All of Griffin’s filters are sized or rated by Flow Rate. Whether measured in Liters per Hour or Gallons per Hour, the flow rate of a filter describes the amount of fuel that the filter can process with a clean element and no restrictions to the incoming or outgoing fuel flow pathways. Using a filter that is rated below your required flow rate might starve your engine of fuel and cause all sorts of problems. Using a filter that is rated too high above your required flow rate will cost you more in the initial filter purchase price as well as the higher prices of the larger replacement elements. The best way to determine the flow rate needed for a particular installation is to consult the documentation provided by the engine manufacturer or speak with a technical support representative with the company whose product you are using.
That being said, sometimes it is not possible to get that information and we must go by rule of thumb. When I started in this business, one of the first things I wanted to learn was how to properly size a diesel fuel filter. I came across this website, http://www.bluecollarman.org/Boattalk.html, that said in order to estimate required flow rate, multiply the engine’s horsepower by 18%. The resulting number is the flow rate required in GPH (gallons per hour). The rule of thumb that I use today is to take the horsepower of the engine and multiply by 20%. I know that the referenced website says to use 18%, but let’s face it, multiplying anything by 20% is just a heck of a lot easier to do on the fly than 18%. It also provides a good starting point for you to then factor in any other aspect of the installation which would necessitate either an increase or decrease in your required flow rate. This rule of thumb works for standard diesel fuel applications and would need to be adjusted accordingly when used to size filters for WVO or non-standard diesel fuels due to the difference in fuel viscosity.
General Flow Rate Rule of Thumb: HP x 0.20 = Estimated Flow Rate Required