Regulator Selection Guide:
2-Port (Carbs) w/o return - For one carb with a dual inlet or two carbs with single inlets.
4-Port (Carbs) w/o return - For engines with two dual inlet carbs.
3-Port (Carbs) w/return - Same as 2-port above but in vehicle using EFI fuel pump w/return line.1
5-Port (Carbs) w/return - Same as 4-port above but in vehicle using EFI fuel pump w/return line.1

2-Port (EFI) - Use this in EFI systems where only one outlet to fuel rails is required. Has return port.
4-Port (EFI) - Use in EFI systems where up to three outlets to fuel rails are required. Has return port.
Ford Mustang Regulators are replacement for stock regulators but provide adjustability.

1. If the vehicle was originally equipped with a high pressure EFI pump and return line and you are now switching to a carburetor, you need a regulator to drop the pressure to the 4.5 to 9 PSI range
for carburetors. That also allows you to hook up the stock return line. Without a return line, the original EFI fuel pump will supply too much pressure and volume to the regulator. Note that many 1999
and later vehicles utilize a "returnless" system. Both the fuel pump and regulator are in the gas tank. If you are installing a carburetor on one of these vehicles, you will need to remove the regulator and
pump, or disable them, and use an external fuel pump suitable for carburetors and one of our conventional carburetor style regulators such as the 10650/10651/10656/10657/10660/10661.

Find out more...

The Fuel Pressure Regulator Lineup

An explanation about "ports."

If you have studied the various descriptions of regulators you will
find that the definition of "ports" can be very confusing. Especially when it comes to regulators with a bypass
(return) line. In all of our designations,when we say "2-port" or "4-port" that means the total number of outlet ports, including a return or bypass line port if the regulator is so equipped. For example, our 5-port models have one inlet port and five outlet ports, one of which is a return or bypass line port. So there are still four usable outlet ports.