LS/LT Encyclopedia: Modern GM Small-Block V-8s, Part 1

Welcome to a brief series that charts the evolution and features of the modern GM small-block. We begin with a quick backstory and then hop into the details of the most ubiquitous V-8 engine family of the 21st century. Stay tuned for parts two and three. —Ed

Preamble: The Road to LS

In 1955, Chevrolet chief engineer Ed Cole introduced the world to the small-block Chevy V-8. His revolutionary design was the perfect recipe to satisfy a domestic market ravenous for attainable speed. The small-block “mouse motor” was lighter and more compact than any of GM’s previous work in the field of bent eights, not to mention that of its unsuspecting contemporaries from across town or the six-bangers it replaced in Bow-Tie showrooms. This condensed V-8 cemented its status with big power and even bigger potential in the aftermarket.

For nearly two decades, The General continued to perfect Cole’s blueprint, extracting more and more power through the introduction of fuel injection and higher compression ratios. Weight was cut through the use of new materials and manufacturing processes. Even after the day the horsepower died, Cole’s masterpiece would soldier on into the malaise era of the late ‘70s and early ‘80s as a faintly shining beacon, reminding gearheads of the good days while offering as much oomph as it could legally get away with.

Father(s) of the LS: The DOHC LT5 and the Short-lived Gen II Stepping Stone

By the mid-’80s, General Motors was ready to spark an American performance comeback by minting a powerplant that could live up to the acclaimed handling of its hot new C4 Corvette. Coincidentally, GM had a controlling interest in Lotus at the time, so, naturally, the famed sports car maker and seven-time F1 Constructor’s champion was tapped to take the lead on the “King of the Hill” project. The LT5 V-8 that materialized from this partnership shared its 5.7-liter displacement and trademark 4.4-inch bore spacing but not much else with its lesser siblings. It brought dual-overhead cams to America’s Sports Car for the first time. Its four valves per cylinder were joined by 16 fuel injectors and a bottom end built from an aluminum block with a forged steel crank and connecting rods that netted an 11.0:1 compression ratio. Its state-of-the-art construction brought a third partner, Mercury Marine, into the fold to handle assembly. From the time the C4 ZR-1 that housed this masterclass in modern combustion hit the market in 1990 through 1992, the LT5 made 375 raucous horsepower vs. the 245 of the L98 in the base ‘Vette and, for context, the 225 of the “5.0” in the most powerful Mustang on the market; it was a monster!

The ZR-1’s uncanny ability to sustain 175 MPH immediately became the stuff of legend, and as Lingenfelter would later prove, the LT5 still had a lot of room to grow. However, the high expense of its production and the public’s waning interest in buying ZR-1s forced GM into a difficult crossroads with far-reaching implications. With an improved 405-horse LT5 set to bow in 1993 and the possibility of a 475 or even 500 HP variant within reach, Option A involved staying the course and further developing the 32-valve motor that already had significant time, money, and effort sunk into it. Option B? Pulling the plug with a drastic cost-cutting righthand turn, taking everything learned from the pricey ZR-1 detour and applying it to its birthright by vastly improving the timeless pushrod V-8.

The offramp was taken, the band-aid was ripped off, and the first Gen-II small-block was born. It was dubbed LT1 as an homage to the Mighty Mouse’s 1970 highwater mark. The new LT1 used a new block, intake manifold, and cylinder heads along with a “reverse cooling” system, but the basic design, including engine mounts, bolt patterns, bore spacing, and the 5.7L displacement of its direct predecessors, carried over for maximum parts sharing between generations.

This revamped LT1 hit base Corvette engine bays in 1992 with an even 300 ponies and 330 lb-ft of twist, delivering once again on the premise of affordable performance by offering 90 percent of its high-tech big bro’s performance at a 50 percent discount and almost instantly pushing the mighty ZR-1 into the background of public consciousness.

With GM’s final obligation to the LT5 complete and one model year remaining before the changeover to the long-awaited C5 Corvette, the stopgap Gen-II small-block earned itself a swansong upgrade for 1996. Meant as the mechanical highlight for the one-year homage to the fabled Grand Sport racers of the ‘60s—but featured in every manual transmission 1996 ‘Vette—the LT1 was worked over with a lightweight valvetrain and strengthened crank, resulting in a 30-horse bump and a unique “LT4” designation to take the Chevy small-block’s fleeting but significant second iteration into the sunset in style.

LS Rises: The Complete Guide to Gen-III Performance Small-Blocks

Engine: LS1

Displacement: 5.7L

Max Power/Torque: 350/365

Model Years: 1997-2004

Domestic Applications: C5 Corvette, Fourth-Gen Camaro/Firebird (1998-2002), 2004 Pontiac GTO

The Gen-III “LS” small-block made its debut in 1997 in where else but under the long, low (a characteristic feature permitted by GM’s re-commitment to pushrods earlier in the decade!), sculpted hood of the C5 Corvette. Its first representative, aptly dubbed “LS1,” still displaced 5.7 liters, but other than the familiar displacement, its characteristic 4.40-inch bore spacing, and its rod bearings, it represented a clean-sheet effort with flexibility at the core of its mission. As opposed to the LT1’s 4.00-inch cylinder bores and 3.48-inch stroke, the LS1 reached 5.7 liters through a 3.899 x 3.622 bore and stroke. From the word “go,” the third-gen small block was intended for use in cars and trucks, could be manufactured in either aluminum (cars—our focus, here) or cast iron (trucks), and able to take on multiple displacements. It quickly earned a reputation for durability, remarkable power production, and surprising efficiency while remaining easy and affordable for GM to manufacture and for dealers, tuners, and individuals to service, upgrade, and, of course, swap.

Engine: LS6

Displacement: 5.7L

Max Power/Torque: 405/400

Model Years: 2001-2005

Domestic Applications: C5 Corvette Z06, 2004-2005 Cadillac CTS-V

The hi-po version of the LS1 arrived along with the first modern Corvette Z06 in 2001. It also received nomenclature from the golden age of American muscle, earning the LS6 classification last used on 454 big-block Chevelles and Corvettes of the early ‘70s. The LS6 soldiered on at 5.7L but was fortified with improved main web strength, a higher-lift cam, greater compression (10.5:1), a revised oiling system, and more, including the first mass-market use of a titanium exhaust system following the lead of the McLaren F1. It debuted with 385 horses but proved GM’s bet on pushrods wise by equaling the LT5’s 405-horse output for a fraction of the cost in 2002. The LS6’s unique intake manifolds were also used on all 2001 and later LS1s, gifting the Corvette LS1 a five-pony boost from 345 to its final 350-horse form. When Cadillac was reborn in the sporting image of BMW a couple of years later, the first member of its M-fighting V-Series brought the strongest powerplant available—an LS6 with a five-HP Corvette tax imposed—together with the new-for-2004 Art and Science CTS sedan.