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LT2, LT6, And LT7

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  • #16
    If the LT2 is a stroked LT1, that would raise piston velocities at any given RPM. To increase both the stroke and the redline would probably require an upgrade of pistons to forged pistons, as used in the supercharged engines, I would think.

    More likely, some horsepower found in an exhaust system redesigned for mid engine application.


    • #17
      Also HP will be found in incorporating most of the engine efficiencies GM pioneered in its 2.7L new motor (first identified and shared thanks to JB). Not all of them of course (not turbo in the LT2 as just one example, but probably more than a few of the following:

      Originally posted by gmauthority
      GM 2.7 Liter I-4 Turbo L3B Engine

      The GM L3B is a turbocharged gasoline engine produced by General Motors for use in full-size pickup trucks. Displacing 2.7 liters in an inline-four cylinder configuration, the L3B is a clean-sheet design for General Motors. The engine was developed from the outset as a truck engine.


      The GM L3B engine made its debut in the 2019 Chevrolet Silverado 1500 and 2019 GMC Sierra1500 producing an SAE-certified 310 horsepower and 348 pound-feet of torque.

      The motor was developed specifically for truck applications, and the motor delivers peak torque from 1,500 to 4,000 rpm. Additionally, it makes 22 percent more torque than the 4.3L V-6 LV3 it replaces.

      “The new 2.7L Turbo is a technological marvel, with our most advanced valvetrain,” said Tom Sutter, chief engineer for the 2.7L Turbo. “With a broad, flat torque curve and quick throttle response, it punches above its weight, delivering surprising performance and efficiency.” Designed As A Truck Engine

      To help generate the strong low-end torque customers expect in a truck, it was designed with a long piston stroke of 4.01 inches (102mm), which is the distance the piston travels up and down within the cylinder.

      The long stroke enables improved combustion and thus a higher compression ratio. Typically, a long stroke can increase the load of the pistons against the cylinder walls, generating more friction. That’s alleviated in the 2.7L Turbo with an offset crankshaft. It is slightly off-center of the cylinders, allowing a more upright position for the connecting rods during their movement.

      To support the high cylinder pressures that come with turbocharging, the crankshaft and connecting rods are made of forged steel and the pistons are made of a tough aluminum alloy with a cast iron ring groove insert.

      All elements of the 2.7L Turbo were designed for the demands of turbocharged performance in a truck environment, and the engine was subjected to the same rigorous durability standards as the Silverado’s proven V-8 engines.

      The 2.7L Turbo features an aluminum block and cylinder head for reduced mass. Unique Valvetrain Offers More Precise Control

      The cornerstone of the 2.7L Turbo L3B is an innovative double overhead cam valvetrain that enables:
      • GM’s first use of Active Fuel Management (cylinder deactivation) on a four-cylinder engine.
      • High- and low-lift valve profiles.
      • Continuously variable valve timing.

      In fact, the innovative valvetrain is GM’s first to incorporate variable lift, duration and Active Fuel Management to optimize performance and efficiency across the rpm band. It is a key reason the engine’s peak torque is available at only 1,500 rpm.

      The system’s electro-mechanical variable camshaft effectively allows the engine to operate with three different camshaft profiles, complementing the variable valve timing system to deliver optimized operating modes for different engine speeds and loads:
      1. High valve lift for full power.
      2. Low valve lift for balance of power and efficiency.
      3. Active Fuel Management shuts down two of the cylinders in light load conditions to further conserve fuel.

      “It’s like having different engines for low- and high-rpm performance,” said Sutter. “The camshaft profile and valve timing is completely different at low and high speeds, for excellent performance across the board.”

      The camshaft design alters the lift of the intake and exhaust valves. As the engine load changes, electromagnetic actuators allow a movable shaft containing different cam lobes to shift imperceptibly between high-lift and low-lift profiles.

      Lift is the distance the valve travels from its seat when opened, and duration is the amount of time the valve remains open. Higher lift and longer duration allow more air to flow into the combustion chamber, so the system’s high-lift lobe profile enhances performance at higher rpm, while the low-lift profile optimizes efficiency at low- and mid-range speeds. Dual-Volute Turbocharger Builds Torque

      The 2.7L Turbo engine employs an advanced dual-volute turbocharger that elevates the performance and efficiency advantages of a conventional turbo, with quicker response and enhanced low-rpm torque production.

      Rather than a single spiral chamber (volute) feeding exhaust gas from the exhaust manifold to drive the turbine on the turbocharger, the dual volute design has a pair of separate chambers with two exhaust gas inlets and two nozzles to drive the turbine. The design allows the exhaust pulses of the engine to be leveraged for faster spool-up and subsequent boost production, particularly at low rpm, where the effect significantly enhances torque output and drivability.

      It works in unison with the engine’s integrated exhaust manifold/turbocharger housing, which splits the exhaust channels from the cylinder head so the exhaust flows through two separate channels in the turbo housing, based on the engine’s exhaust pulses. When complemented by the precision of the engine’s valvetrain, that separation leverages exhaust scavenging techniques to optimize gas flow, which decreases exhaust gas temperatures, improves turbine efficiency and reduces turbo lag.

      An electronically controlled wastegate and charge-air cooling system support the turbocharger and enhance its effectiveness. Compared to a conventional wastegate, the electronically controlled version offers more precise management of the engine’s boost pressure for smoother, more consistent performance.

      With the charge-air cooler, the pressurized, heated air generated by the turbocharger is pumped through a heat exchanger before it enters the engine. That lowers the air charge temperature by about 130 degrees F (74 C), packing the combustion chambers with cooler, denser air that enhances power production. The system achieves more than 80 percent cooling efficiency with less than 2 psi (12 kPa) flow restriction at peak power, contributing to the engine’s available torque production at low rpm. Additional Features

      Additional engine technologies supporting the engine’s performance and efficiency include:
      • Dual-volute turbocharger housing for improved throttle response and low-speed torque.
      • A variable-pressure oiling system with a continuously variable-displacement vane oil pump enhances efficiency by optimizing oil pressure as a function of engine speed and load. With it, the oil supply is matched to the engine requirements rather than the excessive supply of a conventional, fixed-displacement oil pump.
      • GM’s first application of Active Thermal Management, which helps the engine warm up faster and achieve its optimal engine temperature for performance and efficiency. The system uses a rotary valve system to distribute coolant through the engine in a targeted manner. It sends heat where it’s needed to warm up the engine to reduce friction and heat the cab, or cools when needed for high power operation. The result is improved engine performance in hot and cold ambient temperatures.
      • An electric water pump — a first for GM trucks — supports the Active Thermal Management system and further enhances the engine’s performance and efficiency by eliminating the parasitic drag that comes with a conventional, engine-driven water pump. It also enables continual cabin heating even when the engine is disabled by the stop/start feature.
      • Direct fuel injection is used to optimize efficiency and performance. With direct injection, a higher compression ratio (10.0:1) is possible because of a cooling effect as the injected fuel vaporizes in the combustion chamber, reducing the charge temperature and improving resistance to spark knock. Direct injection also enables gas scavenging from the combustion chamber to the turbo for fast response.
      • Dual overhead camshafts contribute to the 2.7L Turbo’s smoothness and high output, with dual independent continuously variable valve timing working with the valvetrain to deliver optimal performance and efficiency. The dual independent system, which allows the intake and exhaust valves to be phased at different rates, promotes linear delivery of torque with near-peak levels over a broad rpm range, and high specific output (horsepower per liter of displacement) without sacrificing overall engine response or driveability.
      • An integrated exhaust manifold that is part of the cylinder head assembly and recovers exhaust heat for faster engine and transmission warmup, with quicker turbo response.
      • Oil jets located in the block are employed for performance and temperature control. They target the underside of the pistons and the surrounding cylinder walls with an extra layer of cooling, friction-reducing oil. The jets reduce piston temperature, allowing the engine to produce more power and enhance long-term durability.
      • Stop/start technology that automatically stops the engine in stop-and-go traffic for fuel efficiency, enhancing fuel economy in city driving. The driver-selectable system shuts off the engine at stoplights and certain other stop-and-go situations, saving fuel. The engine automatically restarts when the driver takes their foot off the brake.
      Last edited by John; 05-14-2019, 09:38 AM.
      Excited owners of a 2015 Z06. Lifetime, annual contributors, and 20 year members of NCM. Our 2020 ME C8 Corvette is next.


      • #18
        Originally posted by John View Post
        Also HP will be found in incorporating most of the engine efficiencies GM pioneered in its 2.7L new motor (first identified and shared thanks to JB). Not all of them of course (not turbo in the LT2 as just one example, but probably more than a few of the following:[/LIST]
        This engine sounds like one of the two cylinder banks from the Blackwing as a stand alone 4-I


        • #19
          During the life of the C8, an opportunity to stimulate sales is to be found in unique powertrain offerings with aero combinations. In the past it has been base pushrod, and supercharged pushrods.

          Porsche offers a naturally aspirated that really spins high, for example.

          The C8 has both pushrod and DOHC. May offer varieties of each. But it a cost thing and the testing required. The supercharged stuff is a known. So. We will see.