How to identify if your LS engine is a return or return less fuel system. 

We often get asked what type of AN fuel line kit is needed for an LS swap and that starts with identifying if the engine uses return style fuel rails or returnless style fuel rails. 

On an LS based engine the fuel pressure must be regulated and this is managed with a fuel pressure regulator, where this regulator is placed in the system determines the type of system you have.

Return style fuel system LS engine

In what has been termed a return style fuel system the fuel pressure regulator is integrated into the fuel rail on the LS engine itself. In this type of system you will have a fuel line running up to the fuel rail and return line also coming back from the fuel rail. In a return style fuel system you will require an in-line fuel filter 10 micron or better to complete the system. This type of system can be identified as the fuel rail will have fuel ports for both the fuel feed line and fuel return lines. 

Return-Less style fuel system LS engine

The Return less style fuel system has misconceptions about what return-less actually means. In this style of fuel system the fuel pressure is externally regulated. The fuel pressure regulation can be accomplished a few different ways, usually when doing an LS engine swap this is accomplished by utilizing an external fuel pressure regulator.

Corvette style filter and regulator unit

Our Return-Less LS engine swap kits include a "Corvette style filter regulator"  that regulates the LS engine to the needed 58 PSI this unit also doubles as the fuel filter and is a very cost effective way to regulate the pressure. The limitation with this regulator is in high flow fuel systems it may not be enough, this leads us into aftermarket adjustable fuel pressure regulators. 

Aftermarket fuel pressure regulators

Aftermarket regulators will allow the required fuel pressure to be set but also support high flow fuel pumps. You will need an inline fuel filter with these aftermarket fuel pressure regulators. Aftermarket regulators can also be adjusted to support advanced tuning and often times are boost referenced so that they increase fuel pressure as boost increases again to aid in tuning of the LS engine. 

Other fuel pressure regulation methods

Internally regulated modules OEM and Aftermarket

The two less common methods of regulating fuel pressure for LS engine swaps are the us of internally regulated fuel pump modules, these exist in certain OEM systems as well as some retrofit fuel pump units by various aftermarket manufacturers. The advantage of some of these systems is simplification of the install as only one fuel line to the engine is required making them truly "return-less" these systems are usually system specific so we recommend you reach out to us for assistance in selecting the correct unit for your application. The disadvantage of this type of system is serviceability, if you have issues with the internal regulator you will be dropping the fuel tank. 

PWM or Pulse Width Modulation

While very common in newer OEM applications PWM is less common in the aftermarket. With this method the fuel pressure is controlled by the Engine ECU. While possible to implement it does take more work to accomplish an engine swap. The ECU controls the pump by applying signals to control the output of the pumps volume and pressure thereby delivering the fuel needs to the engine. 

Always happy to help

If you have more questions about what fuel system is best for your application please Contact US and we will be happy help.