These days we tend to think of the ZR1 as the top dog in the Corvette ecosystem, but back in 1971, an even more capable Corvette could be had, provided you had the wherewithal (and the funds) to select the ZR2 package on the order form. But to get a clear picture of how the ZR2 came to be, we have to wind the clock back a few years prior.

When the new third generation Corvette debuted in 1968 it was a significant aesthetic departure from the C2 Stingray it replaced. Taking inspiration from the Mako Shark II concept car, the C3 was essentially identical to the C2 mechanically, but its body and interior were all new. This meant that the numerous drivetrain options from the C2 could be carried over to the C3, including a multitude of big block V8 options.

Externally the ZR2 didn’t look much different from the garden variety big block Corvettes of the day. But installed in the engine bay was a power plant that defied the downward trend of performance in 1971, and underneath that alluring body work was some serious competition-grade hardware designed specifically with road racing prowess and durability in mind.

In the C3’s inaugural year of production, the L88 427 was perhaps the most sought-after power plant. Available on the sly from 1967-1969, the L88 was a motor developed specifically for motorsport with little concession toward daily drivability on the street. Compared to the other 427s in the Corvette lineup, the L88 featured a bigger carburetor, a higher compression ratio of 12.5:1, aluminum heads, and a unique induction system.

But this wasn’t the first time a clandestine, motorsport-derived options package had become available to Corvette buyers – starting as far back as 1956 with the “SR” options package, enthusiasts in the know could spec out their Corvettes with components pulled directly from Corvette racing program and operate these cars on the street. Yet knowing what the “ultimate” performance package was still took some insider knowledge.

For instance, although the L88 is considered the most potent high performance motor you could get from the factory in 1968, the L71 427’s official horsepower rating was higher at 435 hp versus 430 for the L88. The general consensus is that this was likely a ploy by Chevrolet to convince casual enthusiasts to focus their obsession on the version of the 427 that was designed for street use, though the fact that the L88 options package cost nearly twice that of the L71 (at $947.90) probably raised more than a few confused eyebrows back in the day.

1969 would see the return of the L88 option, although its days were numbered, as Chevrolet had been busy developing an even more potent version of the motor. Unleashed mid-year, the ZL-1 improved upon the L88 with an all-aluminum engine block, beefier connecting rods, and open-chamber heads that out-flowed the L88’s.

But the ZL-1 options package was hair-raisingly expensive and required a number of heavy-duty options to be included, a sum which essentially doubled the price of a Corvette from base configuration. As a result, just 94 ZL-1 engines were built in 1969, two of which would be used in actual ZL-1 package-equipped Corvettes while the rest were sold to race teams.

Zora Arkus-Duntov, GM’s star performance engineer and the man credited for molding the Corvette into a world-class sports car through the 1950s and 60s, knew that looming EPA regulations would quickly spell the end of the ZL-1 program, and sure enough, the options package did not return for the 1970 model year. This left a conspicuous gap at the top end of the Corvette performance portfolio, as the new top-spec motor that year was the 390-horsepower LS5 454 by default.

Although it would be easy to assume Arkus-Duntov had simply stopped pursuing the development of a ZL-1 successor, the reality is a bit more complicated.

First, the debut of the LT-1 was capturing the attention of enthusiasts in 1970. Factory rated at 370 horsepower, this high-revving small block screamer boasted a forged steel crankshaft, 4-bolt main block, solid lifters, a high-lift camshaft and other requisite go-fast goodies, like an aluminum intake manifold and a big four-barrel carb.

Although less than ten percent of all Corvettes made in 1970 would be fitted with the LT-1, it was none the less a critical success, with various publications of the day favorably comparing the LT-1 equipped Corvette to the best that Europe had to offer.

The second factor that contributed to the lack of an “ultimate” big block in 1970 was the LS7 454. Slated for production and discussed in Chevrolet literature at the time, the motor was expected to develop in excess of 460 horsepower in the Corvette but option never made it to production, with Chevrolet ultimately offering the LS7 as a crate engine instead.

Although the LS7 was set to debut in the Corvette in 1970, it never actually made it to production. This left an absence at the top of the heap of big block performance for the Corvette, though the introduction of the LT-1 small block, and the ZR1 package that used that potent small block, keep hardcore enthusiasts and would-be road racers satiated.

Another reason that enthusiasts’ attention was being drawn away from the big block cars was the debut of the new ZR1 package. Available exclusively with the LT-1 motor, the ZR1 included a host of road racing-caliber equipment pulled from the L88 part bin, including the M22 “Rock Crusher” close-ratio four-speed, the J56 heavy-duty brake package, the F41 suspension package and an uprated cooling system that consisted of a bigger aluminum radiator and an expansion tank. Like the L88 before it, the ZR1 would prove to be a rarely-ordered options package, with just 25 examples built in 1970 and even fewer over the next two years after.

But rarer still is the 1971 ZR2. The ZR2 was the eventual (and final) answer to the L88 that had come before it. Available for only one year, the ZR2 included all the equipment from the ZR1 but instead of a small block LT-1 under the hood, buyers were treated to a new LS6 454.

Although the muscle car era was already starting to feel the pressure of emissions controls, the LS6 dished out a conservatively rated 425 horsepower despite its 9.0:1 compression ratio, resulting in performance that was observed to be comparable with the legendary L88.

As was often the case with competition packages available on street cars of the day, ZR2 customers would have to forego luxuries like air conditioning and the a radio if they wanted to the pinnacle of Corvette performance in 1971.

Just 12 examples would be outfitted with the ZR2 package in 1971, and only a pair of them were built in convertible configuration. By 1972 the ZR2 was gone, making these beasts among the rarest high performance Corvettes in existence. Not surprisingly, they’re also some of the most sought-after vintage Corvettes around, with a recent auction seeing their values approaching half a million dollars.