Mark IV big-block development reached its
peak in 1969 with the release of perhaps the most mythical of all rat engines -- the
all-aluminum ZL-1 427. A direct by-product of Chevy’s back-door involvement with Jim
Hall in Can-Am racing, this engine featured an aluminum block, cylinder heads, intake
manifold and water pump, and could be considered an all-aluminum L-88 with a few minor
tweaks. A complete ZL-1 weighed some 160 pounds less than the standard cast-iron 427. With
a 12.5:1 compression ratio, a radical mechanical camshaft with .579” intake,
.620” exhaust lift, duration figures of 354° intake and 334° exhaust, and the
expected Holley carb atop the high-rise intake, the ZL-1 was considerably more powerful
than the factory rating of 430 horsepower. In fact, Chevy claimed 500+ hp was just a set
of tubular headers away.
 At
450 hp, the 1970 LS-6 454 holds the distinction of having the highest output rating of any
Chevy production engine. |
This very special engine was installed in just 69 Camaros in 1969 (under COPO 9560),
and approximately 8 Corvettes.
In 1970, Chevrolet increased the size of the Mark IV big block to 454
cubic inches, and released yet another legendary big-block engine. The LS-6 454 was
certainly the most potent big block available to the average enthusiast. Most of the other
“special” big blocks were built in very small runs, and in many cases the local
Chevy dealer didn’t even know they existed. Everyone, however, knew about the LS-6. A
forged steel crank spun in 4-bolt mains. Heavy-duty connecting rods featuring 7/16”
bolts were connected to forged, domed pistons yielding an 11.25:1 compression ratio.
Rectangular port cast-iron heads with 2.19” intake and 1.88” exhaust valves were
topped with an aluminum intake and Holley carb. The intake used was a low-profile unit,
which certainly cost some horsepower but allowed the engine to be installed in the
Corvette with its very low hood line. The mechanical camshaft was the same piece used in
the 396/375-horse and 427/435-horse engines. Power production of the LS-6 was
450-horsepower, which gives the beast the distinction of being the most powerful Chevrolet
engine installed in a production model (at least according to factory ratings). Although
initially earmarked for the Vette, the engine is actually most closely associated with the
1970 SS 454 Chevelle. A Super Sport Chevelle with the LS-6 is certainly thought of by
Chevy fans as the ultimate muscle car, and it’s hard to argue with them.
Continue to Motown Muscle pg.7
(Chrysler) |
