The original ZR-1 was a heavy-duty racer option offered in the '70-1/2 to '72 Corvettes. From the outside, the car looked like any other LT-1 Vette. The ZR-1 option included the LT-1 engine, the M22 four-speed transmission, heavy-duty power brakes, transistor ignition, an aluminum radiator, special springs, shocks, and stabilized bars, as well as a long list of creature comfort deletes. The ZR-1 option prepared the ground work if you wanted to go racing.
In '90 the ZR1 name was resurected and powered by the exotic LT5, all-aluminum, double-overhead-cam engine built by Mercury Marine. To handle the extra power, the largest street tires of the day were included. To cover the wide tires, the entire rear section of the car was widened. Called "The Super Vette" the ZR1 was Chevy's performance flagship from '90 to '95.
The '09 ZR1 is an excellent example of how racing can improve a car. Lessons learned from the successful C5-R and C6.R racing programs were poured directly into this latest ZR1 Corvette. Powered by the 600-horsepower, supercharged LS9 engine, the ZR1's top speed is estimated to be close to 220 mph! Zero-to-60 comes up in just 3.5-seconds and quarter-mile times are close to 11-seconds flat!
The ZR1 will likely carry the C6 Corvette through it's production run. We'll be talking about this Corvette for a long time. Will the current C6 ZR1 get an AWD system? Will there be a C7 ZR1 down the road? We'll see.
Illustrated Corvette Series No. 132 - 1970-1/2 - 1972 ZR-1 Corvette
"The Original ZR-1"
By 1970, the Detroit horsepower party was largely over, and GM management was planning radical changes for ‘71 and beyond. There was a growing awareness of the health hazards of breathing fumes from leaded gasoline, along with increased pressure from insurance companies to curb the escalating output of domestic cars. But while the GM brass were putting the kibosh on performance, Zora Arkus-Duntov was doing his best to keep it alive.
In February of ’69, John DeLorean was top dog at Chevrolet. Knowing the direction that GM president Ed Cole had mandated, DeLorean and his Corvette product planners were tasked with creating a new theme for the Vette: the luxury sports car. The Custom Interior Trim option cost just $158 and included leather seats, woodgrain trim on the console and door panels, and special carpeting. This was just the beginning of the added creature comforts that would define the Corvettes of the ‘70s. .
But Duntov wasn’t about to let the hard-core performance crowd go without some goodies to race with. The L-88 was history, and the ZL-1 was only available as a crate motor. The hot new performance engines were the LT-1 350 small-block and the LS5 454 big-block. If racing was your intention, there was the LT-1–based ZR-1 option, along with the (planned) LS-7-based ZR-2. Unfortunately, the ZR-2 never made it into production in ‘70, but it did make a brief appearance in ’71 with a somewhat detuned 454 LS-6. The ‘71 model year was the only one for the $1,747 ZR-2 option, with just 12 units produced. The cure for the lower-compression LS6 was simply a set of dome-top pistons. The ZR-2 was the base car for John Greenwood’s entry into road racing in the ‘70s.
The ZR-1 and the ZR-2 were officially designated as “off road,” which translated to ”racing only.” Like the ’67 to ‘69 L-88 cars, the ZR Corvettes were not happy on the street, but they did provide an excellent base on which to build SCCA Class A or Class B racers. The ’70 ZR-1 package cost $968 and included the following: the solid-lifter, 370-horsepower LT-1 engine; an M-22 four-speed transmission; heavy-duty power brakes; a transistor ignition; a special aluminum radiator; a metal radiator shroud; and special springs, shocks, and front and rear stabilized bars. There was also a long list of options that were not available. These included power windows, a rear-window defroster, air conditioning, power steering, deluxe wheel covers, an alarm system, an AM/FM radio or stereo, and an automatic transmission. Racing fender flares were included in the trunk space, and a cold-air scoop and header-type side exhausts were sold separately. As with the L-88 package, Duntov wanted to discourage customers from buying a car that wasn’t designed for street use. There were 25 ZR-1 units built in ‘70, 8 units built in ’71, and 20 units built in ‘72. When the 454 ZR-2 option was released in ’71, only 12 units were built. All of the "ZR" Corvettes were built by Chevrolet’s “Repair Department” in St. Louis.
The ‘70-1/2 Corvette also received a minor makeover. There was the revised, egg-crate grille that matched the new egg-crate side vents, square front turn-signal lights, rectangular exhaust tips, and flares on the back edges of the front and rear wheel openings. The LT-1 and ZR-1 options included the big-block hood with special pinstriping and “LT-1” lettering. Positraction and tinted glass were standard, and there was no charge for transmission choice.
It would be 18 years before the ZR-1 name would resurface in ’90, and another 19 years before the ‘09 version showed up. It was definitely worth the wait! - K. Scott Teeters
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lllustrated Corvette Series No. 82 1990 ZR1 Corvette
Whether is was deliberate or accidental, Chevrolet milked the automotive press for nearly two years with the ZR-1 Corvette! It was the biggest power leap since the introduction of the big-block engine in 1965.
The ZR-1 conversion was much more involved than simply dropping a larger engine under the hood. The biggest challenge had to do with actual production. The original idea was to have a set of double-overhead-cam heads made that would replace the stock Corvette heads. But they soon discovered that the extra width from the new heads made it impossible to install the engine on the assembly line. Changing the assembly line or the frame was not an option. So the decision was made to have a completely new engine developed.
Since GM owned Lotus, work began in May 1995 by Lotus engineers to design a new engine for a super-Corvette. The new engine would be designed to fit into the Corvette assembly line, but the overall package would be far from cheap. Unlike the Cosworth Vega's DOHC bolt-on heads, the new LT5 would be a fresh start.
Even though the introduction was delayed because Chevrolet wanted to get it right, the finished product was stunning. The L98 Corvette engine had 245 horsepower, the ZR1 packed 375 horsepower! The engine had four overhead-cam shafts and 32 valves. The heads used a fast-burn cloverleaf design with centrally located spark plugs. The intake manifold had 16-runner inlets and two Multec injectors per cylinder. It had a direct-fire ignition with camshaft sensors and used 12 quarts of oil. The ZR-1 was a jewel of an engine.
To handle the extra power, special 315/35 ZR17 Goodyear Z-rated tires were mounted to 11-inch wide rims. To cover the larger tires, new body panels were made to replace the stock doors, rear fenders, rear fascia, and upper rear panel. The taillights were rectangular, as were the exhaust tips. All of the Z51 suspension parts were standard.
The ZR-1 was a real bear. It ran the quarter-mile in 13.4-seconds and 0-to-60 in 4.9-seconds and. Top speed was 171mph. Despite the $58,8741 price, it didn't stop 3,049 customers from buying a 1990 ZR-1. - K. Scott Teeters
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lllustrated Corvette Series No. 97 1995 ZR1 Corvette
"End of the Line for the ZR1"
All good things come to an end, right? The ZR-1 was arguably the most aggressive engineering effort ever put into production in the entire history of street Corvettes. It's a miracle and a mystery that the Corvette is even alive in General Motors. When you hold the stodgy, bean-counting nature of GM up against the $31,258 ZR-1 option, it's even more amazing. Remember, this is a company that has put the Corvette on the chopping block many times since 1953. It just goes to show you what affection, passion, and love of a high performance automobile can do to even the most conservative corporate decision makers. The late '70s and early '80 was like a bad dream.
Despite the basic nature of GM, there were enough performance hounds working at top levels that saw the value of buying Lotus Engineering in the '80s. Thanks to Lotus' expertise in building and developing exotic all-aluminum engines, the Corvette team had the resource to design a state-of-the-art, world class, exotic American V8 engine. In sports car circles, Corvettes had always carried the stigma of its "basic" pushrod Chevy engine. The ZR-1 absolutely put an end to all that nonsense.
When the ZR-1 was being planned and developed, the Chevrolet Marketing Departments optimistically projected at least 5,000 units per year. Since the entire run of ZR-1 cars from 1990 to 1995 amounted to only 6,939 units, from a business viewpoint, the ZR-1 was a dismal failure. But from a performance and status perspective, the ZR-1 was a stunning success.
In the late '80s the "collectibility" craze was in full-swing. The ZR1 was supposed to be an '89 model option, but was delayed due to minor certification problems with the engine. All this did was stoke the magazines and the collectors. When the ZR-1 finally arrived as a '90 model, some dealers sold the cars with steep markups. Five years later, they were selling ZR-1s at steep discounts. Chevrolet marketing guru Ed Cole said, "The problem with sports cars is you have to sell all of them the first day"
Aside from the new front fender gills and a few other details in the base Corvette, the '95 ZR-1 was a carryover. To sweeten the ZR-1 package, the Z07 Selective Ride Control and the low tire pressure tire warning system options were now included. The most noticeable visual change in the '95 ZR-1 was the 17-inch, 5-spoke alloy wheels. Mercury Marine, the manufacturer of the ZR-1 engine, had completed production of ZR-1 engines in November 2003, so the '95 model still had 405 horsepower. And remember, that is "net" horsepower, not like the olden days of unrealistic "gross" horsepower ratings. The gross power rating for the ZR-1 was at least over 500. This shows up in the ZR-1's 111 mph speed after a 13.1-second quarter-mile blast.
So why didn't the ZR-1 become the "to die for" Corvette of the early '90s? It boiled down to aesthetics, price, and the increasingly high standard of the base Corvette. The ZR-1 had dedicated rear body parts to cover the huge 11-inch wide rear wheels. Except for the restyled rear fascia and a slight curve on the front of the rear wheel openings, the ZR-1 looked like a regular Corvette. Then in '91, all Corvettes had similar styled tail lights. So except for minor details, the ZR-1 looked like a regular Corvette.
Then there was the price issue. While no one could argue about the ZR-1 engine, a single option costing almost as much as the car was more than most buyers would accept. Yes, the ZR-1 could run with Europe's big dogs, but it didn't look exotic, it looked like a regular Corvette. And finally, as the base car got quicker and faster, the performance gap got to the point where the price wasn't worth the performance gain. But it sure looked good with the hood open.
The ZR-1 provided valuable know-how that showed up in the '97 LS1 engine for the new C5. Also, let's not forget the Morrison Motorsports 1991 record-smashing, 171.885mph ZR-1 Corvette. The ZR-1 helped put to rest that tired, old rant from the European crowd that the Corvette was nothing more than a pretty Chevy. - K. Scott Teeters
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Illustrated Corvette Series No. 133 - 2009 ZR1 Corvette
"Chevy's World-Class Supercar"
The Internet rumor mill worked three shifts for nearly two years on the recently introduced ‘09 ZR1. Fuzzy spy photos kept fans stoked, while all sorts of colorful names were bandied about. The buzz was that the Corvette team was hard at work on a new super-Vette. The only solid information was that the car would be based on the existing Z06. Everything else was up for delicious speculation. Automotive bloggers and magazine writers taunted us with names such as “Blue Devil,” “Stingray,” “Corvette SS,” and “Z08.” Then, in December ‘07, Chevrolet stopped torturing us and announced the return of the king: The ZR1 was back!
The new ZR1 is arguably the most aggressive production Corvette ever made. As we wrote last month, the ZR1 name was originally a racing option from ’70-1/2 to ‘72. The ’90-‘95 ZR-1, with its jewel-like LT5 engine, was a terrific machine, but it didn’t look that much different from a regular Corvette. Such is not the case with the latest ZR1. One has to go all the way back to the ’65-’69 big-blocks—with those amazingly loud side-mounted exhaust pipes—for more visual testosterone. The ‘09 ZR1 bears a strong resemblance to the L88 Corvettes, with their flared fenders and race-car-inspired details.
But unlike the earlier super-Vettes that were intended for track use only, this is a mega-muscle machine you can live with everyday. Forty years after the L88 and ZL1, we now have a Corvette that delivers unimagined performance in every area. Let’s draw some comparisons.
The new ZR1 packs 620 horsepower and 595 pound-feet of torque. The L88 and ZL1 engines never received accurate published power ratings, but real output was estimated to be close to 550 gross hp. The new ZR1’s LS9 engine is rated in net hp. It also passes emissions tests and is capable of over 20 mpg on the highway. The beasts of old got 8-10 mpg and had no emissions controls whatsoever. The new ZR1 also has a suspension that won’t hammer out your fillings and brakes that don’t have to be hot to work. Yes, 40 years of development have paid off big-time.
The ZR1’s stunning good looks are obvious from every angle. While the Z06 is a very aggressive-looking car, the ZR1 takes things to the next level. The entire front end and the roof section are made of carbon fiber. Chevy decided to show off the exotic material by using a $60,000-a-gallon clearcoat over the new chin spoiler, rocker panels, front fenders, and roof. The new hood is one inch taller than a regular Vette’s, bears a slight resemblance to the C3 big-block hoods, and features a Plexiglas window that shows off the LS9’s engine cover. The front and rear fender flares are the same as the Z06’s, but the front fenders have larger, more aggressive vents. The back end is finished off with a short, full-width spoiler. The only things missing are the side-pipes, rendered unnecessary by the car’s ultra-efficient conventional exhaust system. New ZR1 badges adorn the front fenders and rear bumper cover.
The new ZR1 couldn’t have much more exotic hardware. The all-aluminum LS9 engine is not only supercharged, it has an intercooler, port fuel injection, a 10.75-quart dry-sump oil system, and a LUK dual-disc clutch. The TR6060 six-speed transmission has been beefed up, and the gear ratios are closer than those in the Z06.
Now let’s talk about those wheels and brakes. The Speedline forged-aluminum wheels measure 19x10 inches in the front and 20x12 inches in the rear. For the first time since ’77, a Corvette will not be wearing Goodyear tires. The Michelin Pilot Sports measure 285/30-19 on the front and 335/25-20 on the rear. The brake system uses Brembo carbon-ceramic rotors that are vented and cross-drilled. They measure 15.5x1.6 and 15x1.4 inches fore and aft, respectively. Six-piston calipers are employed in the front, and four-piston units are used in the back. The brake pads are twice the size as those used on the Z06 and will last the car’s lifetime in street use. The basic Z06 suspension is modified with next-generation Delphi Magnetorheological (MR) variable shocks, softer springs, larger anti-roll bars, and revised rear-suspension geometry.
The interior has only slight addThe interior has only slight additions. The seatbacks feature “ZR1” embroidery, a boost gauge and “ZR1” tach face plate spruce up the instrument cluster, and the door-sill plates also bear the car’s model designation. And so you don’t forget how fast the ZR1 can take you, the speedometer goes up to 220 mph!
The interior has only slight additions. The seatbacks feature “ZR1” embroidery, a boost gauge and “ZR1” tach face plate spruce up the instrument cluster, and the door-sill plates also bear the car’s model designation. And so you don’t forget how fast the ZR1 can take you, the speedometer goes up to 220 mph! - K. Scott Teeters
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Illustrated Corvette Series No. 134 - 2009 ZR1 LS9 Engine
"GM's Civilized Monster-Mouse"
It’s not just about the numbers, folks. Sure, if you compare the famous big-block 427 ZL1 with the 376ci LS9, the conclusion is obvious. The ZL1 never had accurate published power ratings (estimates were in the 550hp “gross” range) and would have never passed current durability requirements, much less EPA certification. The new LS9 does all of the above and produces significantly more power considering that its (minimum) 620hp rating is a more accurate “net” figure.
But the LS9’s superiority is about more than just numbers. In the old days, when big-blocks were bold, if Duntov wanted more power, all he had to do was add a little more of everything. That meant more cubic inches, extra compression, hotter spark, colder air, and/or additional carburetion. It was all a juggling act between maximum power, driveability, and durability. And we won’t even get into fuel economy.
ZR1 Corvette production is scheduled for only 2,000 units, beginning in July of 2008. All LS9 engines are hand-assembled at the GM Performance Built Center in Wixom, Michigan. This powerplant was three years in development and makes major advancements through the use of cutting-edge engine-management systems. These “black box” electronic wonders help balance out the radical hardware while ensuring emissions compliance and respectable fuel efficiency.
Those willing to pony up 100-plus grand will get prodigious output along with a relatively mild cam grind that makes for a very stout but tractable vehicle. After all, the ZR1’s stated goal was to be a docile pussycat around town and a track-day tiger. At 1,000 rpm the LS9 is already making 300 hp and 320 lb-ft of torque, with maximum readings of at least 620 hp and 595 lb-ft coming at 6,500 and 4,000 rpm, respectively. Incredibly, ninety percent of the LS9’s peak torque is available from 2,600 rpm to 6,000 rpm. For an EPA- and GM-durability-certified engine, that’s damn impressive!
Let’s go through the basics and see how this mouse roars from beginning to end. The LS9 displaces 6.2 liters, with bore/stroke measurements of 4.06 x 3.62 and a 9.1:1 compression ratio. The engine is a pushrod, 2-valve-per-cylinder design with a 12-quart dry-sump oiling system. The block and cylinder heads are aluminum, but the heads are spun-cast from A356-T6 alloy for higher heat tolerance.
The LS9’s block is essentially the same as the base LS3’s, but nearly all other components are either completely new, upgraded LS3, or LS7 parts. Reinforced bulkheads improve block stiffness by 20 percent. The LS9 uses six-bolt steel main caps with high-strength steel bearing caps, a new forged-steel micro-alloy crankshaft, and a new 9-bolt flywheel mount. The head-gasket design is unusual, too. The gaskets are cut to the same shape as the LS3 units but have four layers of steel instead of two. Also, the intake tract incorporates a “swirl ring” to improve the air/fuel mixture.
I know what you’re thinking: Why didn’t they just use the 427ci LS7 to start with? Designed for use in the naturally aspirated Z06, the LS7 block was rejected because its thinner cylinder walls prompted durability concerns with the added pressure from the supercharger. Maybe we’ll see that setup in the C7 Corvette.
When it comes to making power, it all begins with copious amounts of compressed, cooled air. That air enters the intake tract and travels straight into a new Eaton R1900 2-rotor supercharger nested between the cylinder banks. Each of the blower’s rotors has four lobes, making it both efficient and quiet. Using a 2.3:1 pulley ratio, the Eaton unit pumps out 2.3 liters of compressed air per revolution and achieves a maximum boost level of 10.5 psi.
The compressed air is transferred to a “dual brick” Behr air-to-liquid intercooler capable of reducing intake-charge temperatures by as much as 140 degrees F. It is then blown through valves that are the same size as the LS3’s but use titanium construction on the intake side and sodium-filled stainless steel on the exhaust. The pistons are forged aluminum instead of cast, and the connecting rods are machined out of titanium.
Standard LS3 ignition coil packs mounted to the rocker covers ignite the pressurized mixture. A unique, electronic fuel-pressure regulator switches between 87.0 psi and 36.3 psi settings based on engine speed, while an 11-rib V-belt runs the supercharger, power steering, and water pump.
Keeping a high-pressure, high-temperature engine such as the LS9 engine alive requires enhanced oiling capabilities. In addition to its dry-sump system, the LS9 is the first small-block Chevy to use oil squirters to boost cooling and reduce engine noise. The exhaust system of the LS9 is identical to the Z06’s, with manifolds and catalytic converters designed to meet 150,000-mile durability tests. No official EPA fuel-mileage ratings have been published to date, but the LS9 may fall victim to the gas-guzzler tax.
The ZR1’s drivetrain has also been enhanced with a twin-disc Luk clutch that has dual 260mm discs. It boasts more clamping power than the Z06’s single 290mm unit, with no extra pedal effort. Power then runs through a revised TR6060 six-speed manual gearbox with dedicated ratios, including a steep First gear that helps launch the car and a shorter Sixth gear to enable the ZR1’s 200-plus-mph top speed.
It wasn’t long ago that even racing Corvettes didn’t have this much cool hardware. But then again, there’s never been a $100,000-plus Vette available from your local Chevy dealer. If you haven’t yet placed your order, you just might have to wait for the ‘10 model. Will the ZR1 coast through the rest of the C6 run unchanged as the flagship Corvette, or does Chief Engineer Tadge Juechter have a few more tricks for the ZR1? Stay tuned! - K. Scott Teeters