The LT4 Engine – A Need For Speed
Since the dawn of the automobile – and most especially, the sports car – automotive engineers and enthusiasts alike have worked relentlessly to increase horsepower, engine efficiency and, ultimately, 0-60 and quarter mile times both on and off the track.
For its own part, Chevrolet has been a pioneer of this endeavor. Since its inception in 1911, the company has pioneered engine technologies and has remained an innovator in producing some of the most powerful and most reliable engines ever.
Even before its introduction in 2015, General Motors engineers claimed that they had created one of the lightest and most compact 650 horsepower engines in the history of the brand, and implanted it in the fastest production Corvette ever built – the seventh-generation C7 Corvette Z06.
The engine in question? The all-new fifth-generation LT4 engine – a supercharged 6.2-liter V-8.
The Original LT4 Engine
The LT4 engine has always been synonymous with high-performance. Introduced by General Motors in 1996, the LT4 was specifically designed as a more powerful variant to the next-generation LT1 engine previously introduced by GM in 1992.
Although based on the LT1, and while sharing the same engine block and many of the same bolt-ons, the original LT4 featured a number of improvements that resulted in increased horsepower and an overall reduction in weight.
To start, the LT4 received newly designed aluminum heads, which featured larger intake and exhaust ports with bigger radius bends. The short-side radius of the LT4’s exhaust port was specifically increased in size to reduce back pressure at higher RPM’s.
In addition to the heads, the LT4 also featured a slightly more aggressive camshaft profile that increased duration from 200 degrees to 203 degrees (on the intake side) and 207 degrees to 210 degrees (on the exhaust side) and a high-flow intake manifold with taller ports (to accommodate the new head design) and bigger valves; 2.00-inch intake valves and 1.55-inch exhaust valves. Each of these valves were manufactured with hollow stems that were specifically designed to reduce weight. The exhaust valves were filled with sodium and potassium to improve heat transfer.
Revised valve lift specs called for 0.476 inch of lift on the intakes and 0.478 inch of lift of the exhaust. To help with the increased lift, each valve received special oval-wire springs that could handle the increased seat pressure without binding.
Additionally, Chevrolet employed the Crane Company to provide higher ratio (1.6:1) roller rocker arms. These roller rocker arms reduced friction measurably, thereby increasing economy and responsiveness. Each featured a roller tip.
Other refinements to the LT4 included a roller-type timing chain, a refined crankshaft, camshaft, water-pump, driver gear and main bearing gaskets to help bolster horsepower and accommodate the additional engine compression – which increased to a ratio of 10.8:1, which was a noted increase over the 10.4:1 compression found in the engine’s LT1 counterpart.
How Much Horsepower and How Many Were Made?
The LT4 was officially rated at 330 horsepower when introduced in the 1996 Chevrolet Corvette Special Edition models. Many Corvette enthusiasts have since tried to debunk the horsepower rating, claiming the General Motors intentionally underrated the engine’s true power potential. However, nobody has officially substantiated the claim and, until this day, there is still considerable debate amongst LT4 enthusiasts about the engine’s true capabilities.
Most claims place the engine’s output at somewhere between 340-360 horsepower (at the crank), though some extreme claims allege that their LT4 equipped Corvettes have been dyno’d at close to 400 horsepower!
Regardless of these claims, the intention of the LT4 engine – from its very inception – was clear; create an alternative that could provide drivers with a high-performance engine that resulted in a more track-capable Corvette.
Chevrolet succeeded in this venture with the inclusion of the LT4 engine in all 1996 Corvettes – including both the Collector’s Edition and Grand Sport Models – when equipped with a manual transmission. It seemed reasonable that “serious drivers” would select a manual transmission for their cars, and so a prospective buyer could only get the higher-horsepower engine in their Corvette if they also purchased it with the standard transmission.
Unfortunately, just over 25% of the Corvettes sold in 1996 came paired with the LT4 engine and manual transmission. With an all-new Corvette slated for the following model year, the LT4, while a vast improvement over any other engine introduced during the twelve-year run of the fourth-generation C4 Corvette, would not return for its sophomore year, except in a limited production of 1997 Chevy SLP/LT4 SS Camaros (106 in all) and Pontiac SLP/LT4 Firehawk Firebirds (29 in all.)
The Gen V LT4 – GM’s Most Powerful Production Engine Ever
Fast-forward nearly twenty years to the current-generation C7 Z06 Corvette, and you’ll find an all-new iteration of the LT4 engine. Introduced in 2015, the fifth-generation LT4 engine builds on the design strengths of the previous L29 supercharged engine that was used in the sixth-generation Corvette ZR1.
Additionally, just as the earlier LT4 engine pulled from technology introduced in the LT1, the current iteration of the engine also leverages technologies previously introduced in the all-new LT1 – a 6.2 liter, naturally aspirated engine – that was introduced in 2014 with the unveiling of the C7 Corvette Stingray.
The new LT4 engine utilizes the LT1’s direct fuel injection, Active Fuel Management (cylinder deactivation) and continuously variable valve timing, while also introducing several unique features designed to support its higher output and greater cylinder pressures created by forced induction.
The LT4 engine features Rotocast A356T6 aluminum cylinder heads that are stronger and capable of handling heat better than conventional aluminum heads. It also comes equipped with lightweight titanium intake valves, forged powder metal steel connecting rods, forged aluminum pistons, stainless steel exhaust manifolds, an aluminum balancer and a standard dry-sump oil system with a dual-pressure-control oil pump.
Supercharging for low-rpm torque and high-rpm horsepower
The LT4 also advances the supercharging technologies introduced and established with the previous-generation Corvette ZR1’s LS9 engine. A new R1740 TVS 1.7L supercharger features a pair of four-lobe rotors, each with a 160-degree helix (twist) designed to enable more torque production at lower engine RPM and sustain boost at higher RPM for greater horsepower.
The supercharger/intercooler assembly is more compact which helps the Corvette maintain its low hood profile. The supercharger is also 20 pounds lighter and spins faster – up to 20,150 RPM (which is 5,000rpms faster) – than the supercharger found on the previous LS9 engine.
“The LT4 Small Block delivers the ultimate horsepower and torque for the most capable Corvette ever,” said Jordan Lee, chief engineer and program manager, GM Small Block Engines. “Its tremendous low-end torque, enabled by a more efficient supercharger, maximizes responsiveness for a driving experience that is on par with the world’s most exotic supercars – with impeccable manners that make it suitable for daily driving.”
“The LT4 is only one inch taller than the naturally aspirated LT1 engine,” said Lee. “Along with a lower profile under the hood, the new, very compact supercharger helps the engine make power more quickly – and perhaps more importantly, it helps produce more torque earlier in the rpm band.”
Dry Sump Versus Wet Sump
The LT4 engine was initially developed to allow GM to introduce a higher-performance engine into its sports car brands – most especially the Chevrolet Corvette and Camaro. However, it was also identified quickly that the high-performance LT4 would provide automotive enthusiasts with a powerplant that produced plenty of horsepower while still being compact enough to fit into almost any vehicle.
For the 2015 Z06 Corvette, a dry-sump variant of the LT4 engine was manufactured. A “dry sump” engine simply means that the oil pump, storage (pan or canister) and oil filtration system can reside anywhere in the vehicle, thereby reducing the size of the conventional oil pan at the bottom of the engine.
This reduction in pan size allows the engine to be placed lower into the body of the vehicle, thereby lowering the car’s center of gravity. This translates into greater stability during extreme driving conditions. It also enables designers to lower the profile of the car, giving the vehicle a more aggressive, streamlined aesthetic.
Given the success of its design, General Motors quickly recognized that consumers would want to purchase the LT4 engine for vehicle projects beyond the Z06 Corvette. In a world where LS swaps in Ford Mustangs has become the norm, GM realized that the LT4 engine could provide enthusiasts at all levels with a high-performance small-block that could meet the needs of almost any project car.
The dry-sump variant of the LT4 engine can be purchased directly from General Motors. The GM Factory Part number is 19332702, and the engine features the same 650 Horsepower @ 6,400 RPM and 650 LB-Ft of Torque @ 3,600 RPM as the engine installed in the Z06. However, like the Z06 itself, this engine comes with a hefty price tag. The LT4 dry-sump engine has an MSRP of $16,819.00.
Despite the big-dollar price-tag, serious automotive enthusiasts recognize the engine for its tremendous raw power, its “exceptional capability in a more efficient package.” In addition to the Chevy Corvette, the dry-sump version of the engine is also available in the third-generation Cadillac CTS-V, as well as the 2017 Camaro ZL1.
Like its Dry-Sump counterpart, General Motors also offers consumers the option of buying the slightly more conventional Wet-Sump configuration of the LT4 engine.
This engine, which features a traditional oil pan in lieu of the more-radical dry-sump oil solution, features slightly less power output than the other LT4 variant. The current Wet-Sump version of the LT4 engine can be ordered from General Motors under factory part number 19332621.
The wet-sump version of the LT4 boats 640 horsepower @6,400 RPM and 630 LB-FT of torque @ 3,600 RPM. With an MSRP of $16,172.00, the engine is $647.00 cheaper than its dry-sump counterpart, but the added value of a conventional oil system also enables the engine to be more readily installed in any project car without the need to relocate the oil delivery/storage system.
The tradeoff of this convention is that the engine does have a slightly higher profile than its dry-sump counterpart. Still, for most muscle cars, this added clearance height should pose no issue, while the output of this small-block beast will provide drivers with white-knuckle power in a small-block design.
So Why Purchase an LT4 Engine?
Consider that very few small-block engines on the market today – that few engines of any sort on the market today for that matter – are capable of producing the kind of horsepower and torque that the LT4 can.
To achieve 650-plus horsepower, automotive designers, builders, mechanics and enthusiasts of all classifications have invested considerably more into building their engines – often with the inclusion of significant internal engine work combined with turbo/supercharger bolt-ons – to accomplish this feat.
While there are a number of engine modification kits available aftermarket, these modifications often produce other mechanical challenges – from spun bearings to cracked engine blocks, (or even worse) – for the would-be “weekend warrior.”
Instead, GM has presented a solution that enables consumers to make an investment in an engine program that provides a properly balanced, properly fortified engine that can be installed into almost any engine bay in almost any car – and transforming its recipient into a vehicle with supercar performance without the compromise of adding bolt-ons to a factory block that may not be able to endure the stresses placed upon it.
The LT4 certainly keeps great company. Consider that the list of current production engines producing 650-plus horsepower is short and distinct – and that each has a price point that makes the LT4 look like an incredible value: The Hellcat Hemi V-8 from Dodge has a base MSRP of $21,355.00, Ferrari’s V-12 engine (found in the F12 Berlinetta, the FF and the LaFerrari) sells USED for more than $24,000.00 (we could not get pricing on a new engine), the Lamborghini Aventador’s V-12 engine (price unavailable), the Bugatti Veyron’s W-16 (price unavailable) and McLaren P1’s twin-turbo V-8 engine (price unavailable.)
While there are certainly other powerplants available on the market today that can out-perform the LT4 engine, there are few that can rival the power and performance out of a small-block engine. Moreover, there are even fewer options out there that can provide the amount of power and performance for the price.
When put together, there is no question that the LT4 engine is one of the most impressive engines on the market today….and naturally, it made its debut as the heart of a Corvette.