Debuting alongside the then-new seventh-generation Corvette in 2014, the LT series of General Motors’ small-block V8s brought with them an array of advanced tech that trumped the outgoing LS engines in terms of performance, emissions, and fuel efficiency. While LS motors have long since established themselves as cornerstones of the performance realm, both in factory form as well as becoming the go-to mills for big power swaps in tight confines, the march of technology (and federal regulations) demand that manufacturers implement new solutions to stay ahead of the curve.
Among the multitude of changes that differentiate LS and LT series engines, the latter’s transition to direct injection from the more traditional sequential multi-port fuel injection setup found in the former mill offers improvements across the board in stock factory form, benefiting both enthusiasts and efficiency-conscious drivers as well. Considering the range of different vehicles these LT motors are now installed in – everything from garden-variety full-sized GM trucks and SUVs to supercharged ground pounders like the Corvette Z06, Camaro ZL1 and Cadillac CTS-V, it’s quite a balancing act to keep every driver happy.
Direct injection might be the most obvious differentiator of the LT1 and LT4 (seen here respectively) and their LS-based counterparts, the LS3 and LS9, but it's important to note that the LT series engines' direct-injection system also has a significant effect on the design of various components throughout both motors. This includes the camshaft used in each, which have a tri-lobe located at the rear of the cam that drives the mechanical fuel pump required by the DI system. Images: General Motors
Enthusiasts are a group that can be particularly hard to please – no matter how much power a car comes with from the factory, somebody is going to want more. For LS projects, this hasn’t been much of an issue in recent years, as a healthy aftermarket has made adding power to LS engines a no-brainer for the most part.
Like the standard ZL1, the recently announced 2018 Camaro ZL1 1LE will pack a supercharged LT4 to go along with its track-focused suspension, aero, and tire package. Image: General Motors
But the relative newness of LT engines and their comparatively exotic tech equates to less currently available aftermarket options for builders who want to add a substantial dose of grunt to their LT motors. The limitations of direct injection, in particular, often serve as a bottleneck in the pursuit of over-the-top power for LT projects.
While there’s a few different ways of addressing the issue by adding supplemental fuel sources like water-meth injection systems or auxiliary port injection systems, Lingenfelter Performance Engineering has responded to enthusiasts’ demand for additional fuel flow capability in LT motors with a solution that retains both the general design of the factory fuel system as well as factory-like drivability with their new High Flow Direct Injection Kit for GM’s Gen V V8s, a group of Lingenfelter-developed components that comprehensively upgrade the factory fuel system to provide enough juice to bring gasoline-powered LT builds well into four-digit horsepower territory. Here we’ll go over the inherent limitation LT builders face with the factory direct-injection system and get the low down on this new kit from the folks at Lingenfelter to see how they’ve addressed those issues.
New Tech, New Challenges
When working with typical port-injection systems, upgrading the flow capacity is a fairly straight-forward proposition involving fuel pump and injector upgrades, along with the requisite ECU tweaks to ensure that the motor knows what to do with the additional fuel. The equation is a bit more complicated with direct injection though.
“With the General Motors setup, you have several factors to consider,” says Lingenfelter’s Jason Haines. “The first limitation most folks run into is with the electric in-tank fuel pump. Normally just moving to a bigger pump would be the solution here – that’s an issue that enthusiasts have had to address for a long time. However, with this system, there’s also a cam-driven mechanical fuel pump, and that poses a bigger issue because of how direct injection functions.”
Tucked away under the intake manifold of the LT1 seen here is the direct injection system, which consists of a cam-driven mechanical fuel pump that’s hooked up to a set of injectors that spray fuel directly into the combustion chamber (hence the name). Because of the implementation of direct injection, the cylinder head design is significantly different than that of the LS3 as well, as the injector, spark plug and valve locations have changed to accommodate the new system. Image: General Motors
The first limitation most folks run into is with the electric in-tank fuel pump. Normally just moving to a bigger pump would be the solution here – that’s an issue that enthusiasts have had to address for a long time. However, with this system there’s also a cam-driven mechanical fuel pump, and that poses a bigger issue because of how direct injection functions. – Jason Haines, Lingenfelter Performance Engineering
While the in-tank electric fuel pump operates at about 58 psi, the LT motors’ direct-injection system calls for very high pressure fuel delivery, which means the LT1’s mechanical fuel pump operates at about 2,200 psi while the LT4 pumps out fuel at about 3,000 psi. And since the mechanical pump is driven by the camshaft, the amount of fuel it can deliver at any given moment is highly dependent on engine RPM.
More importantly, the combustion process is fundamentally different with a direct-injection system. “With a typical port-injection system, you essentially have the entire pulse width range to work with because the intake valve controls the timing of fuel delivery into the combustion chamber – that can be as much as 19 milliseconds,” Haines explained. “But with a direct-injection system, you can’t fire the injector in 100 percent duty cycle like you can with port injection – you can’t keep spraying while the intake valve is closed – so you have a much smaller window of time to fire the injector. For direct-injection injectors, you will rarely make it above 6 to 6.5 milliseconds before you start seeing misfires.”
Since the injector is after the valve in a direct injected setup, valve timing has no control over the combustion process. Accordingly, a larger injector is needed that can deliver the required fuel during that brief window of time in order to provide the juice when it can be utilized by the engine.
Lingenfelter’s Three Part High-Flow Solution
So, we’ve established that the LT motors’ direct-injection system limitations boil down to essentially three main concerns – fuel displacement from the mechanical fuel pump, that fuel pump’s flow capacity throughout the rev range (which is partially dictated by the camshaft design that operates it) and the injectors that deliver the fuel under high pressure. Accordingly, Lingenfelter’s kit addresses all three elements with components that are designed to work in harmony to substantially improve the fuel flow capability without resorting to auxiliary fuel delivery solutions.
While an auxiliary-port injection system can bring additional fuel capacity to LT motors, they also add quite a bit of complexity as well, and Lingenfelter is quick to point out that every component added is another potential part that can fail. Considering the fact that such would require additional fuel lines and possibly a second tank (along with significant ECU tweaks), that’s something worth taking into consideration. Rather than supplementing the stock system, Lingenfelter’s solution simply replaces the limited capacity stock components with high flow pieces of their own design.
“Auxiliary systems like supplementary port-injection and water-meth injection systems can be effective, but they add a substantial amount of complexity,” says Haines. “With an auxiliary-port injection system you’ll need to add an extra tank or plumb the factory tank and add an auxiliary controller, and the production ECU won’t know what to do with the extra fuel. If the computer doesn’t know about the auxiliary system it’s going to fire the injectors for too long, which will cause unstable combustion, so significant ECU changes would be required to get the system to run properly.”
“Water-meth injection systems face similar issues,” Haines added. “The biggest issue is ensuring that the electronics know how to properly deliver the fuel. And of course, every extra part added with systems like these is another piece that can fail, since these solutions don’t use the stock fuel system and lines.”
Designed for turbocharged and supercharged engine applications running either gasoline or E85, Lingenfelter’s kit addresses the limitations of the factory components rather than supplementing them with a secondary source.
Lingenfelter's 22 gram/second high-flow injectors deliver 24 percent more flow than factory LT4 injectors, 44 percent more than the LT1's stock injectors, and 80 percent more flow than production injectors used in the L83. Built and tested to OEM specifications for durability, these injectors are E85 compatible and are flow tested and matched as a set.
On the injector front, the kit utilizes a set of eight flow-matched 22 grams/second direct injection fuel injectors that feature Lingenfelter’s patented K-DI kinetic nozzle geometry, which provides high flow rates without sacrificing atomization. The injectors actually spray two streams of fuel at one another, as they exit the injector, in order to atomize the fuel completely. This allows the injectors to produce a specific spray plume shape that’s matched to the combustion chamber and intake charge motion of GM’s Gen V V8 engines, which means they’re built to perform efficiently from low RPM, light-load conditions all the way to peak power at high RPM. Tested to meet OEM durability and performance specifications, these injectors provide 24 percent more flow than the factory LT4 injectors, 44 percent more than the stock LT1 injectors, and 80 percent more than the standard injectors found in the 5.3-liter L83 V8.
The packaging constraints of the direct injector required Lingenfelter to turn to the experts at Nostrum in order to develop an injector that would physically fit in the stock location but provide the additional fuel necessary for high-horsepower applications. Nostrum is currently one of the only manufacturers that have figured out how to increase the injectors’ flow capabilities while retaining the stock sizing and operation.
Nostrum K-DI injectors offer plume angle ranges from 35 to 110 degrees and plume targeting angles from 0 to 35 degrees, enabling cleaner, more efficient combustion to produce more power safely and with control. While Bosch and other injector companies may be hot on their heels, for now Nostrum is the go-to provider for all thing pertaining to direct injection on the LT series of engines.
In addition to the in-tank electric fuel pump, there’s also a mechanical fuel pump that delivers the juice to the high-pressure injectors in GM’s direct-injection system. While it looks like a stock unit externally, Lingenfelter’s 12.0mm big bore pump delivers nearly 10 percent more fuel flow than the stock LT4 fuel pump and over 30 percent more than the factory pump used with the LT1 and L83. Since it is cam driven, its output is proportional to engine speed, and the camshaft’s lobe design affects the pump’s flow rate as well. That’s one of the reasons why Lingenfelter suggests pairing it with their GT35 camshaft to get the full benefit of the upgrade.
“While the stock LT1 fuel pump is a 10.5mm bore and the LT4’s is 11.5mm, our high flow pump is 12.0mm,” Haines explained. “These pumps operate much like a piston engine in that increasing the bore in turn increases their displacement – the Lingenfelter pump displaces almost 10 percent more fuel than the stock LT4 pump and over 30 percent more than the LT1’s.”
These pumps operate much like a piston engine in that increasing the bore in turn increases their displacement – the Lingenfelter pump displaces almost ten percent more fuel than the stock LT4 pump and over thirty percent more than the LT1’s. – Jason Haines, Lingenfelter Performance Engineering
Lingenfelter says these pumps have been tested to provide enough fuel flow for more than 1,100 horsepower on a turbocharged, gas-powered LT4 build and over 900 horsepower on the same mill running on E85.
While this high-flow mechanical fuel pump is compatible with production LT1 and LT4 fuel pump lobes (i.e. the stock camshaft used in those motors), since it is cam driven, the pump’s true capability is only realized when pairing it with a camshaft that’s designed to utilize its flow capacity. “Half the flow increase in this kit comes from the camshaft,” says Haines. “For instance, if you’re trying to get an LT1 to have the flow capability of an LT4, just swapping the pump won’t do it – the camshaft is the other element of the equation and you need both to get the full benefit.”
And that’s one of the main reasons why Lingenfelter’s GT35 camshaft is the third component of this kit. “This cam is designed for supercharged and turbocharged applications and is an upgrade over the stock LT4 camshaft,” Haines told us. “It offers more duration and lift, and while you can use it with the stock cylinder heads, you’ll see even more gains with ported heads since the design is tailored toward them. The same goes for the fuel pump – this cam will work with the stock pump, but you’ll get a more significant benefit if it’s paired with the high flow unit.”
Designed for forced induction builds, Lingenfelter’s GT35 camshaft is an upgrade over the stock LT4 cam but can be used with LT1 and L83 motors as well. Increases in duration and lift allow more fuel to be delivered without any sacrifices in drivability. That means this cam will provide performance gains even if you stick with the stock mechanical fuel pump, though like the other components detailed here, it works best when functioning in tandem with the other upgrades in the Lingenfelter high-flow kit.
The overall theme is that while each of these components is available to customers individually, they’re designed to work in concert with one another and the full benefits of each part are realized when the cam, pump, and injectors are utilized together.
How much of a benefit, you ask? Take a look at this dyno sheet Lingenfelter provided, which shows a pull on a turbocharged LT4 with stock compression running on VP 109 race gas:
Those looking to add serious performance to their LT builds quickly discover that the stock fuel system’s capacity is a major bottleneck on the path to 1,000+ horsepower – it can’t handle much more than what the stock LT4 asks of it. Rather than adding the complexity of a supplemental system, Lingenfelter’s solution addresses the shortcomings of the factory DI components. Since the pump is cam driven, this turbocharged LT4 is dialed in to deliver peak fuel capacity at higher RPM to avoid running out of capacity low in the rev range. “If you’re fuel limited and you want to make a big horsepower number, you need to design the build to make the power at the top end because you run the risk of running out of fuel at lower RPM otherwise, and turbos help to address this to some degree by allowing you to adjust where the boost comes in,” Haines said.
But if 1100+ horsepower still isn’t enough for you and your LT-series build, don’t worry, Lingenfelter says there’s even more potent options on the way. “We are currently developing and testing even higher flow mechanical pumps and injectors,” Haines said. “These will be designed mainly for street and competition vehicles that are still running the stock ECM controls. The main factor behind developing these is because there are folks running E85 who want horsepower levels where the gasoline builds are now, which will require about 30 percent more fuel to get there.”
Does four-digit horsepower in your LT-powered GM vehicle sound appealing to you? Lingenfelter Performance Engineering has been dialing serious performance into GM vehicles for more than four decades – give ‘em a shout and find out what your direct injected ride is really capable of.