05-12
MMC2005-001_05A.FM
SECTION 05 - ENGINE PREPARATION
Jetting, horsepower, and B.S.F.C. data can be ob-
tained with dyno testing but also confirmed with
field testing. The tried and true method of deter-
mining mixture ratio is to inspect the parts of the
engine that are directly exposed to the combus-
tion process. The two best indicators are the spark
plug and the piston dome. The color and where it
is located are the two things to look for. Chocolate
brown on the insulator, ground electrode, and pis-
ton dome indicate a proper mixture. The ground
electrode should show a difference in color just at
the radius of the electrode.
The engine must be operated under load for at
least one minute to obtain accurate readings.
Establish the C.R.A.D. by using the following for-
mula:
C.A.P. = Corrected air pressure
C.A.P. = B - E
B = Barometric pressure readings (in – Hg)
See saturation pressure (chart 1).
S.P. = Saturation pressure (in – Hg)
R.H. = Relative humidity (%)
Record the C.R.A.D. when correct jetting has been
established. This is your base line for future use.
Example: Testing established a 400 main jet at
C.R.A.D. of 100%. One week later, the C.R.A.D.
at the track is 110%. Use the following formula to
establish the new main jet.
New main jet = 440
Record the C.R.A.D. when correct jetting has
been established. This is the baseline for future
use. Jetting corrections for a different C.R.A.D.
can be obtained with the following ratio:
Example: Testing results in a 570 M.J. at a C.R.A.D.
of 105.4%. Two weeks later at the race track, the
C.R.A.D. is 110.9%.
The new M.J. =
New M.J. = 600
Useful Equations
C.F. =
C.A.P. = B – E
C.R.A.D. =
Where:
B = barometer reading (in-Hg)
E = vapor pressure (in – Hg) = S.P. ×
or use wet bulb/dry
bulb temperature and
psychrometric chart
T = carb. inlet air temp (°F)
S.P. = saturation pressure (in-Hg)
R.H. = relative humidity (%)
C.A.P. corrected air pressure (in-Hg)
C.HP = Corrected brake horsepower
B.S.F.C. = Brake specific fuel consumption
C.R.A.D. = Corrected relative air density (%)
E.G.T. = Exhaust gas temperature
W.O.T. = Wide open throttle
C.R.A.D.
1737,97 x C.A.P.
460
T
+
-----------------------------------------------------
=
E
Vapor pressure
S.P. x
R.H.
100
------------
⎝
⎠
⎛
⎞
=
=
New
main jet
New C.R.A.D.
Baseline main jet
×
Base line C.R.A.D.
------------------------------------------------------------------------------------------
=
Example:
110
400
×
100
---------------------------
New
main jet
New C.R.A.D.
Base line M.J.
×
Base line C.R.A.D.
----------------------------------------------------------------------------------
=
110.9
570
×
105.4
--------------------------------
29.92
B
E
–
---------------
460
T
+
520
-------------------
×
1737.97
C.A.P.
×
460
T
+
---------------------------------------------
R.H.
100
-----------
Содержание ski-doo MACH Z 1000 SDI
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