The ability of an engine to take in air and use it as fuel is the most crucial factor in determining how much power it can produce, regardless of the size of the engine. We are looking for the least possible restriction to the airflow at every stage, beginning with the air filter and working through the throttle, the head(s), and finally, the exhaust. Therefore, it should not be surprising that an apparatus that measures airflow, known as a flow bench, is of the utmost importance.
A flow bench is essentially an elevated version of a vacuum cleaner in which air is sucked through an opening with a huge diameter. On most test benches, the flow direction can be changed so that air is either blown or sucked through the test object; these settings are referred to as the exhaust mode and the intake mode, respectively.
The machine automatically adjusts airflow volume so that a constant level of flow restriction is maintained through the object being tested. This limitation is referred to as the test pressure, expressed as a measurement in inches of water.
The flow bench needs to be calibrated before any testing can begin. This is done to determine the maximum airflow volume at each of the six different motor settings. This flow volume is measured in cubic feet per minute (ocfm), which is cubic feet per hour—the flow scale. After the complete calibration process, the airflow volume that passes through the tested object will be displayed on a manometer scale as a percentage of the flow scale peak figure. As an illustration, a cylinder head that can flow 50 percent of the volume measured in cfm on a flow scale of 200 cfm is capable of 100 cfm.
Westech Performance Group is the owner of this Superflow SF-600 flow bench, which can be seen in the picture (note that Superflow is one of the most recognized flow bench manufacturers in the world).
You should first get an adapter that enables the flow bench orifice to make an airtight attachment to the test object. This should be done before anything else. Suppose you want to test something a little out of the ordinary. In that case, you will need to fabricate your cylinder head adapters because most experienced flow bench operators have a variety of cylinder head adapters that are already assembled and ready to use.
For instance, to test an intercooler with fittings measuring 3 inches on a Superflow SF600, you will need to drill a hole measuring 3 inches through a flat sheet of metal and then weld a section of pipe measuring 3 inches around the circumference. After that, you will need to drill through the flat sheet with a drill that has a bit with a diameter of 1/4 inch and a spacing of 5 inches square; this will allow the adapter to be securely bolted to the flow bench.
After the test object has been mounted on the bench, the operator will choose the appropriate flow direction and a flow range before running the test. The operator should know approximately how many cubic feet per minute (cfm) a specific test object should flow at given test pressure. The operator can guess the appropriate flow range required for a particular test.
Although a test pressure of 28 inches of water is used for most applications, this value can be adjusted as needed. The test pressure of ten inches of water, for instance, can be used to measure the diameter of the cylinder head of a motorcycle. Be aware, however, that the electric motor’s attempt to maintain a low air volume can cause it to overheat.
To obtain precise readings of the bench’s cfm, it is frequently necessary to radius any sharp edges through which the court may be drawing air. Although it may appear that radiusing the edge would falsely improve airflow, we have been assured that all it does is remove any “misrepresentation.” It is common practice to place a bead of plasticine around the edge of cylinder head ports to ensure no turbulence at the mouth of the harbor.
A flow bench can be used to test nearly every component of an engine that moves air through it.
The most common use for a flow bench is to measure the performance improvements brought on by porting the cylinder heads of an engine. Typically, a “before” and “after” test will show where the most significant advances have been made. It is essential to keep in mind that the flow bench is ideally suited for analyzing cylinder heads because it can be configured to draw air in through the inlet port and switched to draw air out through the exhaust port, thereby recreating the flow directions that occur within the engine.
In addition, the flow that passes through the cylinder ports can be measured at various valve lifts in the system. There is no point in only testing flow when the valves are fully open. Instead, you need to measure flow through various lift increments to get an accurate reading. Because the valve spends most of its time at this lift set while the engine is operating, the flow through the port when the valve is in the middle of its travel is critical. The flow bench operator should have a collection of valve spring tools suitable for your head and can be used to adjust the valve opening on the flow bench using a custom-made tool for the valve spring.
It is possible to calculate the maximum potential power when testing heads with a flow bench, which is yet another advantage of using one of these benches. Apply the following formula:
Calculating Potential Horsepower: 0.256 times the volume of air moved at 28 inches of water times the number of cylinders.
In addition to cylinder heads, a flow bench can be used to examine airflow through catalytic converters, blow-off valves, inlet manifolds, intercoolers, air boxes, and mufflers, among other components. If there is sufficient open space in the test room, you can flow an entire exhaust system from end to end. However, it is essential to note that whatever you test must be clean. If it is not, the stray matter could potentially damage the machine.
Regardless of whether the engine has 2, 3, 4, or 5 valves per cylinder, the standard cost to flow test a head is 55 Australian Dollars (AUD) per cylinder. Other kinds of testing have prices determined on a case-by-case basis, and it is essential to keep in mind that you might have to make your adapter. Regardless of the specific cost, utilizing a flow bench is an excellent method for contrasting and analyzing a variety of go-faster equipment.