MSD 2922 Installation

Atomic EFI Return System

PN 2922

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Thank you for selecting the Atomic Fuel Line Return kit. This kit is recommended for use with the
Atomic Throttle Body EFI and Atomic LS EFI systems.

Parts Included:

1 - Adjustable Regulator
1 - -6AN Port Plug
3 - -6AN Straight Port Fittings
2 - -6AN 90° Push-Lock Fittings
2 - -6AN Straight Push-Lock Fittings
15 Feet - High Pressure Fuel Hose

CAPABILITIES

The Atomic Adjustable Regulator is configured for a single -6AN inlet, and dual -6AN outlets (for
regulator-to-tank line routing flexibility). The recommended operating range is 0-90 psig (pounds
per square inch gauge). The maximum recommended flow rate is 500 liters/hour (2.2 GPM). The
vacuum/boost compensation ratio is 1:1.

1 - Regulator Parts Bag includes:
1 - Regulator Mounting Bracket
1 - Brass Hose Barb Fitting
1 - Stainless Steel Pipe Plug
2 - 10-32 x 0.375 Button Head Cap Screws
1 - High Pressure Fuel Hose Clamp

RECOMMENDED PLUMBING SCHEMATICS

Use the schematic below as a guide when installing the kit in conjunction with an Atomic throttle body
EFI system. There are two possible connection points on the throttle body unit, one of which will be
the fuel supply in an operational system. DO NOT “tee” into the supply line and leave the -6AN port
plug installed in the remaining throttle body port. Remove the -6AN port plug from the throttle body
and route fuel from that port to the regulator inlet port (using the supplied hose and fittings). The
hose length between the throttle body and regulator is not critical, but generally speaking, should be
kept to a minimum. Route and secure the hose as necessary to prevent chafing, stretching due to
engine movement, and heat-related damage.

CORRECT FOR RETURN STYLE FUEL SYSTEM.

FUEL

FILTER

MSD ADJUSTABLE

REGULATOR

FUEL

PUMP

FUEL TANK

Figure 1 Atomic TBI Return Fuel System.

MSD •  WWW.ATOMICEFI.COM  •  (915)  857-5200  •  FAX  (915)  857-3344

2 INSTALLATION INSTRUCTIONS

, MOUNT

ACCOMMODATES

Use the schematic below as a guide when installing the kit in conjunction with an Atomic LS EFI system.
There are two possible connection points (one at the rear of each fuel rail assembly). One rail will be
connected to the fuel supply in an operational system. DO NOT “tee” into the supply line and leave
the opposing fuel rail plugged or capped. Fuel from the opposing rail should be routed to the regulator
inlet port (using the supplied hose and fittings). The hose length between the rail and regulator is not
critical, but generally speaking, should be kept to a minimum. Route and secure the hose as necessary
to prevent chafing, stretching due to engine movement, and heat-related damage.

FUEL RAIL

(UNDER COVER)

FUEL RAIL

FUEL RAIL

(UNDER COVER)

(UNDER COVER)

MSD ADJUSTABLE

REGULATOR

FUEL

FILTER

FUEL TANK

FUEL

PUMP

IT IS RECOMMENDED TO MOUNT
THE FUEL PUMP IN THE TANK
WHENEVER POSSIBLE. IF IT MUST
BE MOUNTED EXTERNALLY
THE PUMP WITHIN 2-FEET OF THE
FUEL TANK SENDING UNIT.

Figure 2 Atomic LS Return Fuel System.

The regulator-to-tank connection should be made using the supplied hose and fittings. Install the
supplied -6AN port plug in whichever regulator return port is not used. Depending on the configuration
of your fuel tank / fuel cell, the supplied high pressure fuel hose clamp may be used at the tank fitting
connection.

Use care when routing the hose from the regulator to the tank. Route and secure the hose as necessary
to prevent chafing, stretching due to engine movement, and heat-related damage.

REGULATOR MOUNTING

Using the two (2) supplied 10-32
x 0.375 Button Head Cap Screws
and a 1/8-inch hex key (Allen
wrench), attach the regulator
bracket to the regulator body. The
regulator may then be mounted
to the firewall, or other convenient
surface. Regulator orientation
is not critical, but be mindful of
adjustment screw access and hose
routing. Refer to Figure 3 for a
mounting bracket template.

2.200”

#10 SCREW

Figure 3 Regulator Mounting Bracket Template

MSD •  WWW.MSDPERFORMANCE.COM  •  (915)  857-5200  •  FAX  (915)  857-3344

INSTALLATION INSTRUCTIONS 3

VACUUM / BOOST

ADJUSTMENT SCREW

INLET PORT

GAUGE PORT

REGULATOR CONNECTIONS AND ADJUSTMENT

The regulator inlet port is located on the bottom surface, and clearly marked with an identifier machined
in the housing (see Figure 4 below). Two (2) outlet ports are available, but typically only one (1) will
be used. Install the supplied -6AN port plug in the unused outlet port using a 5/16-inch hex key (Allen
wrench). The -6AN straight port fittings should be snugged with an 11/16-inch wrench or deep socket.

Install the supplied 1/8-27 NPT brass hose barb fitting in the upper regulator housing (see Figure 4
below) using a 7/16-inch wrench or deep socket. Thread sealer is not required on this fitting, but
can be used if desired. Connect an intake manifold vacuum / boost source to this fitting, or leave
it open to the atmosphere if manifold pressure compensation is not required. DO NOT plug this
opening. Ensure that contaminants (such as water and road spray) cannot enter the open fitting.
In the event that vacuum / boost reference is not required, a more cosmetically pleasing option is to
install a sintered metal exhaust muffler in this port (such as McMaster-Carr PN 4450K1-Bronze or PN
4402K51-Stainless Steel)

The 1/8-27 NPT port in the lower housing allows the installation of a fuel pressure gauge (direct or
remote-reading). If use of this port is not required, install the supplied stainless steel pipe plug using
a 3/16-inch hex key (Allen wrench). Use of a fuel compatible paste-type thread sealer is REQUIRED
on this plug. Thread sealing tape is also an option, but not recommended due to the potential for
particulate and debris generation.

Use a 5/32-inch hex key (Allen wrench) to adjust the regulator set point. Clockwise rotation (screw
advancing inward) increases the set point, and counter-clockwise rotation (screw advancing outward)
decreases the set point. When the desired set point has been reached, snug the jam nut using a
½-inch wrench.

Refer to the user installation instructions, supplied with the Atomic EFI kit, for regulator set point
recommendations.

Note: An overly lengthy and restrictive return line routing scheme may result in a non-negligible

pressure rise across the regulator-to-tank portion of the system. For this reason, the final
regulator adjustment should be made while monitoring the system fuel pressure (on the Atomic
hand-held Dash) with the engine at idle.

AND LOCK NUT

REFERENCE PORT

(1/8-27 NPT)

(1/8-27 NPT)

MOUNTING

BRACKET

OUTLET PORT

(1 OF 2)

MSD •  WWW.ATOMICEFI.COM  •  (915)  857-5200  •  FAX  (915)  857-3344

Figure 4 - Regulator Feature Identification Guide