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7.1 Flow Testing
7.1.1 Introduction
Many of the applications of flowbenches and the data they provide are often set apart from normal data
because of the mystique associated with flowbenches and flow testing.
An air flowbench is essentially a device that measures the resistance of a test piece (cylinder head,
manifold, carburetor, throttle body, exhaust systems, etc.) to flow air. Many different designs and models
are on the market today that allow the user to compare flow results before and after changes in the flow
path.
7.1.2 What Is A Flow Test?
In its simplest form, flow testing consists of blowing or sucking air through a component at a constant test
pressure. Then the flow rate is measured. A change is made and then the component is retested. Greater
airflow indicates an improvement. If the tests are made under the same conditions, no corrections for
atmospheric conditions or machine variations are required. The results may be compared directly.
For more advanced tests, it is possible to adjust and correct for all variations so test results may be
compared to those of any other device, tested under any conditions, or tested on any other SuperFlow
flowbench. Further calculations can be made to determine valve efficiency and various recommended port
lengths and cam timing on a cylinder head. Other calculations can be used on other devices.
7.1.3 Flowbench History
1
Flowbenches and airflow data have been part of the internal combustion engine development cycle for
design, research and development for many years. Some of the first engine airflow studies (using some
type of flow testing) date back to the early 1900s. However, the study of engine airflow and flowbench
information and the relationship to performance has only been commonplace in the racing industry since
the late 1960s.
The foundry process and the associated compromises actually controlled most early cylinder head and
manifold designs. These manufacturing compromises drove most designs—not the technical aspects or
specific airflow requirements.
When SuperFlow Corporation introduced the first portable flowbench to the engine builders of the world
in 1972, airflow science came to kitchen tables, shops, and garages everywhere. More elaborate and
complex benches had been around for some time when the first SuperFlow model was made available,
but never in such an easy-to-use configuration. As market demand and understanding grew, many larger
models were made available as racers everywhere began to compare flow information. Thousands of
benches are in use every day, and engine component airflow technology is growing rapidly.
The various test pressures in use in the field are interesting because they were derived as a historical
reference more than a technical requirement.
The first airflow benches in use at the Original Equipment Manufacturer (OEM) level were expensive,
cumbersome, and complex machines that were applied in the late 1960s and early 1970s for some
specific engine airflow development work. Oldsmobile and Pontiac used flowbench-guided designs
early on; however, Chevrolet did not have a flowbench lab in use until the 1970s. American Motors used
7.0 Flowbench Theory
1. Written by Harold Bettes II.
