How to fuel a GM Direct Injected LT1, LT4, and LT5 crate and modified engines
Let’s Talk GM LT-Series Direct Injected Crate Engines
The latest arsenal of GM crate engines includes the new LT series engines.
The two most popular are the naturally aspirated LT1 and the supercharged LT4.
The LT5 is out of production but lives in many long-term project vehicles.
High and Low Pressure Fuel Systems
The part that throws some folks off is that GM refers to the High Pressure Fuel and the Low Pressure Fuel systems. The intank or inline pump is often referred to as the lift pump, and the engine mounted pump is often referred to as the mechanical pump.
The first thing to remember about direct injection (DI) engines is that they are no more difficult to feed fuel to than an LSx/Gen4 or any other port injected engine. In fact, it is easier to feed a DI engine than a port injected engine. For DI the engine mounted mechanical pump increases pressure from the lift pump (in-tank or inline pump) from low (say 60psi as an example) to 2000+ psi at the injector. As long as the mechanical pump cavity is filled, even if the lift pump pressure is not exactly on target, the system will work fine. On the other hand, nearly all port injected engines need to have the fuel pressure tightly controlled so the injector can dispense the correct amount of fuel.
In linear fashion…
Low pressure fuel system ==> High pressure system / mechanical pump ==> Direct Injectors
The high pressure pump is 2000+ psi, far higher than automotive electric fuel pumps can supply. However, the high pressure mechanical pump needs to fill with fuel from the tank, quickly, in order to pump fuel to the DI’s. That’s the job of the low pressure fuel system.
In the OEM application, the low pressure fuel system is almost identical to the systems used in the LS based cars. From a practical standpoint, they are the same.
In linear fashion…
Engine/Transmission PCM ==> Fuel System Control Module ==> In-Tank Fuel Module ==> High pressure mechanical pump ==> Direct Injectors.
Typically there are going to be two electronic control types for the LT engines: GM, and all the others.
The GM engine controller has a built-in FSCM. It will control a single fuel module just like the OEM application. It will handle one OEM type fuel module or pump well, but it does not have sufficient power capability support multiple fuel modules or pumps.
Previous GM FSCM’s also could not handle any significant additional power (two fuel modules, upgraded pumps, voltage boosters, etc.)
Nearly all aftermarket engine controllers (Holley, Edelbrock, etc.) do not have a built in FSCM. For these applications, a VaporWorx PWM system has shown to work well in single and dual fuel module applications with or without voltage boosters.
GM requires 70-72psi to feed the high pressure mechanical pump on LT1, LT4, and LT5. However, this high pressure is only needed under high fuel/high engine speeds. The need for the higher pressure is so that the mechanical pump cavity can completely fill during high demand/engine speeds where the open time of the mechanical pump is short. During idle and cruise, where the opening time of the mechanical pump is longer, a lower pressure can be used. Typically, using the VaporWorx controller in manifold referenced mode with an at-idle fuel pressure of 55-60psi works well.
For flowrates, be wary of the instructions provided by GM. As of Oct. 20, 2018 their online instructions had the same flowrates listed for the LT1 and LT4, with the LT4 being incorrect.
UPDATE: GM has again supplied the same pressure and flowrates for LT1, LT4, and LT5 engines.
UPDATE April 2023: GM has updated the fuel requirements for LT1 and LT4. Their recommendation for both is the Gen5 Camaro ZL1 fuel pump module, GM Genuine MU2101/100291, the same that VaporWorx has been suggesting since both engines were offered in crate engine form. The only difference in the recommendations is the LT1 is 45gph. The VaporWorx recommendations for these engines, in place for many years and shown in the next section, line up with the GM numbers. In GM’s own words:
START
This control system is intended for use with a returnless fuel system and fuel pump that is capable of being pulse width modulated (PWM) at 25 kHz to control fuel pressure. A fuel flow rate of 65.6 G/H at 58 psi (400) kPa is needed. Because this is a dead headed system, a pressure relief set at 84 psi (580 KPa) must be included in the fuel line between the tank pump and the engine mounted high pressure pump. Chevrolet Performance Part Number 19303293 is one example of a compatible fuel pump and it includes an internal pressure relief
system. If using this pump, the lower port on the module may be left open or used to connect a remote pick up system. P/N 13587174 is connector pigtail for this pump and is available from your local dealer (NOTE: VaporWorx has a color-coded pigtail or raw components as well).
A pump with excessive capacity may result in cavitation at low flow due to the pump repeatedly stopping and starting instead of controlling to a speed/pressure. Alternatively, a fuel system operating at a fixed 500 KPa could be used and a fuel pump relay may
be triggered by the Green/Gray wire in cavity 2 of the Fuel Pump Power Module (FPPM) connector. The Green/Gray wire is 12 volt positive side control for a fuel pump relay. Do not use or install the Fuel Pump Power Module if using this alternate method.
Diagnostic codes will be set in the ECM if the FPPM is not used, but will not illuminate the MIL (malfunction indicator light). Note that excessive fuel heating and potential startability/drivability issues may result from a constant high pressure.
END
Note that GM states that fuel overheating may cause a variety of problems, hence the recommendation to use a returnless PWM controlled fuel pump module.
For the LT5, supplied only in the C7 ZR1, either the OEM fuel module @ 14" tall or the Aeromotive 68101 will work well. For most project vehicles, the 68101 is short enough to fit most hot-rod chassis.
In short, it is suggested for excellent results to use the following:
LT1up to 700hp naturally aspirated: GM Genuine MU2101(with fuel level sensor) or M100291 (no FLS) or Aeromotive 68101. The 68101 will allow for horsepower growth.
LT4 up to 650hp: GM Genuine MU2101 or M100291 has shown to work well with zero engine modifications. The Aeromotive 68101 Super ZL1 will proved the same pumping performance as the OEM vehicle (Camaro ZL1) and is recommended for modified builds.
LT4 up to 750hp: Aeromotive/VaporWorx 68101
LT5 stock: Aeromotive/VaproWorx 68101
LT5 modified up to 900hp: Aeromotive/VaporWorx 67707
Let’s do some match and check the GM instructions........
A naturally aspirated engine needs approximately 1/2lb of fuel to make one horsepower for an hour. The 1/2lb per hour per horsepower is called the Brake Specific Fuel Consumption (BSFC). We’ll leave the units conversion out of the following:
460hp * 1/2 = 230#/hr
Gasoline weighs 6#/gal. So … 230#/hr / 6#/gal = 38.3gal/hr
The GM fueling specification for the LT1 is 45gph. Okay!! That makes for a nice 17% safety factor. The GM Genuine MU2101 or M100291 are excellent choices.
The LT4 on the other hand makes 650hp, but the BSFC on supercharged engines is typically higher at 0.6
More math!
LT4 ==> 650hp rating.
650hp * 0.6 = 390lb/hr
390#/hr / 6#/gal = 65gal/hr fuel requirement
The GM fueling specification for the LT4 is the same as the LT1 at 45gph.
Nope!
Hence, for the LT4, a pump with an output of 65gal/hr should be the minimum. The Aeromotive/VaporWorx 68101 is a good choice.
LT5 ==> 750hp rating.
750hp * 0.6 = 450lb/hr
450#/hr / 6#/gal = 75gal/hr fuel requirement
The GM fueling specification for the LT5 is the same as the LT1 at 45gph.
Nope Nope!
This is not the first time GM specified the incorrect fuel specifications for their crate engines. The LSA had two incorrect versions before finally coming out with the correct, but difficult to perform, fueling specifications.
So, which pump(s) to use?
For unmodified LT1 and LT4 engines, the Gen5 MU2101/M100291 and Gen6 Camaro ZL1 fuel modules will work well. The Gen6 Camaro and CTS-V3 are the same part. For most musclecar chassis the Gen5 is the best choice since it is significantly shorter.
For most all applications, the Gen5 ZL1 fits best and has fewer changes necessary to make work properly. GM Genuine MU2101 or M100291 (Gen5 Camaro) or GM GENUINE 84873933 (Gen6 Camaro) are good choices. These will work very well with the GM FSCM or Aeromotive/VaporWorx PWM kits. When any of these fuel pump modules are used the system will effectively be the same as a Gen6 V8 Camaro.
The Cadillac CTS-V2 (2009 – 2014) fuel module does not have the capability to feed 72psi to the high pressure side. It is limited to 65psi due to the safety pressure relief valve built in to the module.
Adding more power (750hp+) or E85 to the LT4 and LT5 will require a higher output fuel system. The suggested option is to use the dual pump Aeromotive KPM1500 fuel pump module . This has shown to be an excellent system for street, autocross, and road course duties for up to 900hp E85. Due to the power limitations of the OEM FSCM, secondary controller like the Ally DualX will seamlessly work with the GM system.
So the question becomes, what to do for e85 and higher horsepower?
If a true fuel module, like the GM ZL1 is desired, then two options may be considered:
Needed Small Parts for Installing the LT-Series of Engines
For each of the GM engine control systems, there are some parts that are needed for a complete installation when using the ZL1 module.
First, the kit does not come with the fuel module electrical plug. This plug is unique and does not fit anything else on the car except remote fuel level sensors.
The other is a way to adapt the fuel pressure sensor into the fuel line. Aeromotive has several options to make these swaps easier: Small parts
What About a Tank For My Restomod/Pro-Touring/Cruiser/Driver?
The GM fuel modules, along with nearly every other OEM, use a standardized tank-to-pump interface. The pump mounting height, electrical, plumbing attachments, etc. may differ.
Aeromotive offers stock-like tanks and modification kits that may be suitable for your build. Check for your model on the Aeromotive website or all our Tech Services line.
There are many companies that offer tanks that can support the GM ZL1 fuel pump module as well as other manufacturers products:
Rock Valley Antique Auto Parts: RVAAP can build custom tanks for any car, and are well known as the supplier to Roadster Shop and Detroit Speed: Rock Valley
Rick’s Tanks: Rick’s makes show-quality tanks for just about anything. They also have a low-cost line of stamped steel tanks than can accept the ZL1 fuel module for some popular musclecar era GM chassis. Call them for availability. Ricks
Precision Stainless and Fabrication: PSF supplies custom tanks for Roadster Shop, Detroit Speed, and many other custom shops and distributors for muscle cars, hot-rods, and most any other application. PSF
Want to tackle a tank yourself? You’ll need this part (installation guide near the bottom of the page for each ring type): Mounting rings