When GM relaxed its longstanding rule forbidding engines larger than 400 cubic inches to be installed in midsize cars, it set off a muscle frenzy across the company's divisions. Oldsmobile put the huge 455-cubic-inch into its 442, and Chevy installed a unique 454-cubic-inch V-8, the LS6, into its Chevelle SS.
A conservative estimate of the LS6's power puts it at 450 hp and 500 lb-ft of torque. But thanks to its high 11.25:1 compression ratio and giant Holley 780 CFM carb, the LS6's real output in the Chevelle SS was closer to 500 hp, many experts claim. Our pals at Car and Driver tested one in 1970 and found it hit 60 mph in just 5.4 seconds, running through the quarter-mile in 13.8 seconds. And that was with the skinny low-grip tires of the day; that same car with modern rubber would be much quicker. The LS6 carries the highest factory horsepower rating of all muscle cars.
Little-Known Fact: The Chevrolet Corvette has always been Chevy's top performance car. And up until the LS6, GM wouldn't allow any other Chevy to carry a horsepower rating higher than that of the Corvette. But somehow that stance was relaxed for 1970—the highest horsepower engine you could get in a 1970 Corvette was a 390-hp LS5 454. An LS7 was planned with 465 hp, but it was never officially sold. So why no LS6? An LS6 Corvette was offered for 1971, but its potency slipped (at least officially) to 425 hp.