42 — H
OT
R
OD
C
ALC
™
Calculating Carburetor Size
With a Known Volumetric Ef
fi
ciency
Building off of the previous example, you want to calculate your user-
defined carburetor size based on a known VE value. Suppose through
your experience and knowledge of your 1968 Pontiac GTO’s engine
specs and modifications, you know you can reach a VE of 95%.
KEYSTROKES DISPLAY
1. Calculate a carburetor size based on a user-specified VE. Your
RPM and engine displacement are in memory, so you need to
only add your user-specified VE of 95%:
EFF% S 95. VOL %
2. Calculate the carburetor sizes:
USER CARB SIZE 593.75 CFM
THEOR CARB SIZE 625. CFM
STREET CARB SIZE 531.25 CFM
RACE CARB SIZE 687.5 CFM
Notice within the
outputs, the User carburetor size appears
first in the output. This carburetor size is calculated using the
entered VE value of 95%. As previously mentioned, you are not
likely to find an exact size of 594-cfm.
Repeated presses of
will toggle back through the inputs and
outputs, starting with the VE input.
Calculating Volumetric Ef
fi
ciency
Volumetric Efficiency (VE) is the actual measured airflow capacity
at a particular RPM divided by the theoretical airflow capacity at
the same RPM. VE is generally expressed as a percentage. To
calculate the VE of your vehicle, you need to know a few things.
First, you need to know your actual measured airflow capacity at
maximum speed or maximum torque (a local dyno shop can help
Summary of Contents for Hot Rod Calc 8703
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