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Useful Flowbench Tools

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. Engine component airflow data is easy to compare if you know how. Here are tools we recommend using to make the job of testing airflow easier and much more fun than makeshift approaches.

Magic Wand

It provides an indication of activity and direction of flow inside a port or device under test. The magic wand is made from a 1/16” diameter welding rod that is 12” long. The welding rod has a small round ball on the end – from placing the road in a molten pool of metal – and a piece of dacron or nylon type kite string glued to itself to form a little flag about 3/8” long. This is a good flow visualization indicator.

Pilot Tube

It provides a way to probe the port to supply local velocity numbers. It can be used with SuperFlow’s FlowCom, pressure manometer, or special port software to plot areas of activity in the airstream in a port. It’s difficult to use in very small ports. It requires one type for exhaust use and a different one for intake use.

Flow Ball

It provides a method to probe a port and verify if flow is attached or separated at some point in the port. Flow balls are made by tack welding various diameters of ball bearings to a 1/16” diameter welding rod that 12” long. Flow balls typically start with 1/8” diameter and go to ½” diameter in 1/16” increments. These tools are an easy way to find problem areas in the port without great difficulty. It’s very effective in evaluating the short-turn radius in a port of where a wall has a directional change.

Port Molding Rubber

It provides an easy way to look at a port. The mold is made of silicone-based material (a two-part process) that is poured into the port with value in place. After it sets, it can be removed in one piece. The mold can be sliced and the cross-sectional profile drawn on graph paper to help measure the area at different locations in the port.

Graph Paper

This creates an easy way to measure the cross-sectional area in a port. The paper cutouts are trimmed to fit different places in the port, and the squares can be counted, providing an accurate way of measuring the area.

Poster Board

This creates an easy way to make patterns to help the developer reproduce the same port shape and size. The poster board can then be used to trace patterns in aluminum or plastic that provides benchmarks for the developer to use in duplicating an established shape in other ports and cylinder heads of the same type.

Radius Inlet Guide

It provides a smooth approach to the port or device being tested and is intended to decrease the “edge effect” at the port flange. The radius used should be as large as possible and at least ½” radius. The thickness of the inlet guide should be at least 50% of the height of the port. The size outside the port cross section should also be least 50% of the height of the port so all directions have a smooth approach. It is not uncommon for the inlet guide to improve the flow from 6% to 10% over no guide in use.

Exhaust Pipe

All testing of the exhaust side of the cylinder head should use a short section of exhaust pipe that is at least the diameter of the port. The appropriate length is about 10” to 12” long.

Bore Simulation Adapter

All flow testing of cylinder heads should use an adapter that simulates the bore size within 1/16” of the diameter used on the engine. The length of the simulated bore should be at least equal to the diameter or more.

Wet Flow Adapters

It provides another reference of flow visualization that is valuable in evaluating what is happening in the combustion chamber and helps to sort out problems in that area. It’s best when at an air/liquid ratio that represents the normal air/fuel ratio an engine uses. This process has helped solve problems that would otherwise go unnoticed.


Ever present at any testing is a flow tester on the phone comparing numbers with another tester. It provides an instant indication of hype vs. truth because known numbers are compared to claims.

These are basic tools you need on hand for airflow testing, which will provide incredibly insightful and helpful information.

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Useful Calculations for Comparing Flow Numbers

The necessity of flow-number comparison is something that anyone involved in flow testing must endure. Even if the number comparison is done on the same components and flowbench, it is important to know how to compare the numbers so the time and effort is worthwhile. The comparison process is necessary to evaluate published numbers vs. your own developed flow numbers. In flow testing, you’ll learn that you must ask (or qualify) at what test pressure the flow numbers were recorded.

The SuperFlow instruction manuals provide a chart for comparing flow numbers from one test pressure vs. another test pressure. If your copy isn’t handy or has been misplaced, we outline the information you need to know below.

The chart in the SuperFlow instruction manual for flowbench operations is based on the square root of the pressure ratio method. If you have flow numbers at a known test pressure and want to compare those numbers at a different test pressure, it’s easy to do.

As an example, if you have flow numbers at 10”H20 test pressure and would like to know what the flow should be at 25”H20 test pressure, the formula is: TBD on how to present it. You would multiple the flow numbers taken at 10”H20 test pressure by 1.58 to see what the flow should be at 25”H20.

Predicting Horsepower based on Airflow Numbers

The performance coefficient SuperFlow develop dis based on very accurate empirical data, and even 30+ years after its introduction into the marketplace, it is still a good indicator of power capability of an engine based on its airflow. Today’s engines are more efficient because of airflow improvements that were generated by thousands of people searching for more power.

The prediction of horsepower based on airflow numbers can be applied if the test pressure is known. The results are a good estimate of the engine’s capacity to make power if everything in the system is optimized to take advantage of the airflow available. An accurate estimate of the power capacity of the engine is dependent upon having accurate flow numbers for the complete airflow system, including the cylinder head, manifold, carburetor or fuel injection system.

The power coefficient varies with the test pressure. The following can be used for a quick evaluation of airflow numbers at different test pressures.

The equation: HP/cyl=Cpower x Test Flow, where Cpower = Coefficient of power, Test Flow = cfm flow at the same test pressure that the Cpower is applied.

Cpower for:

  • 10”H20 = .43
  • 15”H20= .35
  • 25”H20= .27
  • 28”H20= .26

These numbers assume the engine is using gasoline for fuel.

Example: If you have system airflow numbers recorded at 25”H20 and the flow as 200 cfm, the calculation would be HP/cyl = .27 x 200 = 54HP/cyl. If you were working on an eight-cylinder engine, then 8 x 54 = 432HP capacity. This assumes that each port flows the same number. More accurate results can be applied if the same calculation is made for each port of the airflow is now the same.

Predicting Peak Power rpm based on Airflow Numbers

Predicting the rpm at which peak power will occur, based on airflow, is an additional useful way to evaluate airflow numbers and an easy way to see the effects of changing engine displacement.

The equation: RPM at peak power = [(Crpm) / (displacement / cyl)) x cfm]

Where Crpm = Coefficient for peak power rpm calculation, displacement / cyl = displacement per cylinder in cubic inches, cfm = cubic feet per minute from flowbench data taken at a given test pressure.

Crpm for:

  • 10”H20= 2,000
  • 15”H20= 1,633
  • 25”H20= 1,265
  • 28”H20= 1,196

These numbers assume the engine is using gasoline for fuel.

Example: Using the same numbers that were applied in the previous example for power/cylinder above (200 cfm at 25”H20 and the engine is an eight-cylinder engine with a displacement of 355 cubic inches), 355/8 = 44.375 cubic inches per cylinder. Applying the equating and solving for rpm at peak power, where RPMpp = (1265/44.375) x 200 = 5,701 RPM.

Just for fun, what would happen to this number if the engine was 455 cubic inches? Now the engine displacement divided by the number of cylinders yields an entirely different number. So, 455/8 = 56.875. Applying the equation for rpm at peak power, RPMpp = (1265/56.875) x 200 = 4,448 RPM.

Many applications involve a specific need to know the airflow of engine components and how the engine uses air. Applying simple equations can compare the airflow of components. Many relationships can be enhanced if the airflow is known including valve timing (camshaft selection), inertia tuning factors of intake, power per cylinder capacity and the rpm at which peak power will occur.

You can learn some very interesting things by studying airflow through engine components and the engine itself. Because the engine is a self-driven air pump, many of the characteristics of the engine are set by its capacity to flow air.

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History of the Flowbench

An air flowbench is essentially a device that measures the resistance of a test piece – a cylinder head, manifold, carburetor, throttle body, exhaust systems – to flow air. Many different designs and models are on the market today that allow for comparison of flow results before and after changes in the flow path occur. Here’s a look at the history of this device.

Flowbenches and airflow data have been a part of the internal combustion engine development cycle for design, research and development for many years.

  • 1900s – Some of the first engine airflow studies, using some type of flow testing, occurred.
  • 1960s – Starting to study engine airflow and flowbench information and the relationship to performance in the racing industry

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 the kitchen tables, shops and garages everywhere. More elaborate and complex benches had been around for some time when the first SuperFlow model was available, but never in such an easy-to-use configuration. As market demand and understanding grew, many larger models were made available as racers began to compare flow information. Thousands of benches are in use every day, and engine component airflow technology is growing rapidly.

The first airflow benches in use at the Original Equipment Manufacturer (OEM) level were expensive, cumbersome and complex machines. They 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
  • Chevrolet – did not have a flowbench lab in use until the 1970s
  • American Motors – used flowbench-guided cylinder head designs in the early 1970s
  • Chrysler – adapted a flow lab from elements that were used in air filter work, and the lab was developed in parallel with their introduction of the 426 Hemi engine
  • Ford Motor Company – flow labs date to the mid-1960s, where they supported their winning LeMans racing effort with their GT40 racing vehicles

Some of the OEM, specialty-engine manufacturers and professional race teams are now using Computational Fluid Dynamics (CFD) to assist in Computer-Aided Design (CAD) and flowbench-driven designs. Many of the OEM have abandoned their in-house airflow benches and outsource much of their airflow development testing. As a result, some well-established shops using SuperFlow or other flowbenches typically get involved in OEM development contracts because the programs are more time and cost-effective.

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