Let’s Talk 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 new LT5 has just arrived, and we’ll wait to see what GM recommends for fueling before diving too far in.

UPDATE! VaporWorx now has a new controller to handle the increased fuel demand for modified LT4 and stock+ LT5! Click here to view it.

High and Low Pressure Fuel Systems

The first thing to remember about these new direct injection (DI) engines is that they are no more difficult to feed fuel to than an LSx/Gen4 engine. The part that throws some folks off is that GM refers to the High Pressure Fuel and the Low Pressure Fuel systems.

In linear fashion…

Low pressure fuel system High pressure system / mechanical pump Direct Injectors

The high pressure pump is 2000+ psi, far higher than an electric fuel pump 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 fuel system / 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 fuel module well, but it does not have sufficient power capability support multiple fuel modules.

Previous GM FSCM’s also could not handle any significant additional power (two fuel modules, upgraded pumps, voltage boosters, etc.)

All of the aftermarket engine controllers 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 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 50-55psi 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/, 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, exactly 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.

Since the LT5 was supplied only in the C7 ZR1 there is no single fuel module that will supply enough fuel unless the C7 part is used. However, the C7 part is very tall, over 14″, and does not fit many chassis. In that light, dual Gen5/6 fuel modules will provide sufficient gasoline or E85 fuel to meet the LT5 demand. If having long-term OE reliability, returnless, no external filters, etc. is the goal for the car, then dual Gen5/6 ZL1 fuel modules are highly suggested.

UPDATE Dec. 2022: VaporWorx now has an all GM fuel module that will handle the power needs of the LT5, and work well for most all other applications using the Gen5 ZL1 setup. If you’re looking at adding power in the future, this may be a good option: https://www.vaporworx.com/shop/product/gen5-camaro-zl1-super-fuel-module/

Let’s do some math…

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 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.

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 the LT1 and stock LT4 engines, the Gen5 and Gen6 Camaro ZL1 or CTS-V3 fuel modules will work well. The Gen6 Camaro and CTS-V3 are the same part. For most musclecar chassis the Gen5 ZL1 – GM Genuine MU2101 is the best choice since it is significantly shorter.

The pumping sections of the Gen5 ZL1 and Gen6 ZL1 Camaro are sufficient for the LT4, so choose the pump that suits the chassis/tank the best.

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 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. Deatschwerks has a high pressure pressure relief valve to increase the system pressure (also available from VaporWorx/please call.)

For LT1 up to 750HP naturally aspirated, the Gen5/6 ZL1 pump will work well.

For stock LT4, the Gen5/6 ZL1 module will work well. It’s what came in the OEM application.

For higher output LT4 up to 750hp, the VaporWorx Super ZL1 fuel pump can be used. https://www.vaporworx.com/shop/product/gen5-camaro-zl1-super-fuel-module/

For stock LT5, the VaporWorx Super ZL1 fuel pump can be used. https://www.vaporworx.com/shop/product/gen5-camaro-zl1-super-fuel-module/

Adding more power (750hp+) or E85 to the LT4 and LT5 can become a problem. There is not off-the-shelf OEM fuel module that will meet the 750hp+ demand without a voltage booster. The suggested option in these cases is to use twin ZL1 fuel modules . This has shown to be an excellent system for street, autocross, and road course duties for up to 900hp E85.

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:

1) Twin fuel modules has shown to work well. However, the GM FSCM alone likely is not going to work. It will become overloaded. VaporWorx has a dual fuel module controller for these needs. This is especially true if E85 is used. E85 requires 30% more flowrate than gasoline.

2) A voltage booster. However, the input voltage to the GM FSCM is typically limited to approximately 16.5v or else the system will throw malfunction indicator codes. The VaporWorx fuel module controller can accept up to 22v with no issues. A rough estimate is that for every volt of change, there is a corresponding 15% change in pump performance up to approximately 18v.

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. VaporWorx has several option to make these swaps easier, available in our LT Engine Installation Parts section.