Chevy Big Block V8
BIRTH OF THE CHEVY BIG BLOCK V8
After the success of the small block V8 launched in 1955, Chevrolet quickly started adding power. 4-barrel carbs, two 4-barrel carbs, hot cams, high compression ratios, and of course cubic inches were all offered up in the name of performance. But as the old saying goes, “Too much is never enough”…especially when you’re talking about horsepower. So Chevy developed a second engine family, larger and more advanced in design than their workhorse small block.
CHEVY BIG BLOCK V8 THROUGH THE YEARS
Right from the start, Chevy’s big block V8 meant business. First off, it was advanced for the times. It used the very successful valvetrain design of the small block, with stamped-steel rockers riding on stud-mounted balls, at a time when most of the industry still mounted its rockers on shafts. But they took it farther than that. The stud-mounting allowed the valves to be staggered, rather than lined up nice and straight. This allowed them to greatly improve airflow. Then they cooked up this crazy idea for putting the combustion chamber in the top of the cylinder (in the block) rather than in the head. Everything in the new big block was designed to make power, big power, and to hold up to the abuse it would surely take. Hence the blocks were thick and beefy, and heavy. But man did they make the power!
CHEVY BIG BLOCK V8s TAKE OVER
By midway through the first generation of big blocks, the Mark I or W-series in 1961, the 409 cubic inch big block was already beating the power made by Chevy’s top engine at the time, the fuel injected 283 small block by a hefty margin, and made tons more torque. By 1965, the “Fuelie” small block had grown to 327 cubic inches and 375 horsepower. Quite an achievement at the time, but even that was not enough to keep pace with the mighty big block. The Mark I 409 in its final year, 1965, in top form with two 4-barrels was making 425 horsepower. Chevy quickly realized that big horsepower was was easier and cheaper to get by building bigger engines, rather than refining smaller ones with tricky technology like fuel injection. 1965 was the last year for the Rochester mechanical fuel injection. From this point on, if you wanted more than around 370 horsepower-or-so, you ordered the big block.
CHEVY BIG BLOCK BECOMES THE STANDARD
With the introduction of the ‘modern’ Mark IV Chevy Big Block V8s in 1965, starting with the 396, thing just got better and better. Chevy’s big blocks came in a variety of outputs, although all with single 4-barrel carbs, as they grew in displacement and output. By the end of the Classic Muscle Car Era (around 1970), the Chevy Big Block was King. Yes, there were big block Fords and Chrysler Hemis running around, and yes they were fast. But over time, and through its prodigious production over the decades, the Chevy Big Block V8 has emerged as the standard big-power American V8, right up through the modern era. Classic car collectors prize original Corvettes, Chevelles, El Caminos and even Impalas that came with big blocks from the factory, and original big block muscle cars command premium prices over similar small block cars.
CHEVY BIG BLOCK V8 TODAY
Over the years, so many aftermarket parts, accessories, tuners, engine builders and racing teams have focused on these stellar engines. Chevrolet Performance came out with an entire line of brand new big block “crate motors” to add fuel to the fire. Many of the fastest dragsters and street racers today run Chevy big blocks, having overtaken the classic Chrysler Hemi as the go-to engine for big horsepower. Despite all the gains made in recent times with turbocharging and other advanced technologies, “there is no replacement for displacement”, meaning the Chevy Big Block V8, now having been stretched beyond 700 cubic inches, is still King!
Mark I Chevy Big Block V8 – 348, 409, 427 (Z11); 1958-1965
MARK I CHEVY BIG BLOCK V8 BACKGROUND
The first version of the Chevy “Big Block” V8 was the Mark I or W-series big block. Introduced in 1958 in Chevy’s passenger cars and light trucks, and running through the 1965 model year in three different displacements, the Mark I Big Block never appeared in the Corvette.
The Chevy Mark I Big Block V8 started out at 348 cubic inches (5.7L), growing to 409 cid (6.7L) in 1961, which ran through the 1965 model year, and appearing in 1962 and 1963 only, at 427 cid (7.0L). The latter is not to be confused with the later 427 Big Block Mark IV engine launched in 1965. Chevy Mark I Big Block V8s (aka: W-series V8s) followed the small block’s basic design layout, but these engines are obviously much bigger than a small block, and heavier, weighing some 665 pounds . They are easily distinguishable by the shape of their valve covers, which are not rectangular. They have sort of a flattened-out “M”-shape to them. There’s nothing else quite like them.
One feature that made the W-series unique was that their combustion chambers were not located in the cylinder head. Instead they were located in the upper cylinder bore, and the cylinder heads themselves served only as a place to seat the valves. The head gasket surface was not perpendicular to the bore (it was angled) such that when the crowned piston neared top-dead center (TDC), together they would form a wedge-shaped chamber with a pronounced quench area, into which the spark plug was inserted. It was a novel design and one that worked quite well to produce gobs of low-end torque, but not so well at higher-RPM operations above 6,000 rpm.
All Chevy Mark I Big Block V8s have cast iron blocks and heads, are “side-oilers” (meaning the crankshaft is supplied with oil by a separate oil galley running low along the drivers-side of the block, rather than fed off the cam), have 2-bolt main bearing caps, and share 4.84-inch (123mm) bore centers. Their Overhead Valve (OHV) arrangement is standard for the times, with one centrally-located camshaft in the V of the block, driven by a chain off the front of the crankshaft. The distributor and oil pump ran off the back of the cam via a helical gearset. The lifters could be either solid or hydraulic, operating hollow pushrods that carried the oil to the top end. Stamped-steel rocker arms ran on stud-mounted balls.
ABOVE: This 1960 Bel Air has the 409 V8 (same as the 348) with single 4-barrel & iron intake. Check out the distinctive shape of the valve cover. This is a dead giveaway that it’s a W-series Mark I Chevy Big Block V8. Ignore the modern AC compressor.
348 CUBIC INCH (5.7 LITER) V8
The first Chevy Mark I Big Block V8 was the 348 (5.7L), launched in Chevy’s 1958 full-size passenger cars cars and light trucks as the “Turbo-Thrust” 348. It had a bore of 4.125” (104.8mm) and a stroke of 3.25” (82.6mm), making for a very oversquare ratio.
The 348 was Chevy’s premium engine from 1958 through 1961, at least in its full-size cars. The fuel injected 283 and the later 327 were really Chevy’s “halo-engines” from 1957 until the Mark II BIg Blocks came out in 1965. But, in top form, the 348 actually made more horsepower and substantially more torque than any small block at the time. (See chart below.) The top-rated 348 in 1960-61 was the Tri-Power version with three 2-barrel carbs making 350 horsepower, at a time when the hottest small block was the fuel-injected 283 (RPO 354) making 315 hp. But by 1961, even 350hp wasn’t enough, so the W-series Chevy Mark I Big Block V8 grew from 348 to 409 cubic inches.
Indicative of the times when gas was cheap and thoughts of tailpipe emissions was nonexistent, there was no 2-barrel option on the 348. If you wanted economy, you presumably either went with Chevy’s Stovebolt-Six or one of the milder small blocks. The 348 was meant to be a performance engine, with either a single 4-barrel in the “Special Turbo-Thrust”, or Tri-Power (three 2-barrel carbs) on the Special Super Turbo-Thrust, providing fuel.
While the 348 has smaller valves and ports, and of course smaller bore and stroke dimensions that the 409 and 427 Mark I Big Blocks, they look identical from the outside, sharing major castings. One simple way to tell a 348 from its bigger brothers is that the oil dipstick on a 348 is on the drivers-side of the engine block, whereas it is on the passenger-side of the block on the 409 and 427 Chevy Mark I Big Block V8s.
348 Mark I Big Blocks
Special Super Turbo-Thrust
Special Super Turbo-Thrust
Special Super Turbo-Thrust
1-4bbl, solid cam
Tri-Power, solid cam
1-4 barrel, solid cam
Tri-Power, solid cam
ABOVE: These 409 heads show why the oddly-shaped valve covers. First, the valves aren’t all lined up, but more important, the spark plugs needed a place to live. Later Mark IV big blocks not only staggered the valves like the Mark I, but also splayed them at sideways angles to improve flow, earning them the nickname “porcupine head”.
409 CUBIC INCH (6.7 LITER) V8
When the max horsepower available from the 348 was no longer sufficient, it became necessary to add displacement by both boring and stroking it. The 348s bore of 4.125″ grew to 4.312” (109.5”), and the stroke went from 3.25” to 3.50” (88.9mm). This bumped the output of the 4-barrel engine to 360hp in 1961, the year of its introduction. By 1962, this same engine with single Carter 4-barrel was making 380hp.
While the 348 had “only” been available with either a single 4-barrel or Tri-Power (three 2-barrels), the 409 also had a dual 4-barrel option on an aluminum intake manifold. In this form, the 409 produced the at-the-time lofty status of one-horsepower-per-cubic-inch, ie: 409hp. It had two Carter AFB carbs, a hot cam, and a forged steel crankshaft. The Beach Boys immortalized this engine in their 1962 hit song “409”. At the time, it was THE fastest car out there. Nothing else had over 400 horsepower, at least nothing that normal people could buy.
By 1963, output had reached 425 hp at 6200rpm with the dual 4-barrel setup, a radical solid lifter cam, and 11.25:1 compression. This was Chevy’s hottest engine by far until the Mark IV Big Block 396 arrived in 1965, at which time the 409 and the entire W-series engine family was discontinued.
There were also versions of the 409 that were less violent. The base 409 had a single Rochester 4GC 4-barrel on a cast iron intake manifold, with hydraulic cam, and normal compression that made 340hp. It was available from 1963 through 1965 when it too was replaced by the Mark IV 396 Big Block V8.
ABOVE: The chrome valve covers on this 1963 409 accentuate their unusual shape, done to clear the spark plugs which entered the combustion chambers at a near-vertical angle.
427 CUBIC INCH (7.0 LITER) Z11 V8; 1963-only
This was a special order engine, available in the 1963 Impala Sport Coupe by checking off RPO Z11 on your order sheet. This was a special package created by Chevy when they were still officially involved in racing and actively backed privateers. Designed for drag racers and NASCAR teams, the package consisted of the 427 Mark I engine, lightweight aluminum body panels, and a working cowl induction hood. The aluminum body parts were fabricated at GM’s Flint Metal Center.
Unlike the later 427 Chevy Mark IV Big Block V8, this 427 was based on the W-series Mark I Big Block V8 architecture in general, and the 409 V8 in particular. The 409 was stroked out to 3.65” (93mm) from the 409s 3.50” stroke. The bore remained unchanged.
Being a super high-performance engine, it came in just one version: full-race. The Z11 had a 2-piece aluminum high-rise intake manifold mounting two Carter AFB 4-barrels, feeding a 13.5:1 compression ratio. It was laughingly underrated at 430 horsepower, it surely made more than that, and 575 pound-feet of torque. Just 50 RPO Z11 427s were built, and another 20 partial engines as replacements, all for the 1963 model year.
Mark II Chevy Big Block V8 – 396, 427; 1963 only
This was the so-called “Mystery Motor” that Chevy was keeping a secret, but slowly feeding to its favorite racing teams. It was basically a W-series Big Block 409 that combined many of the Mark I features along with some of those soon to be introduced in the Mark IV Big Blocks, launched in 1965.
The Mark II Big Block was a one-year only racing engine, which came in both 396 cid and 427 cid, although only the 427 actually saw any racing. They were so much faster than the old Mark Is that they gained the nickname “Mystery Motor”. Racer Mickey Thomson ran a Mark II 427 in his Z-06 Corvettes at the 1963 Daytona 250 and 500, setting records at both events.
Mark III Chevy Big Block V8 –
There was no Mark III Chevy Big Block V8. It was a project that never took off.
Mark IV Chevy Big Block V8 – 396, 402, 427, 454; 1965-present
The Mark IV is the Chevy Big Block V8 most of us think of when we hear the words “Big Block”. There are Big Block Fords, Big Block Mopars, and Big Block Olds, but most people don’t think of them when they hear “Big Block”. The first engine that comes to mind is usually a Mark IV Chevy Big Block V8. These engines also gained the nickname of “Rat Motors”, because the Chevy small block V8 was called the Mouse Motor. A rat’s bigger than a mouse, right? It makes sense.
The Mark IV uses the same basic dimensions as the Mark I W-series engines, with the same bore centers, and main bearing locations, although the main bearing diameter was increased from 2.5” to 2.75”. The Mark IV ended up slightly heavier than the Mark I, at around 685 pounds. But gone were the W-series’ in-block combustion chamber arrangement, replaced by a conventional setup with a 90-degree deck and in-head combustion chambers. The staggered intake and exhaust valves of the W-series V8 remained, although they were now splayed at compound angles. And the arrangement went from E-I-I-E-E-I-I-E (small block-style) to E-I-E-I-E-I-E-I. In other words, the exhaust ports were now spaced evenly, instead of siamezed in the middle, as before. The ports were also enlarged and cleaned up. The angles of the valves were carefully calculated to open away from the cylinder and chamber walls for greater thermodynamic efficiency. They ended up at compound angles to the head surface, creating a look that earned these engines the nickname “porcupine head”. All of this added up to much greater performance at higher RPMs. Because of how the spark plugs were relocated in the new combustion chambers, the valve covers no longer had to be shaped like the Mark I’s. They were now straight along the outer edge instead of scalloped, and quite wide.
The Mark IV Chevy Big Block V8 was substantially beefed up in key areas over its W-series predecessor. The block was thickened in key areas, the crank journals enlarged, the oiling system improved, and the high-performance versions got forged steel cranks and 4-bolt mains. As the result, Chevy’s Mark IV Big Blocks gained a reputation over decades as one of the most robust, reliable and powerful engines every built.
ABOVE: This aftermarket aluminum head shows why they called the Mark IV’s heads “Porcupines”. Notice that the valves aren’t just staggered, and they’re not just angled on one plane. They’re ‘compound-angled’, a complex design that greatly improved thermodynamic efficiency, keeping that big motor breathing right up to the red line.
366 CUBIC INCH (6.0 LITER) V8; 1965-1995
Not of much interest to anyone reading a website called American-Muscle-Cars.net, the 366 Big Block V8 was was Chevy’s gasoline engine for medium trucks and school buses from the mid-1960s through the mid-1990s. It had a 3.935” (99.95mm) bore and a 3.760” (95.5mm) stroke. Designed as a truck engine that would have to take years of abuse, Chevy used four piston rings instead of the usual three. The 366 is unique to Mark IV big blocks in that it has a taller deck height than the 396, 402 and 454, by 0.400”.
ABOVE: This very original 325-horse 396 came without power steering or power brakes, just plenty of muscle.
396 CUBIC INCH (6.5 LITER) V8; 1965-1969
The first true high-performance Mark IV Chevy Big Block V8 was the 396, introduced to the world as the L78 engine option in the 1965 Corvette with 375 horsepower. While this just matched the output of the fuel-injected 327, the new 396 produced way more torque, and at a much lower price. Chevy had discovered that performance was much cheaper to achieve by adding cubic inches than with finicky and expensive new technologies, like Rochester’s mechanical fuel injection system. 1965 was the last year for the “Fuelie”, as the big blocks arrived to take over. From this point on, small block Corvettes focused more on handling, while big block Corvettes focused on brute acceleration. The Chevy big block V8 was a heavy lump of cast iron, much heavier than the small block, that upset the Corvette’s natural chassis balance by dropping too much mass onto the front tires. But who cared. Big blocks, whether in Corvettes, Chevelles, or Impalas, were just plain wicked. Gobs of torque at all RPMs, and yet they could wind.
The 396 had a 4.094” (104.0mm) bore and a 3.760” (95.5mm) stroke. Over the course of its lifespan, it was available in 325hp, 350hp, 375hp, 410hp and 425hp versions, the top-line solid-lifter engines operating well above 6,000 rpm. All had single 4-barrel carburetors, with aluminum intake manifolds on top-line engines. It continued in service as Chevy’s ‘smaller big-block’ until it was replaced by its almost-identical twin, the 402, in 1970. But that’s another story…
396 Mark IV Big Blocks
1965 Z11 Chevelle
Q-jet carb, 10.25:1, iron crank, hydraulic lifters, oval ports, 2-bolt mainsQ-jet carb, 10.25:1, iron crank, hydraulic lifters, oval ports, 2-bolt mains
Holley 800cfm 4bbl, 11.0:1, solid lifters, square ports, steel crank, aluminum hi-rise,4-bolt mains
Holley 800cfm 4bbl, 11.0:1, hydraulic lifters, square ports, steel crank, aluminum hi-rise, 2-bolt mains
2-barrel carb, 9.0:1, hydraulic cam, oval ports, iron crank, 2-bolt mains
325 hp350-360 hp
ABOVE: The 390hp 427 was the ‘entry-level 427’, with cast iron intake and single 4-barrel.
402 CUBIC INCH (6.6 LITER) V8 – 1970-1972
Throughout most of the 1960s, GM self-imposed a limit on all of its divisions that no mid-sized car could have any engine larger than 400 cubic inches (with the exception of the Corvette. The only full-sized GM cars could receive a larger engine. So each division cleverly took displacement right up to the brink on their midsized muscle cars. Buick, Oldsmobile and Pontiac all introduced new 400 cid V8s in 1968. Chevy already had the highly-successful 396 and wisely stuck with it until GM lifted its ban in 1970.
In 1970, they simply took a 396 block and bored it out .030” (0.76mm) which, in an engine this big to begin with, added six more cubic inches, and taking it from 6.5 liters to 6.6 liters. Despite the increase in displacement, Chevy never actually called it a 402 in their passenger car advertising. In its midsized cars it was still called a 396, and in their full-sized cars, they called it the Turbo-Jett 400. The only vehicles where actually called it a 402 were the in light pickup trucks.
Like the 396, the 402 came in a variety of flavors, performance-wise, and pretty much mirrored the 396 lineup. However, the Classic Muscle Car Era peaked in 1970, just as the 402 was being introduced, and every year after would see significant drops in performance due to new and ever-more-stringent government regulations. To cope with unleaded gas, compression ratios dropped drastically, which killed performance. Mandated new smog equipment choked engines off further. Heavy new bumpers and other safety equipment weighed cars down. And, as if weren’t bad enough, starting in 1972, the government required all auto makers to start quote SAE (Society of Automotive Engineers) “Net” horsepower and torque output ratings, rather than the usual SAE “Gross” readings everyone had been using up until now. The Gross number allowed testers to remove all the accessory belts, uncap the exhaust, remove the air cleaner, add race gas, tune the car, and take the best test. SAE Net meant the car had to be tested in real world conditions with everything hooked up, running normal pump gas, and averaging the results. The differences between the two numbers is usually quite dramatic. For instance, the 1971 402 Chevy Big Block V8 was rated at 300 hp SAE gross, but only 260 hp SAE net. A 40-horsepower disparity. So, even if the engines made the same power as before (most didn’t), the advertised horsepower (now quoted in ‘net horsepower’) sounded lower.
Like the 396, the 402 was a very robust, torquey engine that liked to rev…at least at first. Again, 1970 was the best year for everything, including the 402. By 1971, compression was falling, the cam was getting milder, the carb was getting tinkered with, and it just kept getting worse. Production of the 402 ended at the end of the 1972 model year.
402 Mark IV Big Blocks
Q-jet, 10.25:1, hydraulic lifters, oval ports, iron crank, 2-bolt mainsQ-jet, 8.25:1, hydraulic lifters, oval ports, iron crank, 2-bolt mains
Q-jet, 8.25:1, hydraulic lifters, oval ports, iron crank, 2-bolt mains, single exhaust
Q-jet, 8.25:1, hydraulic lifters, oval ports, iron crank, 2-bolt mains, dual exhaust
Q-jet carb, 10.25:1, iron crank, hydraulic lifters, oval ports, 2-bolt mains
Holley 800cfm 4bbl, 11.0:1, solid lifters, square ports, steel crank, aluminum hi-rise,4-bolt mains
330 hp300 hp
160 hp NET
180 hp NET
ABOVE: This 425-horse 427 sits in a 1966 Corvette. This engine and engine compartment appear very original & correct. Note the factory aluminum high rise intake manifold that denotes the 425hp engine.
427 CUBIC INCH (7.0 LITER) V8, 1966-1969
The new Mark IV Chevy Big Block V8 was a bona fide hit, from its introduction in the 1965 model year as the 396. They already had one of the hottest muscle car engines on the market, yet it only took one year for Chevy to up the ante. For the 1966 model year, they started with the 396, the increased the bore from 4.094” (104mm) to 4.25” (108mm) and left the 3.760” (95.5mm) stroke alone. The result was 426.7 cubic inches, an even 7.0 liters. Intended for Chevy’s full-size cars and high-performance Corvettes, the new 427 was offered in a wide range of tunes and outputs, for every application from the mild-mannered station wagon to the fire-breathing Corvette race car. But the mildest of them still had 335 horsepower, so clearly the 427 was not an engine to be taken lightly.
The base 427 was the LS-1 produced in 1969. It had a 10.25:1 compression ratio, a cast iron intake mounting a Rochester Quadajet (Q-jet) carburetor, a nodular iron crankshaft riding in 2-bolt main bearing caps, and a mild hydraulic cam. It made 335 horsepower and probably powered a lot of big Impalas, Caprices, especially the big station wagons of the era.
The L 36 was the start of the performance 427s, an enormous cast iron lump, including a cast iron intake manifold mounting a single Holley or Rochester Quadajet carburetor, hydraulic lifters, 10.25:1 compression ratio, a nodular iron crankshaft, the oval port closed chamber heads and 2-bolt main bearing caps. It made 390 horsepower and boatloads of torque, and was a very fast engine in its day. A ’69 ‘Vette with a 390-horse 427 was nothing to sneeze at. They were fast.
The L68 was basically a 390-horse L36 with Tri-Power in the place of the single 4-barrel. The three 2-barrel carburetors were mounted on a special aluminum high-rise intake manifold, but otherwise the same hydraulic lifter cam, oval port heads, nodular iron crank, 2-bolt mains and 10.25:1 compression ratio carried straight over from the L36. The result was a rated output of 400 horsepower, with the difference being up near the top of the rev-range. The L68 was available only in the 1967 through 1969 Corvette.
ABOVE: The 427 Tri-Power sported three 2-barrel carbs on an aluminum intake manifold, with solid lifers and lofty compression, making 435hp.
Next up the horsepower hierarchy was the L72, the original high-performance 427 Chevy Big Block V8 when it was introduced in 1966. It came with a single 4-barrel, a fairly radical solid-lifter cam, 11.0:1 compression and high-flow square-port cylinder heads, with a forged steel crank riding on 4-bolt mains. Available from 1966 through 1969, it made 425 horsepower and was capable of doing zero-to-60 in around 6 seconds, and the quarter mile in the mid-13s at around 106 mph. Not earth-shattering by today’s high standards, but stellar in 1966.
There was a second, higher-performance Tri-Power 427 also, called the L71. It was basically an L72 with the Tri-Power set up on it. The L72 already had the wild solid-lifter cam, 11.0:1 compression and big heads. So, with the three deuces, the L71 made 435 horsepower and was the most powerful engine available in Chevy’s inventory in a production car. Other rarified racing engines outgunned it, but they were ultra-rare and mega-expensive.
In 1967 Chevy came out with the L89 427, which is one of these rarified racing engines referred to above. It was essentially a L71 Tri-Power 427 with aluminum heads. It was still rated at 435 hp, the same as the L71, because it was essentially the same engine internally. The only difference was the addition of the aluminum heads which apparently made no tangible difference in performance. Their main benefit was reduced weight (approximately 75 pounds) and better cooling when compared to the standard cast iron heads.
As alluded to earlier, Chevy built some very interesting limited-production racing 427 whose very names still send chills down the spines of enthusiasts. The L88 had high-flow aluminum heads with 12.50:1 compression, a wild sold-lifter cam and lots of cool race car internals. They were laughingly underrated at 430 horsepower, but they actually made something north of 500. The other wild racing motor was the ZL1, the all aluminum 427 built for Can Am racing. It was light (for a big block) and even more radical than the L88, yet it was still rated at just 430 horses. A nod to the safety lobby.
427 Mark IV Big Blocks
Q-jet, 10.25:1, hydraulic lifters, iron crank, 2-bolt mainsQ-jet, 10.25:1, hydraulic lifters, iron crank, 2-bolt mains
4-barrel, 11.0:1, solid lifers, hi-flow heads, steel crank, 4-bolt mains
Tri-Power, 10.25:1, hydraulic lifters, iron crank, 2-bolt mains
Tri-Power, 11.0:1, solid lifters, hi-flow heads, steel crank, 4-bolt mains
Tri-Power, 11.0:1, solid lifters, aluminum heads, steel crank, 4-bolt mains
Racing engine, 12.5:1, aluminum hi-flow heads, solid lifters, race cam, racing parts
Racing engine, aluminum block & heads, 12.0:1, solid lifters, race cam, racing parts
335 hp390 hp
ABOVE: The Classic Muscle Car Era peaked with this engine. The 1970 454 LS6, conservatively rated at 450hp, 500+ was more like it.
454 CUBIC INCH (7.4 LITER) V8
By 1970, with the Classic Muscle Car Era at full-throttle and the Horsepower Wars raging, Chevy felt it was time to grow their Big Block V8 again. Little did anyone know that 1970 would be the absolute peak of both the Classic Muscle Car Era and the Horsepower Wars, and that by 1971, compression ratios, and with them horsepower would be on the wane. But, in 1969 as Chevy prepared its new 454 Rat Motor for the 1970 model year, no one knew that yet. It was business as usual, build a bigger engine, more power, more torque, higher RPMs, beat the other guys. The 454 was the perfect answer. Their Mark IV big block had already proven itself and was wildly popular. And it was a very advanced design with its “porcupine”-style compound-angled valve, ahead of most of the American OHV V8s at the time, in terms of sophistication.
And of course, it was easy to expand. The last time they did this, the added bore to the 396 to create the 427, but they left the stroke alone. This time, they left the 4.25” bore alone and added stroke, taking the 396/427’s stroke of 3.760” (95.5mm) and stretched it to an even 4.00” (100mm). The result was 453.96 cubic inches, rounded up to 454, and 7.4 liters of displacement. And it was a monster, and a workhorse, over the years, serving both hotrods and heavy trucks, and everything in between, wherever big power and big torque were needed. And while various mild versions of the Chevy 454 big block V8 were destined for Caprice station wagons and 1-ton pickups, that’s not what we’re interested in at American-Muscle-Cars.net. We want to see muscle car engines, right?
When the 454 launched in the 1970 model year, it was the first year after GM had lifted its self-imposed mandate that no engine larger than 400 cubic inches could rest under the hood of any midsize GM car, with the obvious exceptions of the Corvette and Cadillac. Larger engines were reserved for GMs stable of full-size cars, like the Chevy Caprice. But suddenly you could get a 454 in the midsize 1970 Chevelle SS454.
The LS5 was the workhorse motor, the one you see most often. It made 390 horsepower and a whopping 500 pound-feet of torque. But the true king of the hill, perhaps the Ultimate Muscle Car Motor of the Classic Muscle Car Era may well be the LS6 version of the new-for-1970 454. The LS6 had all the best internals and produced 450 horsepower and 500 pound-feet of torque, or at least that’s what they claimed. Many believe that in reality they had more than 500 horses! Again done for the sake of the insurance companies and the safety lobby. These kinds of numbers, and the real-world performance of the LS6 represented the absolute peak of performance, both claimed and actual, during that Era. In 1970, an LS6-equipped Chevelle SS ran the quarter mile with a trap speed of 106.76 mph, blistering for the day.
But there was one production engine even more powerful, albeit incredibly rare. The LS7 was rated at 465 hp and 610 lb-ft. Later when Chevrolet Performance decided to offer the LS7 as a crate motor, it was officially rated at 500 hp.
As stated before, 1970 was the peak of the Classic Muscle Car Era and the Horsepower Wars, and by 1971, performance was already in decline. Ever more-stringent government regulations controlled everything from safety to fuel economy, exhaust emissions to mandating no-lead fuels. Suddenly Detroit had to change directions, after ramping up displacement, compression ratios and horsepower output year-by-year. For the 1971 model year, GM slashed compression ratios nearly across the board, to deal with the new no-lead fuels. This caused the LS6 to drop to 425hp , and the LS5 to 365hp. By 1972, the LS6 was gone altogether, and the LS5 was fading fast, now making 270 hp NET. This was the year the American auto industry began advertising horsepower output as SAE Net instead of SAE Gross. The result was that the same car had a much lower horsepower number when expressed in SAE Net, so at the same time when power was actually falling, it was appearing to fall even faster. 1974 was the last year a big block was offered in a Corvette and by then it was wheezing out 270hp.
GM introduced EFI (Electronic Fuel Injection) to the 454 in 1987 in Chevy and GM 2500- and 3500-series trucks. As such it made 230hp and 385-405 lb-ft of torque. This was a throttle-body injection (TBI) system, similar to the one Chevy introduced the same year in its small block V8s. In fact they used the same ECM (Electronic Control Module = the engine computer) unit and the same code for the big block, they just upsized the injectors and throttle body to compensate for the added displacement, and it worked great. Imagine how much Chevy must have saved on that one! The Gen IV 454 with TBI continued through the 1995 model year, actually overlapping the introduction of the new Gen V big blocks.
An interesting distinction that the Gen IV Chevy Big Block V8 earned was to be the last GM engine in production to use a carburetor. Because the mighty 454 was so versatile, and so very popular, there was, and remains, a huge market for these torque monsters for boats, RVs, industrial and other applications, and many of them preferred carbureted engines, which GM gladly provided. So, in this instance, the fuel injected 454 was being produced side-by-side with the last of the carb engines, right up until the Gen IV was phased out, in late 1995.
The 454 EFI remained in production until it was replaced in 1996 by the Vortec 7400.
Keyword: Chevy Big Block V8