Turning A Supercharged LT5 Engine Into A Hybrid LT/LS Combination

Engine swaps have been the backbone of hot rodding since the first flathead V8 hit the market in 1932. Back then, the new-fangled powerplant confused many and excited most. Here we are, jumping into 2022, and once again, a new engine is confusing many and exciting most. Enter Chevrolet’s newest iteration of the LT engine, the supercharged LT5. Okay, okay, Chevrolet did introduce an LT6, but the architecture is vastly different, so…

A Little Bit About The LT5

This latest LT engine was introduced to the masses in 2019. Chevrolet unleashed this monster that delivers a supercharged 770-plus horsepower and a new direct injection fuel system. The new LT5 employs a high-pressure fuel system delivering approximately 2,100 psi to squeeze fuel directly into the combustion chamber. This exorbitant amount of pressure requires the use of a mechanical fuel pump. The LT5 fuel mover functions via a camshaft-driven fuel pump. This is GM’s first dual-fuel injection system, employing a primary direct injection and a supplemental port injection.

When the LT5 is experiencing low RPM operation, the engine relies upon the standard direct injection. When under high load, the secondary port-injectors are activated. This serves as GM’s first use of a dual-stage fuel system in any production automotive engine. This “dual fuel” system helps the supercharged LT5 achieve an output of 755 horsepower and 715 lb.-ft. of torque.

LT5

The supercharged LT5 is a technological marvel. However, there are still a few traditional hot rodders that like the idea of a modern mill with a traditional look. Hence this LS/LT combination.

Adding direct injection required a serious change in cylinder head design. Fuel is introduced via injectors that are now located between the intake and exhaust valves, directly opposite of the spark plug.

The latest LT also uses a taller valve angle of 12.5 degrees instead of a traditional small block’s 23-degree valve angle. Another design upgrade is the extremely large intake ports that are closer to a square when compared to the Gen IV’s rectangle orientation. The exhaust ports are symmetrically spaced and exit in roughly the same relationship to the Gen III/IV heads. However, the Gen V bolt holes are in a completely different location.

Previous generations of LT (and LS) engines utilized a relatively conservative valve timing, but with the introduction of variable valve timing (VVT) on Gen-V engines, more duration is able to be utilized. VVT affords the ability to advance the camshaft at lower engine speeds to regain power that might have otherwise been lost with longer intake or exhaust duration specs. Having VVT can retard the position of the camshaft by several degrees and add even more power at the top end.

Hot Rodding The Newest LT

With all of these high-tech features and design changes, what does that mean for intrepid hot rodders wanting to use the latest LT engine as a basis for swaps? For starters, a lot of work — especially since GM has discontinued the LT5 crate engine program that comes with the requisite controllers. Now, a swap like this means finding a complete drivetrain in a wrecked vehicle to undertake the task — or does it.

LT5

To simplify the engine management, the VVT was locked using Comp Cams' Lockout kit (PN: 5465) and ICT Billet’s Cam Sensor adaptor harness (PN: WA CAM41-6). Even though the need for an OE-style ECU has been eliminated, the ignition system still needs to be controlled. To handle that task, an MSD 6LS box (PN: 6014) is implemented.

Recently, we learned the guys at United Speed World (USW) in Tampa, Florida, were putting together a combination they dubbed the LS/LT. According to Phillip (Junior) Joyner Jr, “we have a customer that wants to utilize the latest GM engine but also wants to simplify things by adding a carburetor.” We’ll give you a moment to return your lower jawbone to the up and closed position.

While we are certain many of you will question the idea of proactively “dumbing down” such a technologically advanced engine, there are apparently some who feel it is okay to undertake the simplification. How many remember the cries of blasphemy when the first carbureted LS intake was released? Regardless of your lower jawbone location or opinion about the change, what is involved in actually completing the task?

Making The LT5 Breathe Naturally

For starters, the top end needs to be replaced. This is the area that would be the most complex to make operational. This means a new intake system, eliminating the supercharger. There is no EFI-capable intake system (without a supercharger) on the market for an LT5, so how does one overcome that obstacle? In this case, the engine’s owner actually wants to incorporate a carburetor. However, there is no carburetor-ready intake available as well, so how can the engine be simplified? I’ll dive deeper into that a little later.

A major hurdle that needs to be “controlled”, is the LT5 dual fuel delivery system. The complexity at which the fuel systems work in unison is not easily overcome without a controller. As of this writing, OE versions are unbelievably difficult to obtain. There are aftermarket offerings like the Holley Terminator X, but again, this is an exercise in “what if”, and a carburetor will be fueling the fires.

To get an LS intake to fit the LT heads, an ICT Billet adaptor is needed.

Since the customer actually wants to employ a carburetor, that means a new intake is needed. Whether unfortunate or not, you will not find a carburetor-style intake for a new Gen-V LT engine. I know, I know, why would anyone want to put a carburetor on a late-model engine? Simply put, he feels like it. It’s his engine and that’s what he wants. It does, however, present a concern about how to bypass the “dual-fuel” system already in place.

The intake to be used is Holley’s LS3 carburetor-ready intake (PN: 300-291-BK). Since USW is actually building an LT5 and not an LS, this presents a hurdle. An LS intake will not physically bolt to the Gen-V LT engine. To address the connection of the LS intake to the LT heads, United Speed World needed adaptors. Luckily, ICT Billet makes the right intake adaptors (PN: 5551347-LT-LS3) to make the merging of parts work.

LT5 Dyno

In supercharged form, the LT5 makes 770-plus horsepower. By removing the induction system and adding a carburetor, the pump-gas friendly 10.0:1 compression ratio delivered a respectable 501.6 horsepower at full song.

Because the dual-fuel system will be eliminated and removing the factory intake still leaves a set of injectors integrated with the cylinder heads, a solution was needed. At first, USW thought about leaving the injectors in the cylinder heads and utilizing them simply as plugs for the holes. But just having a set of injectors protruding from the cylinder heads is unsightly. The fix is to use a set of Motion Raceworks injector delete plugs (PN: DI-P) and ICT Billet’s delete plug hold down brackets (PN: GENV-FPP-FLP-DELETE).

LT5

Motion Raceworks injector plugs and ICT Billet plug hold-downs replace the LT5 injectors in the cylinder heads.

The LT5 Gets A Cooler Idea

While the cooling system on the LT is more than adequate, the owner of this iteration decided he wanted to clean up the front of the engine. In stock form, the LT has an offset water pump and a bulky accessory drive that holds the alternator, A/C compressor, and several idler pulleys. Now, however, the engine is not required to support niceties like an A/C compressor, power steering pump, or other accessories.

Removing the LT water pump and replacing it with a pump from an LS actually centers the pump at the centerline of the engine and is accomplished via Dirty Dingo adaptors.

An LS water pump and accessory drive are employed to give the front of the engine a clean look. “The LT water pump is awkward and complicated, while the LS pump is centrally located,” says Phillip Joyner Jr. of United Speed World.

LT5

Again, you are probably wondering why the owner took a perfectly good, supercharged engine and “traditionalized” it by removing the blower and EFI and replacing it all with a carburetor? Consider this an endeavor in “what if.” Just like the LS did many years ago, the LT engine will soon be finding its way into an untold number of classic rides. Also, like the LS, many of those soon-to-be realized swaps will buck technology and involve a simplified install. Frankly, that’s alright by us.

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About the author

Randy Bolig

Randy Bolig has been working on cars and has been involved in the hobby ever since he bought his first car when he was only 14 years old. His passion for performance got him noticed by many locals, and he began helping them modify their vehicles.
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