A decent rule of thumb is a factory-style fuel delivery system will support up to around 500 hp. After that, a 550 to 600-plus horsepower engine will require a fuel delivery system capable of flowing a significant volume of fuel to ensure the carburetor or injectors have adequate fuel to use. Many manufacturers offer flow graphs in their catalog that rate fuel flow at various pressures. These graphs are very helpful in determining fuel flow. If you're still unsure as to what you need, contact your favorite manufacturer's tech line and get its recommendation. Most companies also offer complete fuel delivery system kits like Aeromotive's Fox-body Mustang kit that includes a fuel tank, lines, pump, regulators, and all the lines and fittings designed for that car. The kit is very complete, but also expensive.
Pressure Vs. VolumeIt doesn't require an engineering degree to see that it takes pressure to move gasoline from the tank to the engine. Add the g-force load of a fast car on the dragstrip and that same acceleration that pushes you back in the driver's seat also makes the fuel pump's job of pushing fuel forward doubly difficult. Buried in some obscure engineering handbook somewhere is the concept that as pressure increases in a fuel system, the volume delivered decreases, or, volume is inversely proportional to pressure. This is clearly evident when you look at a flowchart for any pump. As pump pressure increases, this reduces the amount of fuel the pump can deliver because it is squeezed through a smaller orifice.
So it makes sense that you would want to design your fuel delivery system-the lines, fittings, filters, and pressure regulator-to be carefully matched to the style of pump you will be using. One of the most common misconceptions about fuel delivery systems is that a too large fuel line (such as -10 or 51/48-inch id) creates a huge pressure drop in a drag car because g-forces work against a large surface area. This is not true. While the volume and therefore the weight of fuel in a larger-id fuel line is greater, the real variable in this situation is the length of the fuel line from the front of the car to the rear.
Try this-imagine a column of fuel in a vertical tube 31/48-inch id and 15 feet tall. If we increase the diameter of that tube to 11/42 inch, does the pressure (in psi) measured at the bottom of the larger tube change? The answer is no. While the weight of that column of fuel increases with the larger diameter, the pressure per square inch does not. Think of the standing height of a column of water behind a dam. It doesn't matter whether you slide a long 11/42-inch tube or an equal-length 1-inch tube to the bottom of the dam and measure the pressure at the bottom-both tubes will measure the same. Now, if we shorten the height of the vertical column, the pressure at the bottom of that column will be reduced. Conversely, increase the height of that column and the pressure at the bottom will increase.
Now let's lay that vertical column horizontally and place it in a drag car. A vertical tube works against the force of gravity-or 1 g. Now, let's say our car launches very hard and can generate an initial acceleration rate of 2 g's. Increasing the distance from the fuel tank to the regulator will create a greater pressure drop in the system. That's why Top Fuel cars place the fuel tank ahead of the engine-to make it easier for the pump to maintain fuel delivery pressure under a sustained 4 g's. This is why high-g launch cars (and cars that commonly reach for the sky) need higher fuel-system pressure to overcome the initial pressure drop as the car accelerates. Isn't physics cool?