Chevrolet's latest and greatest small block is the Gen V LT-series. We dive into the engine architecture, its high-tech intricacies, and all of the pistons we've designed for this power-dense platform.Over the last decade, the fine fellows at General Motors have embraced many different forms of technology to improve the small-block engine platform, culminating in the current-day Gen V engines powering a wide range of the General's performance machines.
There are a few different styles of Gen V engine, starting with the L83 5.3-liter engine available in the light-duty GMC and Chevrolet pickups. It uses a 3.80-inch bore and 3.622-inch stroke to achieve its displacement. Configured as such, the L83 engine develops 355 horsepower and 383 lb-ft of torque.
The naturally aspirated LT1 6.2-liter engine is factory-installed in the 2014-present Corvette Stingray and the 2016-present Camaro SS. With 455 horsepower and 460 lb-ft of torque on tap, this engine configuration provides plenty of motivation for the performance enthusiast. Taking advantage of current engine technological advancements, the LT1 offers 11.5:1 compression and many other modern tricks designed to improve power, performance, and perhaps most importantly, fuel economy. With ever-tightening federal regulations up in the air, GM's engineers nevertheless continue to focus on incremental improvements in the engine's overall capabilities.
But the company didn't stop there; the supercharged LT4 engine is based on the LT1, but with the addition of the 1.7-liter Eaton TVS supercharger on top, a nice, square 650 horsepower and 650 lb-ft of torque is available to the driver's right foot in the 2015-current Corvette Z06 and ZL1 Camaro, while the slightly-more-refined Cadillac CTS-V receives 640 horsepower and 630 lb-ft of torque.
Then you have the big-dog LT5, which is the engine featured in the Corvette ZR1 and could be considered the ultimate small-block Chevrolet engine ever produced by the factory. With 755 horsepower underneath the shaker hood, the all-new 2.65-liter TVS-based supercharger, and nearly 14 psi boost pressure at full song, the LT5 is clearly the king of Gen V LT engines.
In all configurations, the engine is designed around an aluminum block and cylinder heads, with the bore size separating the L83's 5.3-liter spec from the LT1, LT4, and LT5's 6.2-liter blueprint.
Other modern technologies employed by GM to enhance performance in each of these engines include direct fuel injection, active fuel management, continuously variable valve timing, and piston cooling jets.
And if you're looking to improve the performance capabilities of your LT-based engine, then Wiseco Pistons has the solution for you.
“Currently we are servicing the L83, and Gen V 6.2-liter LT engine found in the Camaro, Corvette, CTS-V. and trucks. What we don’t make in a shelf piston we can certainly make in a custom,” says Vic Ellinger, Technical Sales Associate at Wiseco in Ohio.
Direct Injection Discussion
As one of the most significant engine technology advances of the last few decades, direct injection (DI) offers many performance benefits, most importantly with respect to emissions control and precise engine management. Both naturally aspirated and boosted engines take advantage of the technology, which must be accounted for during the process of developing a forged piston for DI applications.
Direct injection in the LT engine family is accomplished through the use of a high-pressure fuel pump, driven off three lobes which are machined into the camshaft. The pump supplies fuel at pressures up to 2,200psi , and delivers it into the combustion chamber. The fuel meets the piston at just the right time, and when combined with careful engine management calibrations, the injection of the fuel right into the piston tops ensures that the fuel vaporizes instantly in the engine.
This vaporization (instead of the atomization which occurs in a port fuel-injected engine as the fuel injector sprays into the port rather than the cylinder) occurs because of the shape of the piston top, which has been designed much like a bowl, and works to speed up the fuel vaporization.
Rather than reinvent the wheel (or piston in this case), Wiseco's engineers smartly deferred to the expertise—and millions of dollars in research and development—invested by General Motors during the development process for the original-equipment pistons.
“The bowl shape is very specific to each family of engines. Currently we do not disturb the original shape on shelf items,” says Ellinger. “The forging is a dedicated design that is made specifically to accommodate the unique DI bowl and LT valve reliefs. It is a strutted design that is very strong and relatively lightweight.”
The bowl shape on the LT engine family's pistons is located directly underneath the fuel injector in each cylinder, with another concave depression underneath the exhaust valve. This concave area is where the majority of the combustion occurs.
The main reason to mimic the factory design when it comes to the bowl shape and location is to simplify the tuning process as much as possible for these complex engines. If the tuner knows the engine's combustion is occurring as designed by the factory, this important variable is minimized as much as possible, helping to reduce the amount of time for the tuner to develop a calibration.
However, “On the custom side there are companies we have worked with experimenting with different designs especially with forced induction,” he explains.
Part Number Selection
There are twelve separate part numbers designed for the L83 platform, with four major selections tailored to different compression ratios and connecting rod length. There is a piston designed for the builder's choice of 9.50:1 or 10.50:1 compression ratios (measured with 58xcc chambers), with a choice of 6.098-inch or 6.125-inch connecting rod specification. These pistons are all designed for stock stroke applications, and 3.780-, 3.790-, and 3.800-inch bores are covered as well. Each L83 piston set is shipped with Wiseco's GNX piston ring package, which includes a 1.5mm gas nitrided, barrel-faced positive twist top ring, a 1.5mm cast iron, phosphate-coated, taper-faced under hook second ring, and a 3.0mm stainless steel three-piece oil ring design.
There are 14 separate part numbers available for the 6.2-liter engines, with 4.065-, 4.070-, 4.075-, and 4.125-inch bore, 3.622-inch and 4.00-inch stroke, and various compression ratios available. These pistons all use the GFX ring set from Wiseco, which features 1.2mm gas nitrided, barrel-faced positive twist top rings, a 1.2mm cast iron, phosphate-coated, taper-faced under hook second ring, and a 3.0mm stainless steel three piece oil ring design.
Certain applications include Wiseco's ArmorPlating technology as standard equipment; which is applied to the piston tops, ring grooves, and wrist pin bores, and is designed to protect against heat and detonation. The plating actually gains hardness when it is heated, which Wiseco's R&D Manager, David Fussner, says is extremely useful, especially on the top of the piston. It helps to reflect heat back into the chamber to improve combustion efficiency and allows the piston tops to run cooler as well, on the order of 20-degrees Celsius. It also helps to reduce carbon buildup on the piston tops, as the carbon effectively can't get a grip on the plating material.
Each of the Gen V LT pistons regardless of engine platform is forged from a 2618 high-strength alloy and makes use of .200-inch-wall pins and Spirolox for pin retention. In addition, anti-detonation and pressure seal grooves are machined into the forging.
Wiseco's ArmorGlide high-tech lubricant is applied to the skirt of each of these pistons; it is designed to reduce friction, but also allow the piston to be fitted more tightly in the bore than a non-coated piston. The reduction in piston-to-wall clearance has the benefit of better ring seal and reduced piston noise caused by the piston rocking in the bore. It remains bonded to the base material for the life of the piston, and the computer-controlled application process for the skirt coating ensures consistently reliable treatment to the piston skirt surface.
With the popularity of the LT engine platform starting to take hold in the performance community, Wiseco has positioned itself to provide enthusiasts and racers with pistons to improve durability, reduce friction, and improve performance across the board.