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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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