engines.
the MON (Motor Octane Number) is more relevant for
highly stressed engines than the RON (Research Octane
Number) but it is the RON number often gets quoted at. This is because, for the
same fuel, the RON number will always be higher than the MON number, and it
sounds better to quote the RON number. Use the MON
number to indicate the knock resistance at high load and RPM. Use the RON
number to indicate the knock resistance at part load and lower RPM.
difference between the RON and MON is called the fuels sensitivity. A typical
batch of fuel could have a RON of 95 and a MON of 85. This means that the fuel
has an octane rating of 95 at low load and an octane rating of 85 at high load. The next
batch of fuel could have the same RON of 95 with a MON of 88. Obviously this
fuel will be better at high engine load even though the RON is the same.
Octane Test. - High octane test, or SON tests for octane's over
which have an octane rating that is higher than 100 have a different test called
the Supercharge test (obviously the traditional tests
won’t work on fuels greater than 100 octane). The
Supercharge Octane Numbers (SON) are got by extending
the old system in a linear fashion beyond 100. In this test the high reference
fuel used is iso-octane with lead additives. Two tests
are carried out, the F3 and F4 tests. The F3 test
is done at cruise and the F4 test is done using full load. This is why
high octane fuels have two numbers eg. 100/130.
Race Fuel. - Used for aviation and competition.
Most of the
older racing fuels are actually Avgas fuels rebadged as racing fuel. ‘Racing
115’ fuel is in fact ‘Avgas 115/145’. Leaded ‘Racing 100’ is the same as ‘Avgas
100/130’. The old green Avgas was used as leaded 108 racing fuel and the newer
blue Avgas was used as unleaded 108 racing fuel. Recently,
Avgas 112/160 has been launched as ‘Racing 108’ leaded fuel.
Motorsport Fuels. - Aviation fuel taylored for motorsport use or
originally derived for motorsport.
A lot of the
big companies produce fuels specifically for motorsport use. These fuels are
designed to give the anti-knock capabilities of Avgas with improved throttle
response and power. Typically, 4-5% at the top end and more at the midrange. In the USA
VP Motorsport 103 is very popular(99MON, 107RON, 3%oxygen). One of the top fuels
in USA is Power-Mist RFG(104MON, 112RON, 6%oxygen). Formula 1
fuel is also top class, but it is somewhat limited by the regulations. F1 fuel
has a maximum RON or 102 and max oxygen content of 2.7% and is made up of toluol,
xylene, sopentane, iso-octane, hexene-1, n-butane, 2-methylpentane.
Boosters. - Selected brands are effective, but some brands
have little effect.
mentioned, toluol and xylene are the main anti-knock agents in F1. In the past,
a good way to increase the anti-knock properties of petrol was to add toluol to
the petrol (upto 33%). However, it can’t be used on
unleaded fuel as a reliable octane booster. The most
effective octane booster is MMT(methyl cyclopentandienyl manganese tricarbonyl).
It is used in NF Racing Formula and Nulon Pro Strength. They will both add 3ron
to 95ron fuel and 1.5ron to 98ron fuel. Most other
octane boosters are less effective. You have to check the contents carefully to
see if it contains any usable chemicals. Also, most of the claims made on the
package are usually not true.
Methanol. - Very high latent heat of vaporisation allows big
power gains up to 20%.
- Requires revised fuel delivery.
octane rating is not the whole story. There are many factors that contribute to
a fuels power potential. Methanol has
a MON of 90 yet can produce power increases of 20% over petrol. Shell ‘A’
racing fuel is 96% methanol and 3% acetone. The key to
methanol is its very high latent heat of vaporisation. It takes a lot of heat to
be converted from liquid to vapour.
Petrol has 135Btu/lb whereas methanol has
472Btu/lb. The heat required for proper atomisation is drawn from the piston
crown, inlet tract, combustion chamber and inlet and exhaust valves. This
results in an internally cooler engine which puts less heat into the inlet
charge, so the charge density goes up and the horsepower goes up. Another
factor acting in methanols favour is the amount of energy available in the
burned fuel. Using petrol, the best power ratio is around 13:1. With methanol
the air/fuel ratio for max power is about 5:1. Because were consuming much more
methanol, were also absorbing more heat from the engine. (Note: this
means we need to flow double the amount of methanol – bigger fuel lines, bigger
fuel pumps, bigger injectors etc…).
downside to using methanol is that it is extremely poisonous. It can slowly
build up inside of you and cause blindness and insanity. It can be absorbed
through the skin and lungs. It is also present in the burnt exhaust gas
especially in rich burning mix.
It can also
be damaging to your engine. It will eat through fiberglass resin. It has a
scouring effect on tanks and fuel lines. It will absorb high
amounts of water so it must be kept airtight. After use the whole system has to
be flushed out with petrol. It promotes water induced rust and corrosion inside
the engine. It is particularly damaging to aluminum and zinc. It regularly leads
to blocked injectors. Methanol does not lubricate like petrol, so flat-slide
and barrel-type throttles tend to stick on methanol. In colder climates starting
problems will be experienced. Methanol burns much more
slowly than petrol so the ignition needs to be advanced.
Nitro methane. - Can double the power output.
- Used on drag cars.
doesn’t even have an octane rating because it is too variable, yet it can more
than double a petrol engines power. This is because extremely rich mixtures can
be used and because of its unique chemical makeup. Nitro methane contains 53%
oxygen so it permits large quantities of fuel for conversion to heat energy.
Because it burns so slowly, it keeps pushing the piston to the bottom of the
to be mixed with methanol for use in drag racing, but nowadays nitro is used
with almost no methanol blended in. It is
necessary to reduce the compression ratio in engines to protect against
detonation. The air/fuel mix must always be set very rich, sometimes 2:1. Igniting
nitro is always a problem. Dragsters use 1.2 amps in each plug. 50deg advance is
is equally or more dangerous than methanol. After combustion, the vapor contains
large amounts of nitric acid, which causes muscle reaction and prevents a person
from breathing, so gas masks are essential to survive. Nitro on
itself is not explosive.
methanol and nitro methane can have various compounds added to them.
oxide (epoxy propane) is used with nitro to increase combustion flame speed. It
can also be used with petrol and methanol to give 2-3% power gain. It must be
stored in plastic or aluminium containers because it becomes volatile when in
contact with copper or rust. Nitro propane
can be added to any fuel to increase the oxygen content. Obviously, serious
remapping must be done afterwards.
All of the
above additives must be used in specific mixes and there are a host of
precautions which must be practiced when mixing them….
There is not enough scope
here to go through the details, but like any chemicals,
you shouldn’t use them without discussing it with an experienced tuner or
World Effects of Octane Increase.
On a highly
tuned two litre turbo (Scooby, Evo, GT4) the following
can be expected. If the
engine is running at 400bhp on 98RON fuel then the use of 101 Shell clubman fuel
will bring the engine to 450bhp due to the added boost and advance allowed
because of the octane increase. With a further increase to 102 WRC fuel and the
use of toluol additive to bring the MON to 113octane, the engine will produce
just over 500bhp(at 9psi boost higher than the 98octane level).