Dynamic Range Explained
The dynamic range of an injection system is an often mis-understood item. Dynamic range denotes the system’s ability to meter flow from the “lowest to the highest” or the max spray divided by the minimum accurate spray of a system. For example, a system that can control a spray between 100 to 500cc/min has a dynamic range of 5.
We will use a fuel injector as a reference. Take a 500cc fuel injector, and using a simplistic look at the range, dismissing many variables, if the injector can operate properly down to 1%DC, or 5cc, then it would have a 100:1 dynamic range (500cc / 5cc = 100). In real conditions, a wide dynamic range is needed to operate an engine correctly.
Most water/alcohol injection systems on the market use a progressive pump speed system( or PPS system) to deliver fluid. What this means is there are no modulating valves to control the flow, just the varying speed of a pump. This type of system follows simple physics that dictate a fluid system requires 4 times the pressure change to create twice the flow. So an injection system will have to go from 60psi to 240psi has a dynamic range of 2.
The Pulse Width Modulated valve system uses a high speed inline valve to control flow. The pump simply maintains a constant pressure. These valves, while operating similarly to a fuel injector, typically can deliver a 10:1 dynamic range. This means for a 500hp engine, the PWM valve system can deliver linear flow from 50hp on.
If you look at various dyno charts, you will notice a minimum dynamic range of 5:1 is necessary. For a daily driver, dynamic range of 10:1 is preferred, this covers partial throttle to WOT and many load conditions. A system with a a wide dynamic range system is generally be better suited to all applications.