The maximum ACTUAL CFM of the standard 2 inch Flow Quik is 330. Heads that flow more than this at 28 inches, can still be tested at less than 28 inches and Flow Quik will provide flow values adjusted to 28 inches. Minimum measurable flow is 7 CFM. 23 degree Small Block Chevy Below 330 cfm

The maximum ACTUAL CFM of the 3 inch Flow Quik is greater than 700 CFM. Minimum measurable flow is 17 CFM. If your air mover is too weak to supply what your head flows, you will be better off using the 2 inch model. The 3 inch Flow Quik does not include the flex hose that comes with the 2 inch model.

Flow Quik works with a vacuum source that you supply. This can be your shop vacuum or a more powerful source. (See Flow Quik Tips & Advice for hints on vacuum sources.) It does not control the amount of vacuum (commonly called "depression"). Instead, it measures the depression and the flow, and then adjusts the displayed flow to what it would be at the standard depression. You select the standard depression by the range **** on the front panel. The method Flow Quik uses to calculate this adjustment is a well established principle of fluid dynamics, and is recommended by the largest flow bench manufacturer (Big Blue, and we don't mean IBM).

Flow Quik uses an averaging velocity tube to measure flow. The velocity tube and the orifice (commonly used in flow benches) are both members of a broader classification of flow measuring devices called differential producers. With both of these, the flowing air produces a pressure drop that is proportional to the square of the flow. The combination of this nonlinear response and high pressure drops gives the orifice a limited range. This is why flow benches need several orifices of different sizes.

Flow Quik's averaging velocity tube can measure a broader range than an orifice because it's a low constriction design has a low pressure drop. It's range can be further extended because it does require that depression be controlled. Heads that flow beyond its normal capacity can be tested at a lower depression. Flow Quik senses the lower depression and corrects the flow figure to what it would be if the depression were at the standard value.

When testing the Audie Flow Quik, we used this $39, 2.5hp Sears shop vac and flow tested successfully to about 230 cfm. A 4 or 5 hp unit would certainly deal with the requirements of a 300-cfm head and this would cover most needs.