NOTHING EXCEEDS LIKE EXCESS. When the Olds 4-4-2 first arrived in 1964 it was hailed (by those who got to know it) as a balanced performer, combining horsepower with weight distribution, handling, and braking. The 4-4-2 continued to offer that balance as it evolved but, let's be honest, there was a big section of the market who weren't interested in balance—they were interested in acceleration. Oldsmobile knew it. Witness this ad copy: "You roll up to the light next to the cocky-looking guy in the supercar. He gives it a couple blips…then looks you over."
That's not the start of two gentlemen about to take a spirited drive down a twisty road. That's two teenagers, or 20-somethings, or older guys who still think like young guys, about to have it out, on the street, stoplight to stoplight. The recipe for dominating the competition there and at the drag strips was spelled one way only: power-to-weight ratio.
The conventional 4-4-2 offered between 325 and 360 horsepower from its tall-deck 400-cu.in. Oldsmobile V-8, depending on which transmission was selected and whether the W-30 "Force- Air" package was ordered. That was plenty to make a sporty, fun-driving car. But it wasn't enough to tackle, oh, say an L78 396 Chevelle or a 440-powered GTX. That's where the Hurst/ Olds comes in.
While Chrysler Corporation let you waltz into a dealer and order up a Charger, Coronet R/T, or GTX with a 440 or even a Hemi, General Motors was attempting to be a good corporate citizen and didn't permit its largest engines to be used in intermediate-size cars as a regular-production option. Different divisions found different ways around this. Chevrolet snaked some 427 Chevelles through using GM's Central Office Production Order (COPO), while others were created at the dealer level at places like Yenko, Nickey, and Berger.
Beneath the dual-snorkel hood lurks an all-iron, 455-cu. in. V-8. The sealed-to-the-hood air cleaner is another part not shared with the 4-4-2.
What Olds did was set up a fiction whereby Demmer Engineering, a privately owned Lansing, Michigan, company, "installed" a red-painted and chrome-valve-cover-bedecked, 380-hp (and 500 lb-ft!) L32 455, an optional engine from the fullsize 88 model (where it was rated at 390 horsepower), in a limited number of 4-4-2s, and then lavished them with special paint, badges, and a Hurst Dual Gate shifter to produce the Hurst/Olds. The reason this was a fiction is that, while Demmer did the cosmetic work, the actual 455s (and associated heavy-duty cooling system, front disc brakes, and TH400 transmission) were quietly installed right at the Oldsmobile factory before the cars were shipped to Demmer.
Original H/O 455 engines have a number of distinguishing features, including a one-year-only intake manifold, cast-iron, but reportedly otherwise identical to 1970's aluminum W-30 intake; and cylinder heads coded with a "D" or a "C." On paper, C-code heads were for A/C cars, but in practice any car could get either head. Most H/O's received D-code heads, though legend holds that C-code heads actually flow better.
The Hurst/Olds first appeared for the 1968 model year, when it was a bit of a sleeper, wearing silver paint from the Toronado line and little in the way of flashy graphics, air scoops, etc. For 1969, however, it was decided to throw conservatism out the window and embrace the excessive nature of a 455-powered A-body. While the initial prototypes went even further (see this month's coverage of the Muscle Car and Corvette Nationals for the recently restored prototype), the gold-and-white paint scheme would become a hallmark of Hurst/Olds editions through 1979.
Other distinguishing exterior features include a yawning scoop atop the hood (matched up with a special air-cleaner base not shared with W-30 4-4-2s—those ducted air from up front via hoses), molded from fiberglass and adorned with "H/O 455" callouts on both sides ("And you watch the creeping horror of realization hit him," went the ad, "'That's more than a 4-4-2…it's a '69 Hurst/Olds!'"), a trunk-mounted pedestal spoiler, body-color "racing mirrors," and 15-inch (a H/O exclusive size) Super Stock II wheels that had been bathed in chrome rather than painted gray as on most other Cutlasses. The wheels were originally accented in Argent Silver, but many were re-finished in Hurst Fire Frost Gold before or after sale. Black-painted 4-4-2 grilles, black pinstripes, H/O emblems on the front fenders and decklid, and G60-15 Goodyear Polyglas tires rounded out the car's public face.
Inside, driver and passengers sat in vinyl bucket seats shared with the 4-4-2, but were reminded that they occupied "more than a 4-4-2" not only by the shifter, but by a "Hurst/Olds" emblem on the glovebox and gold stripes on the headrests. For comfort, buyers could option air conditioning; for keeping an eye on the engine, most did option the U-21 "Rocket Rally- Pac" tach, clock, and instruments. The shifter and its mini-console, though, were the stars of the show.
"Punching that big Hurst Dual Gate Shifter up through the gears," was said by Oldsmobile's ad folks to be "half the fun of owning a '69 Hurst/ Olds." With the manual selection of gears in the mandatory M41 "Heavy- Duty Turbo Hydra-Matic 400," most buyers didn't miss the four-speed that wasn't available in the H/O.
The Turbo 400 spun the same heavy-duty driveshaft as came in regular 4-4-2s, which was in turn connected to an Olds-specific 12-bolt (10 bolts in the ring gear) axle packed with a standard Anti-Spin (limited-slip) differential and one of three gearsets: 3.42:1 was standard gearing for non-A/C cars, 3.23:1 was standard for A/C cars, and 3.91:1 was optional for non-A/C cars.
Other chassis elements remained unchanged from the 4-4-2, including the four-link, coil-spring rear suspension. All 4-4-2s received front and rear anti-sway bars and boxed lower rear control arms. All four corners also received heavy-duty springs and shocks right on the production line, with no changes made by Demmer.
Are you persuaded by all the extras that were packed into the Hurst Olds? If so, happy hunting. You'll be looking for one of between 906 and 913 cars, including one prototype (shown elsewhere in this issue) and three convertibles (one of which was destroyed while new and replaced). No matter how many were built, it's as the ad guys said: "Awesome is the word for it."
ENGINE
All Hurst/Oldses received the same 380-hp, 455-cu.in. engine that had been installed in air-conditioned H/ Os in 1968 and optionally available in the Oldsmobile 88 with slightly different accoutrements. Because they did not share a fresh-air routing with the W-30 equipped 4-4-2, the H/O 455 used a unique air-cleaner base, very similar in design to those used on the Ford Cobra Jet, to seal the Rochester Quadrajet to the hood scoops. The original engine should have a nine-digit code, the last six of which are shared with the VIN.
TRANSMISSION
A heavy-duty TH-400, topped with a Hurst Dual Gate shifter, was the only way H/Os came equipped in 1969. An original transmission will have a code of "OH," a date code of "69" for the model year, and a sequential serial number for the trans stamped on a tag on the right-hand side of the case. The left-hand side will be stamped with the same partial VIN as on the engine block. A heavy-duty driveshaft, shared with the 4-4-2, mates this to an Oldsmobile-specific 12-bolt (10-bolt ring gear) rear axle geared according to the chart found on page 76.
Mirrors, headrest stripes, and the Hurst Dual/Gate shifter with its wood-grain mini-console are all H/O-only details. Many were also ordered with Rocket Rally-Pac instrumentation.
INTERIOR
A black vinyl bucket-seat interior from a 4-4-2 received refinements like gold stripes on the headrests, a "Hurst/ Olds" emblem on the glovebox door, and, of course, the Dual Gate shifter with small Hurst console. Most also had the U-21 "Rocket Rally-Pac" combination tachometer, clock, and gauges. First owners had the option to send in a "registration" card and would receive an engraved plaque for the interior in return; 603 did, and some cars have that plaque in place.
CHASSIS
The already-excellent chassis of the 4-4-2 with its heavy-duty shocks and coil springs, four-link rear setup, anti-sway bars front and rear, boxed lower control arms, and front disc brakes was used unaltered under the H/O. The H/O's only wheel used an Argent Gray, 14-inch Super Stock II center in a stepped, chrome 15 x 7 rim. Many dealers and owners changed the Argent Gray to Fire Frost Gold to match the stripes. Goodyear Polyglas tires in G60-15 were original equipment and are conveniently offered as reproductions today.
BODY
The most-obvious Hurst/Olds visual is the Cameo White paint with Fire Frost Gold stripes (convertibles have the gold stripe painted directly on the white top material) and black pinstriping. Next most obvious is the H/O exclusive Outside Air Intake with its prominent "H/O 455" callouts on either side. Other hallmarks include three badges, a spoiler, and blacked-out 4-4-2 grilles. The "English Racingstyle" mirrors are the same as found on the 1969 AMC Hurst SC/Rambler, as are the air-cleaner flapper door and vacuum motor.
PRODUCTION
It is widely accepted that 906 H/O hardtops (out of a planned 700) were built for the general public. Other production includes three convertibles: two built for promotional purposes during the original production run, one of which was destroyed in 1970. A replacement for that car was subsequently built. Another unknown number, perhaps up to six, prototype and pre-production cars were also built— the latter for use by Hurst executives. The final count may be as high as 913 H/Os built out of more than 26,000 4-4-2s produced.
REAR AXLE CODES
| CODE | GEARING TYPE | RATIO |
|---|---|---|
| SJ | Standard non-air conditioning gearing | 3.42:1 Anti-Spin |
| SH | Standard air-conditioning gearing | 3.23:1 Anti-Spin |
| SL | Optional non-air conditioning gearing | 3.91:1 Anti-Spin |
Recent
Photo: Richard Prince
1963 Corvette RPO Z06
The fuel-injection fender emblems tell you this car is equipped with the potent 360-horsepower Rochester fuel injected 327-cu.in. engine, but nothing on the exterior indicates that this is an ultra-rare 1963 Z06 Corvette.
Photo: Richard Prince
When the second generation Corvette was introduced in model year 1963 this workaround to keep Chevy’s sports car racing in spite of the AMA ban manifested itself with an option package called Z06. A 1963 Z06 Corvette included virtually all of the same type of high performance equipment offered since 1957 but for the first time it brought all of the individual assemblies and components together in one option package. This initially included a 360-horsepower fuel injected engine, 4-speed manual transmission, Positraction rear axle, heavy-duty suspension (stiffer front and rear springs, stronger shock absorbers, and larger front anti-roll bar), heavy-duty brake system (heavier, vented backing plates, front cooling scoops, Cerametallic linings, finned drums, and dual-reservoir master cylinder with power assist), 15”x6” cast aluminum quick take-off wheels, and 36.5-gallon fuel tank. In December of 1962 however the aluminum wheels and large fuel tank were eliminated from the package and made separate options. This reduced the cost for Z06 from $1,818.45 to $1,293.35.
It's interesting to note that Z06 was initially available for coupes only but approximately concurrent with the deletion of the aluminum wheels and 36.5-gallon fuel tank the racing option package was also made available for convertibles. Chevrolet production records indicate that a total of 199 Z06 Corvettes were produced in 1963. The vast majority of these were coupes but it’s likely that a small number (fewer than ten) convertibles were built. Approximately 75 Z06 coupes were equipped with a 36.5-gallon tank. Whether or not any 1963 Corvettes, including any Z06s, left the St. Louis assembly plant with quick take-off aluminum wheels is uncertain because production of the wheels by supplier Kelsey Hayes was delayed owing to porosity in the castings and loosening of the retaining nuts. It is indisputable that some of the very first Z06 coupes, which were delivered to owners of experienced race teams, including Delmo Johnson (owner of Johnson Chevrolet in Dallas, TX) and Grady Davis (Executive Vice President of Gulf Oil), competed with aluminum wheels but these were supplied after the cars were delivered. Extant GM documentation relating to the wheels indicates that up to 13 1963 Corvettes may have been factory-equipped with them and if so, it’s probable that all or nearly all of these were very early pilot line cars.
Photo: Richard Prince
2001-'05 Corvette Z06
When the C5 Z06 model was introduced in 2001 it was available as a hardtop only, because this configuration was stiffer and lighter than the coupe or convertible.
Photo: Richard Prince
When unveiled for model year 1963, "Z06" was an option package and the nomenclature was consistent with the designations that GM typically used for its many options across all of its brands. Long before the term was revived in 2001 however it had transcended just another option code and came to symbolize an ultra-high performance, race-ready model designation. In other words, “Z06” took on a life all its own and came to be universally understood among enthusiasts as a very special model of Corvette. Recognizing this, Chevrolet formalized it with the introduction of a distinct Z06 model in 2001.
The C5 Corvette hardtop served as the starting point for Z06 because it was the stiffest (by 12 percent) and lightest (by 80 pounds) body structure being produced. Power for the C5 Z06 was supplied by the LS6 engine, which featured improved bay-to-bay breathing via cast-in windows in the block, pistons cast from high-strength M142 aluminum alloy, new, better breathing intake and exhaust manifolds, new cylinder head castings, a more aggressive camshaft, higher rate valve springs for a higher redline, and higher capacity fuel injectors.
All C5 Z06s were powered by an LS6 engine, which featured improved bay-to-bay breathing via cast-in windows in the block, pistons cast from high-strength M142 aluminum alloy, high-flow intake and exhaust manifolds, more efficient cylinder head castings, a more aggressive camshaft, and higher capacity fuel injectors. The engine was rated at 385 horsepower when introduced in 2001 but rose to 405 horsepower the following year.
Photo: Richard Prince
The LS6’s initial rating was 385 horsepower but that grew to 405 horsepower in 2002. The increase came from a new catalytic converter featuring reduced back pressure. With less back pressure engineers were able to make further gains in the induction system with a new air cleaner, a revised mass air flow sensor, and a higher lift camshaft.
All Z06s benefitted from a bespoke six-speed manual transmission, called M12. It had more aggressive gearing and a temperature sensor to help protect it from higher thermal stresses. Z06 also had its own suspension system, called FE4. It featured a larger diameter front stabilizer bar, stiffer rear leaf spring, and revised camber settings, all calibrated for better handling during high speed operation.
Rocker ducts that direct cooling air to the rear brakes quickly distinguish a C5 Z06 from the base cars.
Photo: Richard Prince
Z06 handling was also improved by virtue of special wheels and tires. Besides being an inch wider, the uniquely styled wheels were the most mass-efficient ever produced for Corvette to that point, which is to say their strength-to-weight ratio was the highest. These light-yet-strong wheels were wrapped with Goodyear Eagle F1 SC tires that were wider and stickier than the Eagle F1 GS EMT tires on coupes and convertibles. The Z06 tires were also lighter than their counterparts, reducing total mass by 23.4 pounds.
Reducing the weight of Z06 was a major concern for Corvette engineers, so in addition to lighter wheels and tires, Z06 also benefitted from several other unique features. The first-ever use of titanium in the exhaust system of a mass-production car saved 17.6 pounds and another 5.7 pounds was eliminated by means of a thinner windshield and backlight.
The stiffer structure, added power, more aggressive gearing, tuned suspension, grippier tires, and reduced weight yielded the fastest, best stopping, and best handling regular production Corvette built to that point in time. A C5 Z06 can hit 0-60 miles per hour in 3.9 seconds, turn 12.4 second quarter miles, peak north of 170 miles per hour, and generate 1.03g of lateral acceleration.
2006-'13 Corvette Z06
The C6 Z06 was offered only as a coupe and under the skin differed markedly from its base counterpart by virtue of an aluminum body structure.
Photo: Richard Prince
One year following the 2005 introduction of Corvette’s sixth generation a new Z06 was made available. The hardtop body was discontinued so the C6 Z06 was offered only as a coupe. The heart of this Z06 was a small new block engine dubbed LS7. It featured a 4.0-inch stroke and 4.125 inch bore that together yielded 427 cubic inches. For maximum durability LS7 used forged aluminum pistons, a forged steel crankshaft, and forged titanium connecting rods. These exotic rods were 30 percent lighter than the steel rods used in the base Corvette’s LS2. Six-bolt main bearing caps secured the crank, and a dry sump lubrication system ensured its bearings got a steady stream of oil. The stout short block was capped with CNC-ported aluminum heads and a composite intake manifold. Each LS7, hand-assembled by an individual master engine builder in GM’s new Performance Build Center in Wixom, Michigan, produced 505 horsepower and 470 pound-feet of torque.
The hand-built LS7 was mated to a revised Tremec T56 six-speed transmission, featuring stronger internal parts to survive the engine’s power output. Likewise, the Z06 chassis, crafted from aluminum instead of steel like the regular C6, was upgraded with stiffer springs and recalibrated Sachs shocks, a larger diameter rear anti-sway bar, and larger Speedline wheels wearing Goodyear F1 Supercar EMT tires, sized at 275/35ZR18 up front and 325/30ZR19 in the rear. For upgraded stopping power the Z06 got a new brake system. Up front, huge 14.0 inch vented and cross-drilled steel discs were squeezed by six-piston calipers while at the rear, 13.4-inch steel disks were fitted with four-piston calipers. Each piston in each caliper got its own brake pad, for a total of 20 individual pads. Though complicated, this unusual setup aided brake cooling and reduced the potential for uneven pad wear.
The Z06’s performance was advanced by lower overall mass in spite of some things that added weight, including its dry sump oiling system and larger brakes, wheels, and tires. The biggest weight savings came from the Z06’s aluminum chassis, which eliminated a full 136 pounds compared with the standard car’s steel structure. Carbon fiber front fenders, a floor made from balsa wood sandwiched between carbon fiber sheets, cast magnesium structures for the engine cradle and roof, and elimination of a removable roof panel together eliminated slightly more than 60 pounds. The use of less sound insulation for the cabin and substitution of manual seat adjustments for the otherwise standard electric seats cut another 33 pounds. All told, the Z06 tipped the scales at about 50 pounds less than a standard C6. This helped make the C6 Z06 the highest performing Corvette that Chevrolet ever produced until 2009, when the ZR1 was unveiled.
Photo: Richard Prince
All C6 Z06 LS7 engines were hand-assembled by an individual master engine builder in GM’s Performance Build Center in Wixom, Michigan.
2014-'19 Corvette Z06
With a C7, for the first time in Corvette’s history, the Z06 model was available as a coupe or convertible. This was made feasible by advances in design, construction and materials that made the convertible body structure every bit as strong and stiff as its coupe counterpart.
Photo: Richard Prince
The seventh generation Corvette, introduced in model year 2014, was the ultimate expression of the marque’s front-engine architecture. In fact, the new C7 was so good that the base car delivered performance comparable to the C6 Z06. This raised the engineering goals for the C7 Z06 significantly and by all accounts the Corvette group really nailed it.
All of the exterior features unique to C7 Z06s, including its wider stance and rear spoiler, were driven by functional considerations.
Photo: Richard Prince
Corvette Chief Engineer Tadge Juechter directed his team members to aim for a new Z06 that equaled or surpassed C6 ZR1 performance in every category. This led to the adoption of a supercharged V8 for the C7 Z06. Dubbed LT4, the forced-induction mill delivered 650 horsepower from 6.2-liters of displacement, and it did so in a very efficient way that integrated smoothly with the overall Corvette assembly process. Key to minimizing changes to the C7’s structural design and assembly line flow was a supercharger compact enough to fit under the standard hood, yet potent enough to reach the engine’s power targets. Such a supercharger didn’t exist, so they worked with supplier Eaton to create one. The newly designed R1740 TVS was 10mm shorter and 10mm smaller in diameter than the LS9 supercharger found in C6 ZR1s, eliminating any need for a hood bulge. Though design changes such as different rotor spacing and higher speed – it spins up to 20,000 rpm, 5,000 more than the supercharger on the LS9 – yielded greater efficiency the smaller supercharger did squeeze less air than the larger unit used on the LS9, 1.74-liters of air per revolution instead of 2.3-liters. To meet the power goals in spite of lower boost the engine team devised a very efficient flow path going into the supercharger and developed an improved discharge port that minimizes turbulence, reduces heat and speeds up airflow through a more efficient intercooler.
With the C7 Z06, fresh ingested through the grille went through a tilted radiator and the supercharger’s intercooler before exiting out the louvered hood vent. By going up through the hood rather than down and underneath the car the airflow contributed to downforce rather than lift.
Photo: Richard Prince
While the Z06 LT4 was built with the same engine block as the base LT1 it used many bespoke parts to handle higher cylinder pressures and added horsepower. These included titanium intake valves, stainless steel cast exhaust manifolds, a modified cam, and improved pistons.
Similarly, the LT4 cylinder head design was essentially the same as the LT1 heads but the LT4 units were more durable. They were rotocast from a special A356T6 aluminum alloy that was stronger and better able to withstand high heat. Heat management was also aided by a larger capacity oil cooler for the otherwise standard Z51 dry-sump oiling system.
C7 Z06’s LT4 engine used a newly designed, highly efficient supercharger to help generate 650 horsepower from 6.2-liters of displacement.
Photo: Richard Prince
While all prior versions of Z06 were available only with a manual transmission, Chevrolet decided to offer the C7 Z06 with an automatic. The existing six-speed automatic was not strong enough so the transmission engineering group at GM Powertrain, led by Bill Goodrich, were put to work designing a new transmission. Compared with the six-speed automatic it was to replace, the new unit had to be lighter, strong enough to withstand the supercharged engine’s enormous torque production, no larger and preferably smaller, and better performing in all measures, and it had to do all of this at approximately the same cost as the six-speed. The result, designed with the aid of the most advanced computer tools then available, was an all-new eight-speed automatic that made extensive use of aluminum and magnesium.
The base C7 Z06 came with Michelin Pilot Super Sports while the optional Z07 package equipped Z06s got Michelin Sport Cup 2 tires. In both cases they were sized at P285/30ZR19 up front and P335/25ZR20 at the rear.
Photo: Richard Prince
In addition to the new 8-speed automatic, which was manufactured in GM’s Toledo Transmission plant, the new Z06 was also available with a seven-speed manual gearbox. As with the base Stingray, manual transmission cars came equipped with Chevrolet’s Active Rev Matching system.
All C7 Z06 exterior design changes, including its wider stance, were driven by functional considerations first and foremost. The base Z06 came with Michelin Pilot Super Sports while the optional Z07 package equipped Z06s got Michelin Sport Cup 2 tires. Either way, they were sized at P285/30ZR19 up front and P335/25ZR20 at the rear. Z06 got its own lightweight, spin-cast aluminum wheels measuring 19x10 inches in front and 20x12 inches in the rear.
Z06 designation on the bottom of the steering wheel immediately tells you this C7 is the high performance Z06 model.
Photo: Richard Prince
As a track-oriented car, added cooling capacity for the engine, transmission, differential, and brakes were another important consideration in the car’s exterior design. Very large front fender vents exhausted more air from the engine compartment and unique air blades over the inlets on top of the rear quarters channeled about 50 percent more air into the transmission and differential cooling ducts than those on the Stingray. The wider Z06 rear fascia had larger exhaust ports adjacent to the tail lamps to help move the added air volume out. Ducts that took in air at the corners of the grille cooled the front brakes while scoops in front of the rear wheel openings directed air to the rear stoppers.
Also consistent with its track focused design, the C7 Z06 was the highest street-legal downforce car GM every produced, and the highest they’ve every tested, which is to say it generated more downforce than any competitor car GM tested, including of course exotics costing many times what the Z06 cost.
All C7 Z06s had increased downforce by virtue of air ingested through the grille going through a tilted radiator and the supercharger’s intercooler before exiting out the louvered hood vent. By going up through the hood rather than down and underneath the car the airflow contributed to downforce rather than lift.
The LT4 used in the C7 Z06 was built with the same engine block as the base LT1 found in standard C7s, but it used many upgraded internal parts to handle higher cylinder pressures and added horsepower. These included titanium intake valves, stainless steel cast exhaust manifolds, a modified cam, and stronger pistons.
Photo: Richard Prince
Beyond the vented hood, exactly how much downforce a C7 Z06 produced depended on which of the three available aero packages it had. In its standard state the Z06 aero parts included spats around the front wheel openings, the aforementioned hood vent, and the same upright rear spoiler found on Stingray’s Z51 Performance Package. The second aero stage consisted of a carbon fiber package, available in either black or a visible carbon fiber finish. This package included a carbon front splitter with aviation-style winglets, carbon rocker panels, and a larger, three-piece rear spoiler with fixed wickerbills. The wickerbills are small, vertical tabs at the edges of the spoiler’s blow-molded center section that measurably increase downforce. The third and most extreme aero configuration came from the optional Z07 package, which included a number of special aero components. At the front owners could install either of two different size carbon winglets for the front splitter and at the rear there was a tall, center wickerbill that featured about 25mm of adjustment. This wickerbill was clear so that it didn’t interfere with rearward vision when adjusted to its highest position.
2023-Current Z06
Though the C8 E-Ray accelerates quicker, the C8 Z06 offers the best all-around performance of any Corvette produced thus far.
Photo: Richard Prince
It was a foregone conclusion from its inception that the mid-engine C8 lineup would include a Z06. As with the transition from C6 to C7, the base model C8 delivers performance comparable to the prior generation’s Z06, so the C8 Z06 had to meet extremely ambitious performance targets. To achieve this, engineers optimized its engine, drive train, suspension, brakes, wheels, tires, and aerodynamic features.
After nearly seventy years of development Chevrolet’s small block V8 was approaching the limits of its power potential so engineers started with a clean sheet of paper and designed a highly advanced new powerplant for the C8 Z06. Dubbed LT6, this new V8 displaces 5.5 liters and produces 670 horsepower at 8,400 rpm and 460 lb-ft of torque at 6,300 rpm. These figures make it the most powerful naturally aspirated V8 ever offered for a production car.
The C8 Z06 engine is an all new design that uses a flat plane crankshaft to maximize power and efficiency. The nylon chambers atop the C8 Z06’s LT6 engine each have a volume equal to the engine’s 5.5-liter displacement. Three computer-controlled valves between the two plenums open and close to take advantage of the natural pressure waves induced by the action of the intake valves, allowing the amplitude of the air in the plenums to be magnified, which delivers volumetric efficiency greater than 100 percent.
Photo: Richard Prince
The new engine’s cylinder case and oil sump are made from aluminum and mated at the crankshaft centerline. In a stark departure from all previous GM engines the LT6 utilizes a race-inspired 180-degree flat-plane crankshaft. This type of crankshaft is lighter than a conventional cross-plane crank, which enables it to spin up quicker and rev higher. A flat-plane crank engine is also inherently more efficient because the exhaust pulses in each cylinder head are spaced 180-degrees apart, something that enables it to move more air through. This benefit is optimized with precisely designed, upward sweeping Y-shaped stainless steel headers.
Additional features of the engine that contribute to its incredible performance include forged aluminum pistons, forged titanium connecting rods, and four overhead camshafts with adjustable, computer-controlled camshaft drive sprockets that allow for 55-degrees of timing variability for the intake valves and 25-degrees for the exhaust valves. The engine’s aluminum heads feature four valves per cylinder and CNC machined intake ports and combustion chambers.
The C8’s interior - for all models, including Z06 - is the highest quality, in terms of materials and workmanship, ever offered for Corvette.
Photo: Richard Prince
The engine’s induction setup includes twin 87mm throttle bodies that meter air to molded-nylon plenum chambers. The chambers each have a volume equal to the engine’s 5.5-liter displacement. Three computer-controlled valves between the two plenums open and close to take advantage of the natural pressure waves induced by the action of the intake valves. By controlling these pressure waves the induction system benefits from a phenomenon called Helmholtz Resonance and magnifies the amplitude of the air in the plenums, effectively forcing the intake charge into the cylinders and allowing the engine to exceed 100-percent volumetric efficiency. This yields a torque curve that remains very close to peak output of 460 lb-ft all the way from 3,500 rpm to the LT6’s 8,600 rpm redline.
The LT6 engine is coupled to the base C8’s Tremec TR-9080 eight-speed, dual-clutch transmission but for the high performance Z06 it’s fitted with a lower, 5.56:1 final drive ratio for quicker acceleration. The electronically controlled limited-slip differential optional for Stingray is standard with Z06. GM’s fourth generation Magnetic Ride Control (MRC) suspension, introduced as optional for the Stingray in 2020, was also made standard with Z06. For Z07-equipped Z06s MRC gets a unique calibration that enhances track performance.
The C8 Z06 was optimized to deliver maximum track performance in a car that can still be driven comfortably on a daily basis.
Photo: Richard Prince
To take full advantage of the MRC 4.0 suspension Z06 is fitted with more aggressive bodywork that measures 79.7-inches wide, which is 3.6-inches wider than the Stingray. This provides the necessary clearance for 20 x 10-inch front and 21 x 13-inch rear forged-aluminum “spider” wheels, which are available in five different finishes. Michelin Pilot Sport 4S ZP tires sized at 275/30ZR20 and 345/25ZR21 respectively are standard fare while the optional Z07 package includes even stickier Michelin Sport Cup 2 R ZP tires that were developed specifically for Z06. In either case, the front tread is 1.18-inches wider than Stingray tires and the rear tread is 1.57-inches wider, contributing to the car’s superior handling and more aggressive appearance.
For increased stopping power Z06 gets a bespoke Brembo brake system, with larger 14.6-inch-diameter front and 15-inch-diameter rear rotors and six-piston front calipers, compared to Stingray’s four-piston calipers. Brakes are further enhanced with the Z07 option, which utilizes vented, cross-drilled carbon-ceramic rotors and compatible pads. The fronts measure 15.7 x 1.5-inch and the rears are 15.4 x 1.3-inch.
To contend with added heat a Z06 can generate when pushed hard on a track engineers specified several important cooling upgrades. The unique Z06 front fascia includes larger air intakes and draws clean air into a central heat exchanger, one of five located throughout the car to provide additional cooling air to the engine, brakes, and transaxle. The wider rear fenders also allow for larger air intakes than those found on the base car.
When equipped with the optional Z07 package and adjusted for maximum effect, a C8 Z06 produces up to 734 pounds of downforce at 186 mph.
Photo: Richard Prince
Besides adding cooling capacity, Z06’s bespoke bodywork also improves aerodynamic performance. And as with the C7 Z06, multiple levels of aerodynamic trim are available with the new Z06. The base setup features a front splitter and rear spoiler with a removable wickerbill that generates up to 365 pounds of downforce at 186 mph. Aero performance is enhanced with the optional Carbon Fiber (RPO CFZ) and Visible Carbon Fiber (RPO CFV) Performance packages. Corvettes equipped with CFZ or CFV can also get an optional Carbon Aero Package with large rear spoiler and front dive planes, which increase downforce. Called TOF/TOG, the Carbon Aero Package is required with the Z07 performance package.
The highest performing aero package for Z06 comes with option Z07, which includes a larger front splitter, front corner dive planes, a rear wing, and underbody strakes. When adjusted for maximum effect, the Z07 aero components deliver up to 734 pounds of downforce at 186 mph.
In a first for any GM vehicle, carbon fiber wheels are optional with the Z07 package. The one-piece composite wheels save about 41 pounds of unsprung mass compared with the standard aluminum wheels.
Conclusion
Every C8 Z06 engine is hand-assembled by one artisan who proudly puts his or her name on a plaque that mounts between the LT6’s nylon plenum chambers.
Photo: Richard Prince
When the Z06 option package was introduced in 1963 it set new levels of performance for Corvette. Over the six-plus decades since then Z06 models have continued that legacy, giving buyers a lighter, faster, better handling and quicker stopping car that is equally at home on the street or on a road racing course.
Photo: Jesse Kiser
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