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When You Want 16 Cylinders...

A thousand horsepower concept.

Courtesy GM

Click on pics to view larger images


The new GM XV16 concept engine, unveiled in the Cadillac Sixteen show car, features a huge 13.6-litre V16 engine. While way over the top it also exhibits some of the engineering features that will be released by GM in the next few years. Significantly, it uses only two valves per cylinder and is a pushrod design.

The XV16

GM's XV16 concept engine is a naturally aspirated, all-aluminium 13.6-litre V-16 that generates more than 1000 horsepower (746 kW) and 1000 lbs.-ft. (1356 Nm) of torque. Building on GM Powertrain's small-block V-8 engine architecture, the V-16 features many of GM's advanced next-generation valvetrain and fuel-saving technologies including 3-step Displacement on Demand.

"The V16 affirms Cadillac's leadership ambition with a powerful statement," said Thomas G. Stephens, GM group vice president of GM Powertrain. "This elegant engine, thoroughly modern in every respect, is a fitting tribute to the automotive industry's first 16-cylinder engine that Cadillac introduced more than 70 years ago."

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The advanced V16 concept engine embodies many of GM's innovations in overhead-valve engine architectures.

GM Powertrain had a clear, challenging list of objectives to meet with the new V16 concept: outstanding quality, reliability and durability, plus turbine-like levels of noise, vibration and harshness. The XV16 needed to be as fuel-efficient as comparable V10 and V12 competitive engines. It had to have class-leading specific output and lower engine weight than current big-block V8s. With all of these requirements, it also had to run on regular unleaded fuel.

All of the objectives were met or exceeded. Even more impressive was the fact that the engineering team working on this project designed, built and demonstrated a working engine in less than eight months.

The Design

"The XV16 is an uncomplicated, technically elegant design that sets new levels for efficient, silky-smooth, ultra-quiet operation," said Stephens. "Its power and torque levels are also beyond any other engine of which we know."

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High fuel efficiency and low emissions were a top priority in the design and development of the XV16. The XV16 has cylinder head ports and a combustion chamber that have been analytically optimized to provide smooth, quiet and complete combustion. The advanced combustion system reduces emissions and improves fuel economy simultaneously. Sequential multipoint fuel injection is utilized in conjunction with precisely targeted injectors to minimize engine-out emissions. Spark is delivered by high-energy ignition coils for a clean, fast burn. The engine-management system monitors mass airflow to accurately control fuel and spark delivery under all operating conditions.

The concept engine was also designed to be a very space- and weight-efficient engine. The XV16 weighs 695 pounds, 64 pounds less than the Vortec 8100 V-8 featured in the Chevrolet Avalanche, Silverado and Suburban, and GMC Sierra and Yukon XL. The engine's front profile is significantly smaller than that of a dual overhead cam V6/V8/V12 design. And the XV16, with twice the number of cylinders, has fewer parts than any DOHC V-8 engine in the industry, thus -according to GM - underscoring another major benefit of overhead-valve designs.

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GM Powertrain engineers benchmarked the port geometry of racing engines in designing the XV16. The result is a two-valves-per-cylinder engine with airflow characteristics that rival four-valves-per-cylinder engines.

Computer-aided analysis and simulation were used extensively in the design of some of the major components, such as the block, crankshaft, cylinder head, valvetrain, cooling and lubrication system.

Key Features

The valvetrain is designed to expand the performance envelope of the conventional pushrod, two-valve engine while maintaining the inherent advantages in packaging efficiency and mass.

The XV16's valves are titanium alloy, an extremely lightweight material. The engine also employs titanium alloy valve springs, which are 40 percent lighter than comparable steel designs. The titanium helps increase the springs' natural frequency by 28 percent to allow for higher engine speeds.

Because of its overhead-valve architecture and roots in GM's next-generation small-block V8, the XV16 is a perfect candidate to feature GM's Displacement on Demand (DoD) fuel-saving technology. This technology enables the engine to run seamlessly on eight or even four cylinders during typical driving conditions to maximize fuel savings.

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The XV16 engine is started on all cylinders to provide fast, clean starts in all conditions. Once running, the powertrain control module activates DoD based on speed and load conditions using inputs from a number of sensors. Under light load conditions, the control module automatically closes both intake and exhaust valves on selected cylinders. The valves are reopened to provide the number of cylinders needed for exhilarating acceleration or for hauling heavy loads.

DoD leverages the existing oil pump to provide hydraulic pressure to activate the system. The mechanical actuators are special hydraulic lifters, each with a spring-loaded locking pin that deactivates the cylinders.

These special lifters are designed so that one section can collapse, or expand, into the other section. The two sections can be either coupled or uncoupled to each other through the locking pin. When DoD is initiated, hydraulic pressure is used to dislodge the locking pin and collapse the lifter, thus closing the valve. In reactivation mode, the removal of hydraulic pressure causes the locking pin to return to its latched position, restoring the lifter's normal function.

When in V8 or V4 mode, a balanced combination of cylinders would be used to maintain smooth engine operation. Cylinder deactivation-reactivation operation is accomplished in a fraction of a second, making the transition seamless and transparent to the driver.

Based on GM's fuel-economy analysis, on a drive from Detroit to California, the XV16 would operate in eight-cylinder mode 65 percent of the time, four-cylinder mode 30 percent of the time, and in 16-cylinder mode only 5 percent of the time.

With the XV16's 3-step DoD system, you get the added benefit of having greater performance with all 16 cylinders in certain wide-open throttle situations such as safely passing on a two-lane road, climbing a very steep grade, or simply having fun.

As with Displacement on Demand, variable cam phasing further enhances the XV16's fuel economy, emissions and power output. An electro-hydraulically actuated position controller varies the camshaft timing relative to the crankshaft. The use of cam phasing also eliminates the need for an external exhaust gas recirculation (EGR) system to control engine-out NOx emission.

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The cam phaser enables increased torque at low speeds by positioning the camshaft with an earlier inlet valve closing to trap more fresh combustion mixture. It also can be used to modify the "effective" compression ratio, allowing for increases in initial compression ratio for improved fuel economy and performance. A phaser authority of greater than 40 degrees allows for overall optimization of power, fuel economy and emissions.

This powerful engine also generates a lot of heat under high load conditions. Piston squirters allow the engine to run at higher engine speeds and loads, and keep the pistons cool. The squirters target oil at the underside of the pistons to help remove heat. Oil is also directed at the cylinder wall to help provide a quieter start-up.

The GM XV16 also uses a dry-sump scavenge pump system integrated with the main oil pressure pump. The dry-sump helps reduce overall height for improved packaging while making the vehicle capable of more aggressive cornering. The system has eight individual scavenge pumps to evacuate oil from the sump for improved performance and fuel efficiency.

"The technologies featured in the XV16 engine - all-aluminium construction, DoD, cam phasing, advanced port and combustion chamber design, piston cooling and advanced materials - are all indicators of where we are headed with our next-generation overhead valve engines," said Stephens.

GM XV16 Specifications

Configuration:

13.6L V16

Installation:

longitudinal RWD

Displacement:

13,600cc

Valvetrain:

OHV 2 valves-per-cylinder

Bore x Stroke:

105 mm x 98 mm

Horsepower:

1000 (746 kW) @ 6000 rpm

Torque:

1000 lbs.-ft. (1356 Nm) @ 4300 rpm

Compression ratio:

10.6:1

Firing order:

1-12-8-11-7-14-5-16-4-15-3-10-6-9-2-13

Fuel system:

sequential multipoint fuel injection

Recommended fuel:

unleaded regular


The Northstar XV12 Concept
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In addition to pursuing pushrod engine designs, GM has also developed large capacity DOHC concept engines. The Northstar XV12, first shown in 2001 in the Cadillac Cien concept car, is a 60-degree, all-aluminium dual overhead cam (DOHC) four-valve engine. It displaces 7.5 litres and produces 750 horsepower (560 kW) and 450 lb-ft of torque (610 Nm).

"The Northstar XV12 provides a realistic look at what could power an assault on the high-end, premium automotive segment," said Fritz Indra, GM Powertrain executive director of advanced engineering. "At the same time it showcases a wealth of new technologies under development at GM Powertrain, many of which will eventually find their way into GM engines of all shapes and sizes."

Some of the high-tech features included in Northstar XV12's capabilities:

  • Displacement on Demand

The cylinder shutdown is enabled through valve deactivation, which is performed by a compact switchable tappet. Cylinder de-activation occurs on the right-hand bank only, which allows the engine to run as a perfectly balanced inline 6-cylinder. The system deactivation and reactivation has a quick response time and the oil system and solenoid layout allows valve switching capability at up to 6000 rpm. GM has announced that it will implement Displacement on Demand in its trucks and SUVs beginning in 2004.

  • Direct Injection Gasoline

Using a direct-injection gasoline combustion system provides an increase in engine power and also improves fuel economy and cold-start hydrocarbon emissions. The multiple injection set-up also improves emissions and performance through faster catalyst light-off. The single fluid high-pressure fuel injector is centrally located in the combustion chamber, and sprays the fuel vertically down to the piston.

  • Variable Cam Phasing

The use of variable cam phasing helps the Northstar XV12 achieve 90 percent of its maximum torque at 1500 rpm, improves combustion stability at idle, improves fuel economy by reducing pumping losses and can be used to speed up catalyst light-off to significantly improve emissions. It provides internal exhaust gas recirculation (EGR), which is more reliable and cost-effective than an external EGR set-up.

  • Variable Intake Manifold

The Northstar XV12's three-stage variable induction system with tuned primary and secondary pipes results in a flat torque curve. It's a simple, compact and reliable design. Electric variable intake valve actuators enable rapid changes in manifold geometry over conventional pneumatic actuators.

  • Rear Chain Timing Drive

Many of the engine's accessories are run off the rear chain timing drive, creating opportunities for better packaging by eliminating the need for a front engine accessory drive and reducing the engine's overall length, as well as the height of its front end. The robust yet quiet-running chain drives the engine's camshafts, high-pressure fuel pump, oil pump, and hydraulic power-assist steering pump, and also has the potential to drive the water pump and air conditioning compressor.

  • 58,000km Oil Change Interval

The Northstar XV12 is designed for 58,000-kilometre intervals between oil changes. This is achieved through a combination of improved oil sensors and monitors, reduced oil consumption, oil cooling and a larger oil sump capacity.

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