This is a return-style regulator. The fuel enters from the right througha -8 AN line and exits on the left. If you set the regulator for 8pounds, additional fuel would constantly be flowing through the lowerport and back to the fuel tank.
If you are stubborn and want a dead-head-style system or are clicking off 1.20 60-foot times in a trailered race car, BG offers the BG400 pump, which has an externally adjustable bypass right at the pump that can return fuel to a rear-mounted fuel cell or tank. It's really not designed for street use, but for burger-stand guys and short trips, there is a power stepdown box that will cut the voltage to the pump so it will not overheat. A toggle switch is used to put it into street driving mode, then a throttle switch takes the system back to full voltage at WOT. Pretty neat.
If you still insist on trying a dead-head system, there is the Enduro series from BG, which allows you to run a big electric pump on the street. The trick is an internal bypass and a fuel-cooled gerotor-style motor. The King, Mighty, and Speed Enduro pumps can feed 2,000-, 750-, and 500hp engines respectively and can also be hooked to an additional aluminum heat sink if necessary for additional abuse.
There are a couple of ways to get fuel from the tank and into the fuelpump. This is an aluminum fuel cell from Summit Racing. It has two -8feed lines built into a rear sump and is designed to be mounted in thetrunk by either cutting a hole or raising the cell above the trunkfloor. We've heard that you must supply the pump with -10 AN or betterso that if you had to, you could run a Y-block from both -8 ports to a-10 or -12 line. | 
If you select a plastic fuel cell, you can drill out the -8 hole and adda larger fitting and line. We don't know why fuel cells are equippedwith -8 when fuel-pump guys require -10 or -12. Ask that question nexttime you are on the Summit Racing tech line. |
This of course is the trickest way to deliver fuel and also the mostexpensive. If you have a car that no one makes sumps for, you can takeyour tank to a willing radiator shop and get them to weld in a sump kitlike this one from Competition Engineering, or have a complete tankbuilt by a company like Rick's Hot Rod Shop in El Paso, Texas. They willdo whatever you want... for a price. | |
RegulatorsAt the very low end of the fuel pump spectrum you can find fuel pumps that don't require a pressure regulator of any kind. They are the mechanical pumps that provide less than 110 gph free flow and don't build pressure much higher than about 8 psi, and electric pumps that provide less than 100 gph free flow and don't build pressure above 7 psi. If you need more pump, you need a regulator.
Using Holley carburetors as an example, the needle-and-seat assembly can control fuel flow up to about 8 psi. Any more than that and unregulated fuel will flood the bowl, enter the carb through the venturi as it pours out of the vent tubes, and stall the car at idle or create a huge rich condition at full throttle. The regulator simply uses spring pressure to regulate fuel pressure. There is a screw or Allen bolt on top of the regulator that when turned clockwise adds preload to the spring, increasing the amount of pressure required to unseat the regulator. A dead-head-style regulator simply stops fuel from flowing when the valve is closed. A return-style regulator allows fuel to flow back into the tank. There are several sizes available, but the basic breakdown is for either 31/48-inch or 11/42-inch fuel line. There are also four-port regulator dead heads for tunnel-rams and single-return styles for multiple carbureted street machines.
When using return-style regulators, it's important that the return line is within one size of the feed line. If the line is too small, fuel will not be able to return to the tank fast enough and you will not be able to lower the fuel pressure at the feed line no matter how many times you turn the screw.
This is a cutaway of the BG400 vane-style pump. As you can see, it issimilar to a starter motor, with a shaft that turns a rotor submerged inthe fuel supply. On the right is a bypass that is designed to returnfuel directly to the fuel cell. | 
When returning the fuel to the tank, try to do it as far away from thepickup as possible. Never return fuel to the extra AN fitting next tothe feed port on the sump, because it will disrupt flow. Most fuel cellswill have the return port in the correct place and the proper-sized,NHRA-legal vent. It's important to note that when you place a fuel cellin the trunk, you need to have a firewall between the trunk and thepassenger compartment. |
This is a photo of the horrors of cavitation. When the pump cannot pullenough fuel fast enough, air pockets develop and stir bubbles into thefuel and, in some cases, damage the pump. A good pickup and feed line,plus mounting the pump as close to the tank as possible, will preventthis problem. | |
Since every pressure regulator has fuel pressure versus spring pressure vented to atmosphere, you can run a fitting to manifold pressure. On boost, the extra atmosphere will increase fuel pressure at a 1:1 ratio. Nitrous guys should have a separate fuel system for safety reasons. If the main fuel system fails at full throttle, the nitrous will still be spraying. With a separate line you can run a safety switch that kills the nitrous when fuel pressure drops below a predetermined limit.
Fuel LinesWe've been having a small debate about the size of the feed line from the fuel tank or cell. BG recommends a -12 (31/44-inch) line for the BG-400 and even sent us a photo of a cavitated pump as proof that bigger is better. The theory is that since electric pumps are designed to push and not pull, they need all the help they can get. Yet most fuel cells come with a -8 (11/42-inch) line, and the guys at Holley saw no problem with a -8 feed. What BG and Holley agree on is that the primary line should be -8 (11/42 inch) from the pump to the regulator and at least -6 (31/48 inch) on the way back.