Chevrolet's family of big block V8s had its glory years towards the end of the 1960s muscle car explosion, with models as diverse as the Corvette, the Impala SS, and the Camaro all benefiting from large-displacement torque and high horsepower fury.
Of these engines, one of the rarest and most celebrated is the 454 LS6. Although other versions of the 454 would go on to pull workhorse duty across a long list of pickup trucks, vans, and commercial vehicles, the LS6 was restricted to a brief, shining moment in General Motors history that sadly arrived just as the high performance party was coming to a close in Detroit.
The Biggest Chevy Muscle Car Motor
When the 454 cubic inch engine appeared in the Chevrolet catalog in 1970, it was intended to rule the streets by building on the same Mark IV design architecture that had defined the 427 cubic in V8 that preceded it. The 454 maintained the 427's 4.25 inch bore, but it increased the stroke to 4 inches, and it was offered to the public in two distinct versions.
At the entry-level was the 360 hp LS5, which was found full-size models like as the Caprice as well as in SS-badged cars like the Chevelle, the Monte Carlo, and the El Camino when equipped with the SS454 package (RPO Z15/LS5). It was also featured in the Corvette (where power jumped to nearly 400 hp). At the top end was the 450 hp LS6, which could be included with the Chevelle and the El Camino SS 454 cars for a modest sum by way of the RPO Z15/LS6 ordering code.
What set the LS6 apart from its more modest sibling? Compression on the engine ran 11.25:1, and its cast iron, rectangular port heads featured a 2.19 inch intake opening and a 1.88 inch exhaust opening. It also featured a solid lifter camshaft versus the hydraulic lifters on the LS5, with a .520 inch lift (exhaust and intake) and 316 degree duration, and came with a low-rise aluminum intake, forged aluminum pistons, and a massive 800 cfm four-barrel Holley carburetor. As with the LS5, Chevrolet also offered a cowl induction hood package that fed outside air directly to the carb.
Torque was rated at a whopping 500 lb-ft, with rumors that the engine's output was seriously underrated by GM to keep insurance companies from cranking premiums through the roof.
As Potent As The Hemi
Right from the start the SS 454 LS6 package was a contender for king of the street. Going by contemporary test results, magazines like Car Craft and Super Stock Drag & Illustrated had LS6-powered Chevelles mowing down the quarter mile in just a tick or two over 13 seconds, which was quicker than similarly-sized Mopars like the Plymouth GTX and the Road Runner sporting 426 cubic inch Hemi motors.
Strangely, the Corvette was denied the LS6 engine until 1971, making do with the LS5 as its only big block option when the 454 was initially launched. When it did arrive it was down on power by 25 ponies, checking in at 425 hp after being victimized by a lower compression ratio linked to the EPA's burgeoning campaign against automotive emissions. It did, however, offer aluminum heads versus the iron heads found on other versions of the LS6 (a weight savings of over 50 lbs), and a few other goodies (including a more durable crankshaft and stronger connecting rods).
The Chevrolet Corvette was only equipped with the 454 LS6 for a single model year, and 1971 was also the last hurrah for every other Chevy model that had access to the monster motor. Starting in 1972 the LS5 took over until the middle of the decade when it disappeared completely from the passenger car portfolio, having been choked down to well under 300 horses and then made irrelevant by the shock of the energy crisis and fuel shortage that sounded a death knell for thirsty V8 engines in America.
Catching Up With History
Today the LS6 is a legend. Although Chevrolet has since offered crate motors featuring more power and torque, it's still a sought-after spec for collectors or clone builders who simply want the hottest big block Bowtie engine of the era powering their project.
Auction prices for original equipment LS6 cars have climbed through the roof as the market has eventually warmed up to the idea that his Chevy V8 is at least as potent, and nearly as rare, as the vaunted Hemi.
GM eventually re-used the LS6 name on another engine, but it waited nearly 40 years to do so: the LS6, a 5.7-liter LS motor that appeared in 2001 in the Chevrolet Corvette Z06 before expanding to the engine bay of the Cadillac CTS-V in 2004. Despite having no relation between the design of the small block LS and the big block LS6, each shared the distinction of being produced for a very limited amount of time under the hoods of only a handful of muscle cars.