User guide

42 — HOT ROD CALC™
Calculating Carburetor Size
With a Known Volumetric Efficiency
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 Efficiency
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