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Terms
&
Definitions |
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- Motor
Octane
(MON):
- (a)
CFR
Tested @
900 RPMs,
timing
is
varied
with
compression
ratio,
fuel is
preheated
to 300
degrees
Fahrenheit,
intake
air is
preheated
to 100
degrees
Fahrenheit.
(b)
Motor
Octane,
measured
under
varying
load is
definitely
the most
representative
octane
measurement
for Real
World
Hi-Performance
Engine
Applications.
(c)
The
closer
the
Motor
Octane
number
to the
Research
Octane
number
the more
stable
the fuel
is
throughout
the RPM
range (see
the
Octane
Differential
in the
chart
above).
This is
very
critical
when
running
higher
that
7500+
RPMs
engine
speed.
-
- R+M
Octane
(R+M):
- (a)
This
method
of
measurement
consists
of
adding
together
both the
motor
and
research
octane
numbers
and then
dividing
by two. (b)
This is
the
number
in that
yellow
box that
you see
on the
gas
pumps. (c)
This
number
should
only be
used
when
determining
which
fuel to
use in
your
street
car or
tow
vehicle.
This
method
is NOT
intended
for
correct
use in
your
racing
engine.
-
- Research
Octane
(RON):
- (a)
CFR
tested @
600 RPMs,
fixed
timing
at 13
degrees
BTDC,
fuel
temp is
not
controlled
and
intake
air is
varied
with the
barometric
pressure.
(b)
This is
basically
a
No-Load
test and
this
number
should
never be
used to
determine
which
fuel to
use in
your
race
engine.
-
- Specific
Gravity
(SG):
- (a)
This
is the
weight
of fuel
compared
to
water,
water
being at
1.00. If
race
fuel is
.750
(specific
gravity)
it would
weigh ¾
the
weight
of
water.
If water
at 60
degrees
Fahrenheit
weighs
8.125
pounds
per
gallon (ppg),
then
race
fuel at
.750
will
weigh
6.09 (ppg).
(b)
The less
dense
the fuel
(lower
specific
gravity)
the
higher
the BTU
content
and the
better
the
stability
of the
fuel at
higher
RPMs. (c)
The
lower
the
specific
gravity
of the
fuel,
the more
crucial
the
jetting
becomes,
and the
easier
it is to
run the
engine
lean,
possible
causing
internal
damage. (d)
The
combustion
speed is
determined
primarily
by the
pressure
(density)
of the
fuel
mixture.
-
- Lead
Content
(LC):
- (a)
When
lead is
added to
fuel,
the
knock
resistance
(anti-knock
value)
is
increased.
Lead is
also
used to
increase
the
octane
to a
higher
number.
-
- Consistency:
- It
is very
important
that the
fuel you
use
maintains
it's
purity
and
consistency
regardless
of which
brand
fuel you
use. Try
NOT
to
purchase
fuel
that has
been
stored
in bulk
storage
tank, or
transferred
from one
bulk
location
to
another.
Bulk
fuel
storage
tanks
have a
tendency
to sweat
or
secrete
moisture,
therefore
changing
the
consistency
or
purity
of the
fuel. If
at all
possible
buy your
fuel in
a
factory
sealed
drum
(the
cost is
usually
higher)
but it
is well
worth it
in the
long
run.
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