Why is Fuel Filter Better?

Water in fuel causes rust and other chemical corrosion that can alter injection system surfaces. In high-pressure common rail (HPCR) engines, even the slightest change to a surface can impact performance due to the extremely tight and precise tolerances used by the system to perform its jobs effectively.

Primary fuel filters, also known as fuel filter water separators, use a variety of methods to separate water from fuel. Accumulated water can then be drained from the filter drain valve during recommended service intervals. The primary fuel filter offers low restriction because it’s mounted on the suction side of the fuel pump. This filter also protects the transfer pump from contamination and wear, and typically works in tandem with a secondary fuel filter.

tl dr: I don't see how they can make that specific claim.

I'm not sure how they can claim it increases fuel flow. What it can do is allow more fuel to flow by reducing a restriction in the fuel system. I realize there may be a fine line here between the two lines of thought. The claim it "increases" to me means it does something which actively puts more fuel through the lines. The thought of "allows more fuel to flow" is of the idea that by removing the restrictive stock filter, you allow the fuel to flow as it has the ability to flow. It may end up being the same in the end, but to me there is a difference. To me the difference is like saying (for instance), putting an electric water pump on a car creates horsepower. It doesn't do that, it just frees up horsepower which was already there, but was getting utilized to run the belt driven pump.

As for the fuel pressure regulator, remember what the FPR does ... it controls the pressure and not the flow. It does create a large obstruction in the fuel line which creates the pressure, but that's it's job. It cannot speed up or slow down the flow of the fuel going from the pump into the engine in and of itself.

There are two main parts which control the flow of the fuel. First is the fuel pump. It provides the main output which equates to the rate of flow. Secondly is the size of the lines taking it from the pump to the engine (and return line as well). If you want the ability to flow more fuel, you have to have a large enough pipe to handle it. You can effectively increase the flow by increasing the pressure. (NOTE: This may seem to contradict what I was saying earlier about the FPR, but again, the FPR doesn't in and of itself increase the rate of flow, but rather controls the amount of pressure. These are two separate things.) At the fuel injector, the more pressure equates to more fuel being dropped during a given injector cycle time. At a given pressure, you can increase the flow by increasing the size of the line carrying the fuel as long as the pump can deliver it.