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Old 09-25-2009, 11:55 AM   #2
Mr. Wyndham
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High-Flow Roto-Cast Cylinder Heads
The 6.2L Supercharged LSA cylinder heads are similar to those used on the naturally-aspirated 6.2L LS3 Corvette V-8, with enhancements for supercharged induction and maximum durability.

The LSA heads feature a unique "wing'' cast into each intake port to promote a swirling motion that blends the pressurized air-fuel charge. The heads are also cast from a premium A356-T6 alloy, which better manages the heat generated in a supercharged engine. A356-T6 pays particular dividends in the thin bridge area between the intake and exhaust valves, where effective heat dissipation is crucial to both performance and long-term durability. Finally, the LSA heads are rotacast. This process rotates the head mold as the molten alloy cools and essentially eliminates porosity, or microscopic pockets of air trapped in the casting. Rotacasting delivers a stronger part that helps maintain performance and structural integrity over the life of the engine.(The heads are nearly identical between the LS9 and LSA)

Low-friction hydraulic roller lifters actuate the LSA's valves, with unique offset rocker arms for the intake valves. On the inlet rocker, the valve tip is offset six millimeters from the pushrod. This configuration allowed GM engineers to locate the intake port for a more direct air-fuel flow into the combustion chamber. (This feature is also shared between the LSA and LS9)

Valves are among the most heat-stressed parts in an engine, and their wear resistance is crucial to long-term durability. Those in the LSA are manufactured from a high-chromium steel alloy called SilChrome 1 (The only difference between the LSA's exhaust valves, and the LS9s is that the LS9's are filled with sodium for the extra heat protection -- the LS9s intake valves are made of titanium.), with thicker heads than most other Gen IV V-8s. They promote heat transfer away from the valve face and valve guide to the cooler end of the stem, where it more readily dissipates. This maintains a lower, more uniform valve temperature, reducing wear on the valve guide for better alignment and a consistent seal between the valve seat and valve face over the life of the engine. The intake valves measure 55 mm in diameter and the exhaust valves, 44 mm.

Given the LSA's pressurized induction, GM engineers focused special attention on sealing. Head gaskets are extra-robust, four-layer stainless steel, ensuring gasket sealing under the high combustions pressures generated by the LSA.(These gaskets are also used on the LS9, the LS9, though uses mildly stronger head bolts, as well to deal with the extra 70-some hp)

Center-Feed Fuel System
The 6.2L LSA's fuel system was developed to deliver adequate fuel volume precisely, consistently and quietly.

To ensure appropriate fueling in all conditions, from casual cruising to race track-type wide-open throttle, GM has equipped the LSA with a dual- pressure fuel system. The system delivers 250 kPa (about 36 psi) at idle or low speeds. Yet the electronic throttle management system can almost instantaneously increase fuel pressure to 450 kPa (65 psi) for sustained high-speed operation or wide-open throttle. The dual-pressure system reacts according to throttle application, and presents several advantages. It limits the energy used by the fuel pump at low speeds, for maximum efficiency, and it reduces operational noise. It also ensures adequate fuel delivery when the LSA demands its maximum flow rate of 50 grams per second.

The LSA also employs a new center-feed fuel rail that delivers gasoline to the center of the injector rail on each bank. The delivery point is roughly equidistant to each of the injectors, which have a maximum flow rate of 6.52 grams per second at 400 kPa. Fuel pressure variation among the injectors is reduced, and so is noise. The rapid ticking sound often generated by fuel injectors is alleviated.

An 87-mm, single-bore throttle body draws air into the engine. The electronic throttle maps have been optimized for excellent response and modulation in a multitude of driving scenarios.

Direct-Mount Ignition Coils
The 6.2L LSA's coil-on-plug ignition features advanced coils developed for the 7.0L LS7 V-8 in the Corvette Z06. These coils are smaller and lighter than those used on previous small-block V-8s. An individual coil for each spark plug delivers maximum voltage and consistent spark density, with no variation between cylinders.

The LSA ignition system is unique nonetheless, as the coils mount directly on LSA-specific rocker covers. Those on the naturally aspirated 6.2L LS3 and LS7 are joined by a bracket. The individual LSA coils provide a cleaner look and a shorter lead between the coil and the iridium-tip, center-electrode spark plug.

E67 Control Module
An advanced controller manages the multitude of operations that occur within the 6.2L Supercharged LSA V-8 every split second. The E67 is the high-line controller in GM's family of three engine control modules (ECM), which was developed to direct nearly all the engines in GM's line-up. It features 32-bit processing, compared to conventional 16-bit processing, with 32 megabytes of flash memory, 128 kilobytes of RAM and a high-speed CAN bus. The E67 synchronizes more than 100 functions, from spark timing to cruise control operation to traction control calculations, and it has more computing power than the typical desktop PC 20 years ago. It works more than 50 times faster than the first computers used on internal combustion engines in the late 1970s, which managed five or six functions.

The family strategy behind GM's ECMs allows engineers to apply standard manufacturing and service procedures to all powertrains, and quickly upgrade certain engine technologies while leaving others alone. It creates a solid, flexible, efficient engine-control foundation, freeing engineers to focus on innovations like the LSA’s advanced supercharging technology, and to get them to market more quickly. GM creates all the software for the three ECMs, which share a common language and hardware interface that's tailored to each vehicle.

The E67 also applies a rate-based monitoring protocol sometimes known as run-at-rate diagnostics. Rate-based diagnostics improve the robustness of the Onboard Diagnostics System (OBD II) and ensure optimal performance of emissions control systems. The software increases the frequency at which the ECM checks various systems, and particularly emissions-control systems such as the catalytic converter and oxygen sensors. Rate-based diagnostics more reliably monitor real-word operation of these systems, and allow regulatory agencies to more easily measure and certify emissions compliance. With the E67, the CTS-V's environmental performance matches its race-track potential.

Upgraded Oiling System
To ensure peak, low-friction efficiency, and to promote durability during extended high-rpm operation, the 6.2L Supercharged LSA has a more powerful oil pump than the naturally aspirated 6.2L LS3. Pump capacity increases to 33.8 gallons per minute. The LSA's six-quart oil pan is fitted with a liquid-to-air oil cooler. This is, ironically, a lower oil-capacity than the LS3 and L99s found in the Camaro.

Revised Accessory Drive
The 6.2L LSA's accessory drive system accommodates the supercharger with a third track on the crankshaft pulley. The supercharger is operated by its own belt, which is wider than a conventional belt (eight ribs) to turn the rotors without slip. The other drive belts are conventional five-rib widths, with one operating the air conditioning compressor and another operating the water pump, power steering pump and alternator.

Cast-Iron Exhaust Manifolds with Close-Coupled Catalysts
The 6.2L LSA exhaust manifolds are fabricated from a premium high-silicon, high-moly iron alloy. The material delivers excellent heat management properties, and the design ensures the high flow volume required of an engine with the LSA's capability. Moreover, cast iron radiates less noise than other materials such as stainless steel, making it the preferred choice in a luxury sedan.

Immediately downstream, the exhaust manifolds are fitted with a pair of close-coupled catalytic converters that heat quickly, achieving light-off temperature and closed-loop operations in seconds. The primary catalysts are further downstream under the vehicle floor.

Acoustic Engine Cover
The LSA is trimmed with special engine cover surrounding the intercooler and supercharger case, which is visible under the CTS-V's hood. The cover has "SUPERCHARGED LSA" script on each side, with the V-spec logo and classic Cadillac laurel emblem front-and-center.

The engine cover helps isolate high-frequency sounds emanating from the engine, and it's attached with ball-stud mountings that more effectively limit vibration transfer than conventional twist-in fasteners. It's also lined with dense acoustic foam.

The 6.2L Supercharged Gen IV LSA V-8's credentials speak for themselves. It's the most powerful production engine in Cadillac's storied history, with 556 horsepower, high-rev capability and higher specific torque than any of its competitors. It makes the Cadillac CTS-V one of the world's fastest, most capable sedans.

A Cadillac, of course, demands smooth, refined operation, and the LSA delivers here, too. Measured by interior noise levels at cruising speed and wide-open throttle, the 2009 CTS-V is substantially quieter than its highly successful predecessor, with cabin noise measurements that meet or beat Europe' best ultra-performance luxury sedans.

Measured by cost-to-performance ratio, the LSA might also be considered a relative bargain. The elegant simplicity in the small-block V-8's DNA means cost-effective development and production, and that translates to value, for customers and the corporation. Yet an emphasis on value overlooks one significant point. The LSA is one of the best high-performance sedan V-8s in the world, regardless of price.

GM's 90-degree small-block car engines remain unique in the automotive world: high-tech, aluminum-intensive, ultra-high-performance cam-in-block V-8s. The LSA adds a supercharger to the mix, and pushes the combination of impressive low end torque and free-breathing, high-rpm horsepower to a new level.

The starting point for the LSA was the first engine built for the sixth-generation Corvette-the Gen IV 6.0L LS2 V-8. The LS2, in turn, had built on two milestone engines: the LS1 and LS6 V-8s developed for the C5 Corvette. Those Gen III engines had introduced a host of leading-edge technologies to the grand tradition of GM's small block, starting with all-aluminum construction, a thermoplastic intake manifold and drive-by-wire electronic throttle. With them the engineers and analysts who claimed cam-in-block engines could not meet the performance demands of a new millennium--or increasingly stringent emissions standards-were proven patently wrong.

Within this evolution, and a data base only tradition can provide, rests the cornerstone of small-block value. The performance in the LSA comes with 76 percent carryover parts from other small-block V-8s, while 25 percent of the new parts are common to the supercharged LS9 V-8 for the 2009 Chevrolet Corvette ZR1. The value is enhanced by GM's advanced application of math-based computer tools. GM engineers created 370 different power simulations to optimize the LS9 and LSA. One simulation takes 24 hours, while one engine build takes nine weeks. Both the LS9 and LSA V-8s met power requirements out of the box. It's value without compromise, in performance, emissions or customer satisfaction.

Regarding quality and durability. The 6.2L Supercharged LSA has been validated beyond 100,000 miles and accumulated more the 6,400 hours of dynamometer testing. It has run over 270 consecutive hours at wide-open throttle without a failure. (The LS9 has only accomplished 100 hours of this sort of testing!!!) It's been road tested in the world's extreme climates and track-tested under racing g loads on some the world's most demanding circuits. It has completed actual and simulated 24-hour track tests.

And if its output and high-speed potential seem to suggest otherwise, the LSA nonetheless requires minimal maintenance. Its advanced iridium-core spark plugs and Dexcool coolant are validated to 100,000 miles of operation, with the same level of performance at 90,000 miles as they deliver at 10,000. The LSA also features GM's advanced Oil Life System. This technology measures stress on the engine and calculates oil life based on real-world use--whether it's profiling or extended, no-limit autobahn blasting--rather than a predetermined mileage interval. The Oil Life System eliminates unnecessary oil changes in vehicles that are driven in light-duty conditions.Each engine/vehicle combo gets it's own tailored Oil Life Monitor algorithm, so the LSA's monitor will provide the same level of accuracy as a 149hp Cobalt.

For all the improvements and advanced technologies built into the 6.2L Supercharged LSA V-8, the bottom line still counts most. This is an ultra-high performance engine, with capabilities suited to one of the best performing sedans in the world.
"Keep the faith." - Fbodfather
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