Corvette C5-R LS1 Engine: Two-Valve Technology for the 21st Century
Corvette C5-R LS1 Engine: Two-Valve Technology for the 21st Century
Source: GM Media
GM's family of LS1 overhead-valve V-8 engines can trace its roots to the fabled Chevrolet small-block V-8, yet the LS1 is much more than an offshoot from the small-block family tree. The LS1 continues the small-block's longstanding virtues of compact size, simplicity, reliability and high specific output.
When the all-new production LS1 debuted in the fifth-generation Corvette in 1997, it provided a potential foundation for the C5-R engine program. But GM Racing engineers faced a dilemma: Just how do you update the most successful engine in motorsports history?
Their answer: Build an even better small-block.
"Before the introduction of the LS1, almost every V-8 engine used for racing dated back to designs that originated in the mid-'50s," said Doug Duchardt, director of GM Racing. "The GM small-block V-8 that was the cornerstone of America's racing industry for nearly 50 years is being replaced by derivatives of the LS1, which has the highest specific output of any production V-8 engine GM has ever built.
"The LS1 is truly the high-performance small-block V-8 of the future," Duchardt noted.
Think of the race-prepared engines that power Corvette Racing's C5-R coupes as small-blocks on steroids - bigger and more powerful than their production counterpart, but still small-block V-8s at heart. In fact, the heavy-duty blocks and cylinder heads designed by GM Racing engineers for the Corvette factory racing team are based on the design of the production parts - and are available to independent racers through GM Performance Parts.
While the production LS1 engine displaces 5.7 liters (346 cubic inches), the racing version is a brawny 7.0 liters - a displacement that stirs memories of the 427-cubic-inch big-blocks of the '60s. According to a familiar hot rodding adage, there's no replacement for displacement - but in the case of the C5-R engines, the cubic inches are complemented by advanced technology.
The ALMS rules mandate the use of air restrictors to equalize the performance potential of the wide variety of cars that compete in the series. The size of the restrictor is determined by the vehicle's weight, engine displacement, induction system (naturally aspirated or turbocharged), and other factors. The C5-R Corvette, for example, is required to breathe through two 31.8 mm restrictors. These orifices are about the size of a 50-cent piece.
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Much like the carburetor restrictor plates used by NASCAR on superspeedways, the ALMS air restrictors limit airflow through the engine, thereby controlling the horsepower produced. Moreover, ALMS officials can change the size of the restrictor orifice to maintain a level playing field.
"The 7.0-liter engine combination allows us to run relatively low rpm to maximize fuel economy and reliability while producing extremely high torque numbers that make the cars very 'driver-friendly' on a road course," explained GM Racing engineer John Rice.
The key components of the C5-R racing engine are a heavy-duty, siamesed-bore cylinder block and CNC-machined competition cylinder heads. Although these are purpose-built parts, they have close ties to their production counterparts.
"We designed the competition engine using as many production parts and processes as possible," said GM Racing engine specialist Ron Sperry. "In order to reach our performance targets, we had to modify the block design. GM Powertrain engineers had some prototype block configurations they were studying for future products, and they made some of these available to us for the C5-R engine development program."
The production and competition LS1 aluminum blocks share the same deep-skirt design, with oil pan rails that extend below the crankshaft centerline to improve stiffness and rigidity. Each main bearing cap is secured by six fasteners - four vertical fasteners that attach to the main bearing bulkheads and two additional cross-bolts that anchor the caps to the sides of the block. The cross-bolted main caps and deep-skirted crankcase minimize block distortion and bending under high loads. On the street, this stiff block structure reduces noise and vibration.
Externally the production and racing blocks are virtually identical, with similar dimensions and mounting bosses. The chief internal difference between the production and racing blocks is the cylinder bore diameter. The production LS1's dry cast-iron cylinder liners are fully water-jacketed with coolant passages between adjacent cylinders to enhance cooling. The racing version has siamesed cylinders without water passages between adjacent bores. This modification allows engine builders to increase the bore diameter from the production 3.90-inch dimension up to a maximum of 4.160-inch diameter for racing.
The LS1's wide, stiff crankcase accommodates a long-stroke crankshaft without clearance problems. The production cast nodular iron crank has a 3.60-inch stroke; the racing engines use 3.985-inch stroke crankshafts machined from steel billets.
The GM Racing aluminum cylinder heads are designed to meet the airflow requirements of the racing engine's increased displacement and higher operating speed. Like the motorsports block, the competition cylinder heads have close ties to the assembly line.
"The racing cylinder heads were generated from the same 3D data files used for the stock heads," Sperry said. "The valve angle was revised from 15 to 11 degrees and the combustion chambers were redesigned to match the racing engine's bigger bores, but externally they look much like the production heads."
Both the street and competition LS1 engines have evenly spaced, symmetrical intake and exhaust ports. The LS1's intake ports are tall and narrow, a design that produces high mixture velocity for efficient combustion and complements the injector position used with the production sequential electronic fuel injection (SFI) system. The racing manifold substitutes eight individual throttle butterflies for the production engine's single throttle body, but it retains the stock injector location.
"Few people realize the long-term effect that the LS1 engine is going to have on the performance industry," said Duchardt. "It was Zora Arkus-Duntov's vision in 1953 that Corvette should lead the way with race-ready parts and designs. I think he would be proud of what has been achieved with the LS1."
Sidebar 1: Dial Z06 for Performance
Powered by a 405-horsepower LS6 small-block engine, the 2004 Corvette Z06 hardtop is the highest performing member of the Corvette family. The Z06 designation pays homage to the concept of an ultimate performance option advanced by Corvette Chief Engineer Zora Arkus-Duntov in 1963 with the introduction of the stunning split-window Sting Ray coupe.
The original RPO (Regular Production Option) Z06 package included a fuel-injected 327-cubic-inch small-block V-8, a four-speed manual transmission, and heavy-duty suspension upgrades such as a limited-slip differential and finned brake drums - in short, everything a Corvette owner needed for a day at the races. A total of 199 ZO6-equipped coupes were produced.
Today's Z06 is the quickest, best handling production Corvette ever, with fuel economy, comfort and sophistication that would have seemed impossible in 1963. The Z06 is powered by a 5.7-liter (346 ci) LS6 engine that produces 71 horsepower per liter, the highest output of any GM small-block V-8. To reach this lofty power level, the LS6 uses a low-restriction Mass Air Flow (MAF) sensor, lightweight hollow-stem valves, a high-lift camshaft, a free-breathing exhaust system and other enhancements.
The LS6 also honors Corvette's performance heritage by reviving the designation that identified the brawny 454-cubic-inch/450-horsepower big-block V-8 in 1970.
"There is more than one way you can design an engine to achieve this power level," said Sam Winegarden, GM Powertrain executive director, engine engineering. "Conventional wisdom says that you need a four-valve, overhead cam arrangement, and that is just not the case. The LS6 shows that the pushrod small-block has a bright future, and there's more where that came from."