Computech Systems RaceAir Pro User manual

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v3b
QUICK START GUIDE
1. Make sure batteries are installed.
2. Press POWER ON/OFF key.
3. Press SAMPLE key to take weather sample.
4. Use left side black and red keys to access programs. Press ALT first for red programs.
5. Use down arrow (NO) key or up arrow (YES) key to move the display left indicator
arrow to navigate program menus.
6. Press ENTER to use program.
7. Answer program questions (?) to calculate result.
CONTENTS
COMPUTER PROGRAM CAPABILITIES Page 2
GENERAL INFORMATION Page 8
Power Requirements. Page 8
Keyboard Functions. Page 8
Program Access and Use. Page 9
Communication Port. Page 9
Program Updates. Page 10
Additional Instructions Page 10
COMPETITION WEATHER ANALYZER Page 10
Overview Page 10
Weather Terms. Page 10
Good Air / Bad Air. Page 13
Sampling Information. Page 14
Calibration Page 15
Specifications Page 15
Weather Analyzer Operation. Page 15

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COMPUTER PROGRAMS OPERATION Page 16
COMPUTER PROGRAM CAPABILITIES
This list is indented to show access menu levels. See Program Access and Use on page 9.
TUNE-UP key Page 16
1 Jetting Menu
1 Holley Page 17
This program will calculate the proper Holley carburetor jet to use based
on a change in weather conditions. It also allows the user to adjust the
air/fuel ratio to achieve the proper engine tune.
2 Prec Jets Page 18
This program will calculate the proper jet diameter, in inches or millimeters,
to use based on a change in weather conditions for any carburetor. It also
allows the user to adjust the air/fuel ratio to achieve the proper engine tune.
3 Mikuni Jets Page 18
This program will calculate the proper Mikuni carburetor jet to use based
on a change in weather conditions. It also allows the user to adjust the
air/fuel ratio to achieve the proper engine tune.
4 Keihin Jets Page 19
This program will calculate the proper Keihin carburetor jet to use based
on a change in weather conditions. It also allows the user to adjust the
air/fuel ratio to achieve the proper engine tune.
5 Injection Page 19
This program will calculate the proper continuous flow mechanical fuel
injection main jet (pill) to use based on a change in weather conditions
using jet and nozzle areas. It allows the user to adjust the air/fuel ratio to
achieve the proper engine tune. Additionally, a fuel rail pressure change
is calculated for use in adjusting a high speed lean out system relief
valve. See Important program information on page 21.
6 F/G Injection Page 20
This program will calculate the proper continuous flow mechanical fuel
injection main jet (pill) to use based on a change in weather conditions
without knowing the injector nozzle sizes. It also allows the user to adjust
the air/fuel ratio to achieve the proper engine tune. Additionally, a fuel rail
pressure change is calculated for use in adjusting a high speed lean out
system relief valve. See Important program information on page 21.
7 High Speed Page 21

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This program will calculate a bypass flow jet change for a continuous flow
mechanical fuel injection high speed lean out system. See Important
program information on page 21.
8 Square Area Page 22
This program will easily calculate the area of several nozzles or jets and
provide a single orifice diameter equivalent.
2 Blower OD Page 22
This program will calculate blower drive speed in relation to crankshaft speed
based on pulley tooth count or circumference.
3 Meth. Spec. Page 23
This program is used in conjunction with a hydrometer and thermometer to correct
the specific gravity of methanol when checking for moisture contamination.
4 Gas. Spec. Page 23
This program is used in conjunction with a hydrometer and thermometer to correct
the specific gravity of gasoline.
5 Nitro % Page 23
This program is used in conjunction with a hydrometer and thermometer to
determine the corrected nitro percentage of a measured sample.
6 EGT Correct'n Page 24
This program will correct the indicated or observed engine exhaust gas
temperature (EGT) for variations in engine air inlet temperature. The corrected
EGT value can be used as a tuning aid.
7 EGT Predict'n Page 24
This program will calculate the indicated or observed engine exhaust temperature
(EGT) from a corrected EGT and the current engine air inlet temperature.
DIAL-IN key
1 Standard Page 25
This program will predict an elapsed time (ET) dial-in, for 1/8 and 1/4-mile Drag
Racing, based on 1 previous good run and the change in horsepower correction
factor due to a weather change. Note: This program requires changing the fuel
selection in SET-UP, Program Setup, Fuel Setup when using methanol.
2 Density Altd Page 26
This program will predict an elapsed time (ET) dial-in based on 3 previous good
runs and the change in density altitude due to a weather change.

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T-STOP key Page 27
This program will calculate the throttle closed timer setting to produce a desired elapsed
time (ET) based on 2 previous runs, 1 faster than the index and 1 slower than the index.
The program capacity allows data storage for 3 different cars or 3 different indexes.
DRAG FORMULAS key
1 Gear Ratio Page 29
This program will calculate the vehicle gear ratio based on tire size, MPH, engine
RPM, and torque converter slip.
2 Trap RPM Page 29
This program will calculate the trap engine RPM based on tire size, MPH, gear
ratio, and torque converter slip.
3 Converter Slip Page 30
This program will calculate the torque converter slip RPM and percentage based
on tire size, MPH, engine RPM, and gear ratio.
CIR.TRK. FORMULAS key
1 Gearing/Tires
1 Engine RPM Page 33
This program will calculate the resulting engine RPM change with tire size
and gear ratio changes.
2 Gear Ratio Page 33
This program will calculate the proper gear ratio to compensate for changes
in tire size and desired engine RPM.
3 Tire Size Page 33
This program will calculate the proper tire size to compensate for changes
in gear ratio and desired engine RPM.
4 MPH Calc Page 37
This program will calculate the vehicle MPH based on engine RPM, gear
ratio, and tire size.
5 Tire Stagger Page 34
This program will suggest a tire stagger condition based on track
measurements.
2 Chassis

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1 Setup by Pct Page 34
This program will calculate the scale weights for each wheel from total
vehicle weight and requested front, rear, and diagonal weight distribution
percentages.
2 Setup by Wgt Page 35
This program will calculate the front, rear, and diagonal weight distribution
percentages from actual scale weights for each wheel.
3 Fuel Mileage Page 35
This program will calculate fuel mileage from pit stop measurements, predict when the
next fuel stop should be made, and calculate the fuel required to finish the race.
4 Liquid Wgts Page 36
This program will calculate the weight of water, methanol, and gasoline when the
quantity in gallons is entered.
ALT - AIR CORR. key Page 16
This program will calculate the horsepower correction factor, density altitude, air density
ratio (ADR), dry barometer, wet bulb temperature, dew point, partial vapor pressure, water
vapor grains, and pressure altitude from an input of temperature, relative humidity, and
absolute barometer. Use this program to calculate weather data when taking an actual air
sample is not desired (i.e. from logbook entries of temperature, relative humidity, and
barometric pressure or evaluating other than sampled conditions).
ALT - RUN COMP key Page 30
This program will estimate the 1/8 or 1/4 mile elapsed time (ET) and MPH for a run where
thethrottlewasclosed beforethe finish line. Theprogram uses informationfroma previous
full pass to predict performance.
ALT - DRAG PERF key
1 Full Run Std Page 30
This program will correct observed finish line elapsed time (ET) and MPH
performance to Standard Day weather conditions. This information can be used to
compare runs done on different days to evaluate vehicle changes or driving
techniques.
2 Intermed. Run Page 31
This program will correct observed 60', 330', 660', 1000', and 1320' elapsed times
(ETs) to Standard Day weather conditions. This information can be used to
compare runs done on different days to evaluate vehicle changes or driving
techniques.
3 Est. 1/8 HP Page 32

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This program will estimate the horsepower output required to move the vehicle to
the 660' track marker based on vehicle weight and elapsed time (ET). It will also
adjust horsepower corrected to Standard Day weather conditions.
4 Est. 1/4 HP Page 32
This program will estimate the horsepower output required to move the vehicle to
the 1320' track marker based on vehicle weight and elapsed time (ET). It will also
calculate horsepower corrected to Standard Day weather conditions.
5 Est. ET/MPH Page 32
This program will estimate the 1/8-mile elapsed time (ET) and MPH plus the 1/4-
mile ET and MPH from engine horsepower and vehicle weight.
ALT - ENGINE FORMULAS key
1 C/R Menu
1 Calc Ratio Page 37
This program will calculate engine compression ratio from cylinder bore,
crankshaft stroke, combustion chamber volume, and piston dome volume.
Piston deck height, head gasket volume, and supercharger boost pressure
are included in the equation.
2 Calc Chamber Page 38
This program will calculate the required combustion chamber volume from
cylinder bore, crankshaft stroke, and piston dome volume when a
compression ratio is specified. Piston deck height, head gasket volume,
and supercharger boost pressure are included in the equation.
3 Calc Dome Page 38
This program will calculate the required piston dome volume from cylinder
bore, crankshaft stroke, and combustion chamber volume when a
compression ratio is specified. Piston deck height, head gasket volume,
and supercharger boost pressure are included in the equation.
4 Pour Chamber Page 39
This program will calculate the engine compression ratio using the cylinder
bore, crankshaft stroke, and the measured liquid volume poured into the
combustion chamber of an assembled engine with the piston on top dead
center (TDC).
5 Pour Dome Page 39
This program will calculate the effective piston dome volume by measuring
the piston deck height, installing a clear plastic plate in place of the cylinder
head, and then measuring the poured liquid volume in the void.

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2 C.I.D. Menu
1 Calc C.I.D. Page 40
This program will calculate engine displacement in cubic inches and liters
from cylinder bore, crankshaft stroke, and the number of cylinders.
2 Calc Bore Page 40
This program will calculate the cylinder bore required for a specified
engine displacement when crankshaft stroke and the number of cylinders
are given.
3 Calc Stroke Page 40
This program will calculate the crankshaft stroke required for a specified
engine displacement when cylinder bore and the number of cylinders are
given.
ALT - SET-UP key
1 Program Setup
1 Fuel Setup
This program is used to set the fuel type (gasoline, methanol, or special)
in the Std. Dial-In, the Full Run Std, and the Intermed. Run programs.
The default setting is gasoline. Press the down arrow key to view the
other fuels then press ENTER to select that fuel. The proper fuel factor is
automatically set into the programs when gasoline or methanol is
selected. To compensate for other fuels or to use another factor, press
the down arrow key until Special is displayed then press ENTER. The
display will show Factor?. Press in the desired multiplication factor and
press ENTER. For example, a fuel factor that is 10% less than the
standard would be 0.90.
2 T-Stop Setup
This function is discussed in the Throttle Stop program. It only needs to
be done to predict throttle stop timer settings.
3 D.A. Setup
This function is discussed in the Density Altd Dial-In program. It is used
to determine the slope of run data for that program.
4 SAE HP vs. STD
This function changes the horsepower correction method from Standard
to SAE. The default setting is STD. When the SAE HP? NO line is
displayed, press ENTER to cause the cursor block to flash then YES to
change to the new SAE correction factor.
2 Factory Setup

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1 Set Clock
This program is used to set the date and time.
2 Show Calib.
This screen is for factory use to show the weather sensors calibration file.
3 Factory Reset
This program will remove the weather sensor calibration file from the
computer memory. DO NOT use this program without specific instructions
from Computech on how to save the calibration file.
4 Empty Recycle
This program can be used when the Loading User Memory…
Message remains on the screen for several seconds. Emptying the
recycle bin will speed up the computer operation.
5 Clr User Mem
This function is not normally used. Clearing the user memory will reset all
computer variables to 0. All set-up functions will need to be reentered.
Battery=
This line indicates the measured voltage in the computer circuit. When on
battery power, it can show when the batteries are getting weak.
3 Calculator
This program is a 4 function calculator (i. e. add, subtract, multiply, and divide).
The +key (YES) and the --key (NO) are used to add and subtract. To multiply,
press ALT then + or to divide press ALT then --. Press ENTER to see the answer.
Important: The calculator can be accessed from within any program by pressing
ALT then ENTER. The calculator function will remember the number from the
computer program line where the left indicator arrow is positioned. The calculator
functions can then be used with that number. The computer will insert the new
calculated value back in the program line by pressing ALT then ENTER again.
Dynamometer Horsepower Correction
The = Sampled Wthr = screen can be used to quickly correct observed dyno torque
and horsepower values. Press the SAMPLE key and place the RaceAir Pro near the
engine air intake. Allow the unit to finish sampling. Make sure the left side indicator
arrow is on the STD Corr= (or SAE Corr=). Press ALT then ENTER to transfer the
correction factor to the calculator. Press ALT then + (to multiply). Press in the observed
number (torque or horsepower) and press ENTER to see the corrected value. Pressing
ALT ENTER again will send the computer back to the = Sampled Wthr = screen. The
process can be repeated again for the next value. The same technique can be used for
previously recorded weather conditions using the AIR CORR. program.

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GENERAL INFORMATION
Power Requirements.
The RaceAir Pro uses 6 AA batteries. Note the polarity markings on the battery tray when
installing the batteries. The unit will automatically turn off after 10 minutes of inactivity. The
highest current draw on the batteries is the fan that comes on when the air SAMPLE key is
pressed. Use the display LIGHT only as necessary, to preserve battery life. The computer will
display a caution message when the battery voltage is too low for acceptable operation. If the
display stops responding to keystrokes, including the POWER ON/OFF key, it may be necessary
to remove and reinstall the batteries to restart the computer.
The computer may also be powered with a 12-V dc adapter through the upper connector provided
on the left side of the case. The 110-V ac to 12-V dc adapter is available from Computech
Systems, Inc. The unit may be safely powered by the adapter while the batteries are installed.
Keyboard Functions.
The keyboard has several multifunction keys. The YES key also functions as an up arrow key and
a + (plus) key. The NO key functions as a down arrow key and a -- (minus) key. To enter a
negative number into a program, press the number, press the minus key, then press ENTER. The
split black and red keys have 2 functions. When a black and red key is pressed the computer will
go to the function labeled in black. When the red ALT key is pressed then a black and red key is
pressed the computer will go to the function labeled in red.
The POWER ON/OFF key must be pressed and momentarily held to turn on the computer.
The ENTER key is discussed in Program Access and Use below.
The CLEAR key may be used anytime to exit a menu or program. CLEAR is also used to
backspace an incorrect entry.
When the computer is powered, pressing the red SAMPLE key will turn on the fan and take a
weather sample. The weather sampling process may be aborted by pressing SAMPLE again.
Several of the included programs use weather information in the calculations. When a program
asks for current weather information, pressing the IMPORT WEATHER DATA key will
automatically transfer that data. The RaceAir Pro powers up in the ==Live== Fan OFF mode. The
actual air data from the last sample may be viewed by pressing ALT then IMPORT WEATHER
DATA.
Program Access and Use
The COMPUTER PROGRAM CAPABILITIES list can be used to select a program. The list is
indented to show the access menu levels. The indicator arrow on the left side of the display may

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be repositioned in a menu or in a program screen by pressing the up or down arrow keys. The up
and down arrow keys will repeat or continue to move the indicator arrow when held. Pressing the
ENTER key will make the computer go to the item where the left indicator arrow is positioned.
An alternate quick program access method is to use the number shown to the left of a program.
For example - to access the Holley carburetor jetting program, press TUNE-UP, then 1 to access
the Jetting Menu, then 1 again to get to the Holley program.
When a program needs a user input a ? will appear at the end of a statement. A number from the
computer memory may appear after the ?. Either accept this number by pressing ENTER or press
in a new number on the keyboard then press ENTER. When an answer is presented, an = will
appear at the end of the statement. A blinking cursor block will appear on the right side of a
statement when the computer is expecting a user input.
Recalculate Function. The up and down arrow keys may be used to reposition the left side
indicator arrow to a program input line. Pressing ENTER will open that input and show a blinking
cursor block to accept a new entry. It is not necessary to restart the program from the beginning
to calculate a new answer.
Communication Port.
The lower of the 2 ports on the left side of the computer is for communication with a personal
computer (PC). The optionally available Computech Weather Pro software will interface with the
RaceAir Pro. When the communications link is established, the sensors in the RaceAir Pro send
information to the PC that is running the Weather Pro program. The Weather Pro calculates the
various air conditions, logs the information, and presents a graphic view of what the weather is
doing. A weather file is saved for future reference. The Weather Pro software, with the required
cables and power supply, is available from Computech Systems, Inc.
Additionally, the Comm port is used to update the RaceAir Pro program firmware. An interface
kit is available from Computech Systems, Inc. to perform these updates. The kit contains the PC
interface software, the PC to RaceAir Pro interface cable with serial adapter, and a power
supply.
Program Updates.
The RaceAir Pro program firmware is user updateable with the optional PC interface kit. The
latest version of the program will be posted on the Computech Systems, Inc. web site.
Downloads are free for the life of the computer. As changes or additions are made to the
program, new files will be posted on the web site. The RaceAir Pro may be sent back to
Computech Systems, Inc. for program updates, if desired.

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COMPETITION WEATHER ANALYZER
Overview
The weather analyzer contained in the RaceAir Pro measures the air quality. It is based on the
air temperature in degrees Fahrenheit (F), the relative humidity in percent (%), and the absolute
barometric pressure in inches of mercury (Inches Hg). Subtle changes in any of these variables
can have an impact on the performance of your vehicle. This portion of the RaceAir Pro will
provide you with: the STD or SAE HP Correction Factor, Density Altitude (ft), Air Density Ratio
(%), Dry Barometer pressure (Inches Hg), Dew Point temperature (F), Wet Bulb Temperature
(F), water Vapor Pressure (Inches Hg), and Pressure Altitude (ft).
Weather Terms. This list is in alphabetical order.
Air Density Ratio
Air density ratio (ADR) is the ratio produced by dividing the calculated density of the air
being sampled by the Standard Day air density. Standard Day air is defined as a
temperature of 60F, a relative humidity of 0%, and an absolute barometric pressure of
29.92 In. Hg. The ADR for those conditions is 1.00. The RaceAir Pro expresses this ratio
as a percent, Standard Day = 100%, as an aid to understanding the performance
increases and decreases that air density causes. Air Density Ratio is used to determine
engine fuel tuning changes. If the ADR goes down 2%, then fuel must be reduced 2% to
stay at the same air/fuel ratio.
Absolute Barometric Pressure
Absolute barometric pressure, measured in inches of mercury (Inches Hg), is the pressure
that is present at the location of the sensor from the atmosphere. The term ‘barometric’
comes from the weather instrument, the mercury barometer, which is used as a laboratory
precision measuring device. The term ‘absolute’ refers to absolute zero, where without the
earth’s atmosphere, the measured pressure would be 0 Inches Hg. Normal pressure
gages have a scale that sets the atmospheric pressure of 14.7 pounds per square inch
(29.92 Inches Hg) as the zero point. This is referred to as gage pressure. The RaceAir Pro
provides the absolute barometric pressure that is used in the calculations for ADR, Density
Altitude, and the Correction Factor. It has the biggest influence on air quality. Absolute
barometric pressure normally varies between 25 and 31 Inches Hg depending on the
elevation above sea level where the sensor is. The atmospheric pressure defined as
Standard Day at sea level is 29.92 Inches Hg and decreases about 1 Inch Hg per 1000 ft.
of elevation.
Altitude
Altitude is the elevation above mean sea level (MSL) in feet.
Altitude – Density
See ‘Density Altitude’.

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Altitude – Pressure
See ‘Pressure Altitude’.
Barometric Pressure - Absolute
See ‘Absolute Barometric Pressure’.
Barometric Pressure - Corrected to Sea Level
In order to provide a standard method of stating barometric pressure, the National
Weather Service (NWS) adjusts the absolute barometric pressure observations to sea
level elevation (0 feet). Without this standard the barometer readings would be
meaningless at different geographic elevations around the world. The correction adds
about 0.001 Inches Hg per foot of elevation to the absolute barometric pressure number.
Corrected barometric pressure cannot be used for performance calculations without
subtracting the local elevation from the NWS value. Even then it would be an
approximation because the barometer is at another location.
Barometric Pressure - Dry
See ‘Dry Barometric Pressure’.
Correction Factor
The correction factor is a Society of Automotive Engineers (SAE) equation that uses the
calculated dry barometric pressure and the measured local temperature to compensate
for changes in dynamometer observed horsepower readings due to air density differences.
This method allows performance comparison of observed readings taken on different days
or in different parts of the world. The correction factor can also be applied to track
performance. There are 2 correction factor equations in common use in the industry - the
current SAE and STD or the old SAE standard. The STD and SAE methods also have
different reference points (where correction factor 1.000 occurs). Therefore, values
corrected with one method cannot be compared to values corrected by the other.
Density Altitude
Density altitude is a value in feet that relates the local measured atmospheric conditions
(absolute barometric pressure or pressure altitude, temperature, and relative humidity) to
the aeronautical industry defined standard day atmosphere. The density altitude for an
absolute barometric pressure of 29.92 Inches Hg or a pressure altitude of 0 ft, a
temperature of 60F, and a humidity of 0% is 0 ft. A good air day in the spring or fall might
be below 0 ft (i.e. –831 ft). Conversely, a hot summer day might have a density altitude of
4500 ft. (equivalent to 4500 ft of altitude on a standard day).
Dew Point
The dew point temperature is the calculated temperature at which the measured partial
saturation of water vapor in the air will turn to liquid and form dew. Moisture can cause
inconsistent traction and, in certain circumstances, effect engine performance. The
warmer the air is the more water vapor it can hold. See ‘Relative Humidity’ for more
information. An air sample has a specific amount of water vapor present. As the
temperature drops and reaches the dew point, the air can no longer hold the water vapor
suspended so it condenses and turns to water. This condensation will occur on cooler
surfaces first. Computech research with methanol fuel, and to a lesser extent with

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gasoline, has shown that when the ambient temperature falls to within 5 to 10F of the
dew point temperature there will be an unexpected slight fall off in performance due
primarily to fuel degradation in the intake manifold that is caused by water contamination.
By keeping accurate records as to when the performance actually falls off in relation the
outside temperature versus the dew point temperature, performance degradation can be
predicted.
Dry Barometric Pressure
The dry barometric pressure (Inches Hg) is the absolute barometric pressure with the
partial saturation water vapor pressure from humidity subtracted. The measured absolute
barometric pressure is from a combination of oxygen, nitrogen, argon, and some other
trace gases plus water vapor. The portion of the air that is water vapor will not contribute
to combustion of the fuel and therefore must be factored out. Dry barometric pressure is
used to calculate ADR, Density Altitude, and the Correction Factor.
Dry Bulb Temperature
See ‘Temperature’.
Pressure Altitude
Pressure altitude is the aircraft altimeter indicated value in feet that results from setting
the pressure adjustment window to 29.92 Inches Hg. This number relates to the
aeronautical industry defined Standard Day altitude. An indication of 0 ft is equal to an
absolute barometric pressure of 29.92 Inches Hg. Lower or negative values (i.e. –180 ft)
indicate more air pressure. Higher values (i.e. 2500 ft) show less air pressure. An altimeter
will also show absolute barometric pressure (Inches Hg) in the pressure window when the
altitude pointer is rotated to indicate 0 ft. Note that this number is pressure only. Until it is
adjusted for temperature and humidity via the density altitude process it is not an indication
of total air quality.
Relative Humidity
Relative humidity (% RH) is a value to indicate how much water vapor is present in an air
sample. Air has the ability to hold more water vapor as the temperature increases. This
phenomenon makes comprehending water vapor content difficult. By always relating the
amount of water vapor present to the maximum amount that air could hold at that
temperature, the relationship is easier to understand (i.e. 50% RH is always 50% of the
possible saturated water vapor content for air at any temperature).
Temperature
Temperature (F) is also referred to as dry bulb temperature. In order to correctly calculate
the effect of temperature on performance, the measured temperature needs to be similar
to the engine intake air temperature.
Vapor Pressure
Vapor pressure (Inches Hg) is a value calculated from the sensed temperature and relative
humidity. The RaceAir Pro uses numbers derived from mechanical engineering steam
tables to calculate the partial saturation vapor pressure of the moisture in the sampled air.
That value is displayed and used in the ‘Dry Barometric Pressure’ computation. The vapor
pressure number indicates the portion of air pressure that is actually from water vapor

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and, of course, will not support combustion.
Water Vapor
Water vapor (grains, Gr) is the same information as ‘Vapor Pressure’ expressed in
different units. Some race teams use 100 Gr as the threshold for making water vapor
related tuning changes. Engine fuel flow and ignition timing may need to be increased
above the threshold.
Wet Bulb Temperature
Wet bulb temperature refers to using an expanding liquid type thermometer with a water
soaked cotton wick over the sensing bulb. This technique produces a lower temperature
indication for lower humidity conditions due to evaporation. The wet bulb temperature and
the dry bulb temperature can be used to calculate ‘Relative Humidity’.
Good Air / Bad Air.
The atmospheric conditions that make air quality better for racing are: lower temperature, lower
humidity, and higher air pressure. Conditions that make the air worse for racing purposes are:
higher temperature, higher humidity, and lower air pressure. Lower Correction Factor numbers,
lower Density Altitude numbers and higher Air Density Ratio numbers all mean better air quality.
The variables that cause the Correction Factor and the Density Altitude to decrease (smaller
numerically), as well as the Air Density Ratio to increase (larger numerically), are: a lower
temperature, a lower relative humidity, a higher barometric pressure (as measured with a
barometer), or a lower pressure altitude (as measured with an altimeter). Typically, the STD
Correction Factor will be between .98 (better) and 1.15 (worse); the Density Altitude will be
between -300 ft. (better) and 8,000 ft. (worse); the Air Density Ratio will be between 85% (worse)
and 103% (better).
Atmospheric changes can be experienced when going from track to track or from Spring to
Summer to Fall at the same track. The typical change in air quality from the heat of the day to the
cool of the night is usually not very large. However, the RaceAir Pro will compensate for changes
in all of the weather variables, no matter how small.
Remember, as the Correction Factor and the Density Altitude increase (larger numerically),
performance will decrease. As the Correction Factor and Density Altitude decrease (smaller
numerically), performance will increase. The lower the Air Density Ratio (smaller numerically),
the leaner the jetting needs to be and the higher the Air Density Ratio (larger numerically), the
richer the jetting needs to be.
Sampling Information.
The top portion of the RaceAir Pro, where the red stripe is, contains the weather sensors. During
the sampling process, air is drawn in through the diagonal slits in the faceplate by the internal fan.
The air is then exhausted through the vents on the upper left side of the case. These air passages

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must remain clear for accurate measurements. Also, the temperature, humidity, and pressure
readings may not be accurate when the fan is not operating.
When the SAMPLE key is pressed, the RaceAir Pro automatically samples current weather
conditions, locks in a set of good sample readings, and then displays those readings along with
a number of calculated weather values. These values may be used independently, or in
conjunction with the programs contained within the RaceAir Pro computer for accurate
performance prediction and tuning assistance.
Important: Air samples should be taken at approximately engine air intake height above the same
type of surface as the racetrack (i.e. dirt, asphalt, or concrete). Keep the unit out of direct sun and
away from engine exhaust or other heat sources while sampling. Also, keep your body heat away
from the intake vents on the front. Use the RaceAir Pro the same way each time an air sample is
taken. When in use, keep the RaceAir Pro in an environment similar to that being sampled. For
example, don’t pull the RaceAir Pro directly out of a hot trailer and immediately take a sample.
The amount of time required for such a sample to stabilize is significantly longer than normal and
the result could be less accurate. The sampling process will typically take between 15 seconds to
3 minutes.
Don't allow water to enter the vents in the front or on the left side. If this happens or if the display
appears confused, remove the batteries and allow the RaceAir Pro to dry out!
Calibration
Each RaceAir Pro goes through a rigorous calibration process to assure the highest accuracy of
the readings. The calibration data is unique to each unit. The data is stored in the computer
memory with an internal battery backup so the weather sensor corrections are not lost during
battery changes. Under normal operating and storage conditions, it is not necessary to have the
unit periodically recalibrated.
Specifications
Display Resolution: Temperature: 0.1 degree F
Relative Humidity: 1%
Absolute Barometric Pressure: 0.01 Inches of Mercury
Internal Resolution: Temperature: 0.01 degree F
Relative Humidity: 0.1%
Absolute Barometric Pressure: 0.003 Inches of Mercury
Accuracy: Temperature: +/- 1.2 degree F
Relative Humidity: +/- 3%;
Absolute Barometric Pressure: +/- 0.05 Inches of Mercury
Repeatability: Approximately equal to display resolution
Weather Analyzer Operation.

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Press and momentarily hold the POWER ON/OFF key. The computer will power up, show the
firmware version, and go to the ==Live== Fan OFF screen. When the fan is not operating, the
sensor readings will not be accurate. Press the SAMPLE key. The display will read
= Sampling… = until the sensor readings are stabilized - this may take a couple of minutes. Then
the display will read = Sampled Wthr = when the sensors have correctly measured an air sample.
Display Example: (use down arrow key to reveal more data)
= Sampled Wthr =
72.3 32 % 29.40" (temp  F humidity % barometric pressure Inches Hg)
Apr15 11:59:59pm (date and time)
STD Corr=1.0389 (HP correction factor selected: STD or SAE)
Dens Altd= 1686 (density altitude ft)
ADR= 95.2 (air density ratio %)
DryBaro= 29.139 (dry barometric pressure Inches Hg)
Dew Point= 40.7 (dew point temp  F)
Wet Bulb= 56 (wet bulb temp  F)
Vpr Prs= 0.257" (water vapor pressure Inches Hg)
Wtr Vpr=38.47Gr (water vapor grains)
Press Alt= 489 (pressure altitude ft)
The RaceAir Pro will put the current weather data in memory for automatic transfer into any of the
programs that use weather information. The air sample data will be lost if the unit is turned off.
The unit will also automatically turn off after 10 minutes of inactivity thereby loosing the air sample
data. Keeping a logbook record of run information and applicable weather information is
recommended.
COMPUTER PROGRAMS OPERATION
Air Correction Program.
This program is used to calculate weather data from keyboard entries of temperature, relative
humidity, and barometric pressure. Press ALT then AIR CORR. to start this program.
Display Example:
=== Air Corr ===
Temp? 71.0 (Enter temp  F)
Humidity? 31 (Enter humidity %)
AbsBaro? 30.24 (Enter barometric pressure Inches Hg)
STD Corr= 1.0079 (HP correction factor selected: STD or SAE)
Dens Altd= 630 (density altitude ft)
ADR= 98.2 (air density ratio %)
DryBaro= 30.000 (dry barometric pressure Inches Hg)
Dew Point= 39.1 (dew point temp  F)
Wet Bulb= 54 (wet bulb temp  F)
Vpr Prs= 0.241" (water vapor pressure Inches Hg)

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Wtr Vpr= 36.03Gr (water vapor grains)
Press Alt= -294 (pressure altitude ft)
Tune-Up Information.
In order to use any of the RaceAir Pro jetting programs a baseline tune up, which includes a
baseline air density ratio (ADR) and a baseline jet, must be established. Once the baseline tune
up is established for a particular engine combination, the jet change programs will compute a
change in the carburetor jets or the fuel injection bypass jet (pill) based on an air density change.
The lower the air density is - the leaner the engine needs to be. The higher the air density is - the
richer the engine needs to be.
CAUTION: When making any jet change, always monitor the engine exhaust gas
temperature (EGT) indications, oxygen sensor (O2) readings, air/fuel ratio indication, etc.,
- most importantly, take spark plug readings to make sure the air/fuel mixture ratio does
not become too lean. Severe engine damage can be caused by excessively lean mixtures.
Important: All the Computech Tune-Up Jetting programs require the use of flow tested jets.
Modified jets or jets that are not flow tested do not have adequate fuel metering control for use
with these programs.
To establish a baseline tune up, operate the engine at full throttle in typical racing conditions.
Record the jet size (or sizes) used, the ADR, and any pertinent time or speed information. Now,
lean the jet (or jets) down one size, make another full throttle run and repeat the process of
recording the jet (or jets) size, ADR, plus time and/or speed information. Inspect the spark plugs,
exhaust ports, etc. carefully for signs of detonation or other indications that the air/fuel mixture
ratio may be too lean. Assuming there are no signs of being too lean and the vehicle picked up
performance on the last run, repeat the entire procedure again with the jet (or jets) one size leaner.
Continue testing until the time and/or speed slows down or the engine shows signs of the air/fuel
mixture ratio being too lean. At that point, richen the jet (or jets) 1 size when tuning for peak
performance or 2 sizes when tuning for ET classes (bracket racing). The jet (or jets) and the ADR
that you have at that time is the baseline tune up. Record the baseline tune up information for
future reference.
All the Tune-Up Jetting programs provide jet suggestions that are more accurate than the jet size
increments available. This is done so the user can easily see the exact fuel requirement for the
measured ADR change from the baseline ADR. Select the actual jet closest to the suggested jet
size while being careful not to run the engine overly lean - round the number up for carbureted
applications or round the number down for fuel injection bypass systems.
TUNE-UP ADJUST. Anytime the tune up is slightly rich or slightly lean, the Adjust % line can be
used in any of the jetting programs to make adjustments to the tune up by changing engine fuel
flow a few percent at a time. When the Adjust %? cursor block is flashing, press a number key
corresponding to the desired engine fuel flow percent change (plus for richer, minus for leaner).
For example, press 2 then ENTER for a 2% richer engine fuel flow or 2 then -- (NO key) then
ENTER for a 2% (-2) leaner engine fuel flow. This tuning function can also be used when
compensating for changes in the engine or vehicle combination, such as ignition timing, camshaft,

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carburetor, headers, fuel injection pump, fuel, etc.
Holley Jets.
Read the Tune-Up Information section before using this program. The Holley Jet change
program is designed to work with Holley carburetor jets from #50 through #100. The program
utilizes actual jet flows as opposed to drill sizes when making the computations. Use this program
with the baseline tune up information to predict the proper jet to use as the ADR changes.
Important: Use only unmodified Holley flowed jets with this program. The Holley Jet program will
not make accurate predictions for methanol or nitromethane fuels. The Precision Jet program can
be used for carburetors with a single orifice main metering system using other than gasoline fuel.
Press the SAMPLE key and allow the weather analyzer to stabilize on the = Sampled Wthr =
screen. Press TUNE-UP then Jetting Menu then Holley to start this program.
Display Example:
== Holley Jet ==
Base ADR? 95.7 (Enter ADR from baseline tune up)
New ADR? 99.2 (Press IMPORT WEATHER DATA to import ADR)
Base Jet? 88.0 (Press in baseline tune up jet number)
Adjust %? 0.0 (Enter tune up change, if needed. See TUNE-UP ADJUST,
page 17.)
New Jet#= 89.1 (Calculated new jet number)
Different size primary and secondary jets or staggered jet sizes can be quickly checked by using
the Recalculate Function. See the Program Access and Use section for details.
Precision Jets.
Read the Tune-Up Information section before using this program. The Precision Jet program is
designed to work with precision drilled/reamed and flowed jets. Hand drilled jets are not accurate
enough for precise fuel metering. This program is designed to accept carburetor jet diameter in
inches or millimeters. Make sure to enter the decimal point and zeros to denote the diameter
dimension. It will work with any fuel. Use this program with the baseline tune up information to
predict the proper jet to use as the ADR changes.
Press the SAMPLE key and allow the weather analyzer to stabilize on the = Sampled Wthr =
screen. Press TUNE-UP then Jetting Menu then select Prec Jets to start this program.
Display Example:
== Prec. Jet ==
Base ADR? 95.7 (Enter ADR from baseline tune up)
New ADR? 99.2 (Press IMPORT WEATHER DATA to import ADR)
Base Dia? 0.032 (Press in baseline tune up jet size)
Adjust %? 0.0 (Enter tune up change, if needed. See TUNE-UP ADJUST,
page 17.)

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New Dia= 0.033 (Calculated new jet size)
Mikuni Jets.
Read the Tune-Up Information section before using this program. This program is designed to
accept Mikuni carburetor jet numbers. Use this program with the baseline tune up information to
predict the proper jet to use as the ADR changes.
Press the SAMPLE key and allow the weather analyzer to stabilize on the = Sampled Wthr =
screen. Press TUNE-UP then Jetting Menu then select Mikuni Jets to start this program.
Display Example:
== Mikuni Jet ==
Base ADR? 95.7 (Enter ADR from baseline tune up)
New ADR? 99.2 (Press IMPORT WEATHER DATA import ADR)
Base Jet? 150 (Press in baseline tune up jet size)
Adjust %? 0.0 (Enter tune up change, if needed. See TUNE-UP ADJUST,
page 17.)
New Jet= 155.3 (Calculated new jet size)
Keihin Jets.
Read the Tune-Up Information section before using this program. This program is designed to
accept Keihin carburetor jet numbers. Use this program with the baseline tune up information to
predict the proper jet to use as the ADR changes.
Press the SAMPLE key and allow the weather analyzer to stabilize on the = Sampled Wthr =
screen. Press TUNE-UP then Jetting Menu then select Keihin Jets to start this program.
Display Example:
== Keihin Jet ==
Base ADR? 95.7 (Enter ADR from baseline tune up)
New ADR? 99.2 (Press IMPORT WEATHER DATA to import ADR)
Base Jet? 150 (Press in baseline tune up jet size)
Adjust %? 0.0 (Enter tune up change, if needed. See TUNE-UP ADJUST,
page 17.)
New Jet= 152.6 (Calculated new jet size)
Fuel Injection Jets, Area Method.
Read the Tune-Up Information section before using this program. This program is designed to
work with mechanical fuel injection systems. The first time this program is used, all the engine
fuel nozzle sizes must be entered in the setup. When the setup is completed, the computer will
remember the total nozzle area for future calculations. This program and the Fuel Injection, High
Speed Bypass Adjust program use the same total nozzle area number from computer memory.
Use this program with the baseline tune up information to predict the proper jet to use as the ADR
changes.

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Use the following chart as an aid in determining nozzle diameter for various nozzle types.
Important: If the fuel system has a fuel pump loop with
a bypass jet or a second fixed main bypass jet circuit,
that orifice size must be included in the total nozzle
area calculations in order to produce an accurate main
bypass jet prediction.
When the setup is completed, the computer will
remember the total nozzle area for future calculations.
Record the calculated total nozzle area with other fuel
system information for future reference. When using
the Select Jet program, always check that the Area=
number matches the recorded number.
This program and the Fuel Injection, High Speed
Bypass Adjust program use the same total nozzle
area number from computer memory.
Press the SAMPLE key and allow the weather analyzer
to stabilize on the = Sampled Wthr = screen. Press
TUNE-UP then Jetting Menu then select Injection to
start this program.
Setup Display Example:
== Calc Area == (Nozzle area setup routine)
# Orifices? 8 (Enter number of nozzles of this size)
Diameter? 0.052 (Enter nozzle diameter in inches)
More? Yes (Press ENTER to input more nozzles, NO to stop)
# Orifices? 2 (Enter number of nozzles of this size)
Diameter? 0.020 (Enter nozzle diameter in inches)
More? No (Press NO to stop)
== Total Area == (Total nozzle area screen)
Area= 0.017618 (Total nozzle area in square inches, RECORD this)
Orifices= 10 (Number of nozzles)
Equiv Dia= 0.150 (Single orifice diameter equivalent in inches)
(Setup complete, press ENTER to continue)
Injection Display Example:
Approx
Crower/
Diameter
Kinsler
Hilborn
Enderle
0.016
E-165
4
16
0.017
F-200
5
17
0.020
G-240
6
20
0.022
H-280
7
21
0.023
J-320
8
22
0.024
K-360
9
24
0.025
L-390
*
25
0.026
M-410
10
26
0.028
N-470
*
28
0.029
P-510
12
29
0.030
P-550
14
31
0.032
R-620
16
32
0.034
S-710
18
33
0.035
T-740
*
35
0.036
T-792
20
*
0.036
U-800
*
36
0.037
V-840
22
37
0.038
W-880
24
38
0.039
X-930
27
39