Chevy Didn’t Produce the ’70 Corvette LS7, So This Drag Racer Did

Does the new 1250-horsepower, 233-mph Corvette ZR1X get your pulse revving toward redline? In spring 1970, you’d likely have felt the same way about the Corvette LS7. That was the regular production option (RPO) code for what was going to be the car’s top street engine that year, a 460-hp, 454 cu-in version of Chevy’s mighty Mk. IV big-block V-8.

Spoiler alert: RPO LS7 never reached showrooms, but it did become a semi-legendary marker on the Corvette timeline, in a story peppered with surprising twists. The LS7 code itself lived on, first as a somewhat different-spec crate motor and then, in 2006, as the Corvette Z06’s 7.0-liter engine (and later, the 2014–15 Camaro Z/28).

Buckle in, and let’s fire up that four-barrel Wayback Machine.

For 1970, Chevy upsized the 427 cu-in big-block to 454 cubes with a 4.0-inch stroke, up from 3.76 inches. New for 1970, the Chevelle’s Z15 SS 454 package ($503) came with the new LS5 version, rated at 360 hp. For $263 more, nearly 4500 buyers substituted the optional LS6 with a 11.25:1 compression ratio, a huge 800-cfm Holley four-barrel carb, solid-lifter cam, and monster 450-horsepower rating.

The 1970 Corvette offered the LS5, as well, though rated at 390 hp. The LS7 was to be a Corvette-only option with a performance bump over the LS6. It would have been a stunner. The brochure touted the LS7’s “large 4-barrel carb, high-performance cam, mechanical lifters, aluminum cylinder heads and full-transistor ignition system.”

The LS7 shared the LS6’s 11.25:1 compression ratio and 800-cfm Holley carb, the latter with different specs and its own part number. The LS7’s cam had higher lift and longer duration and overlap specs than the LS6’s but was less aggressive than the cam in the 1967–69 L88 427 race engine. Planned transmission choices included a standard M21 four-speed stick or TH400 automatic, with the M22 “rock crusher” four-speed optional.

In December 1969, automotive media test-drove a four-speed LS7 Corvette coupe at Riverside Raceway in California. (Remember that date.) Sports Car Graphic magazine writer Paul Van Valkenburgh was among those who attended.

A couple of months later, while serving Uncle Sam in Vietnam, Chicago drag racer Richard Kachnik read Van Valkenburgh’s account of driving the LS7 Vette prototype 2500 miles from the Riverside event back to Chevy headquarters in Detroit. Along the way, he ran a 13.8-second quarter-mile at 108 mph.

If that run sounds a bit “slow” given the LS7’s lofty specs, it was with two people and luggage aboard, and with a full gas tank. All-in, the car probably weighed around 4000 pounds. What’s more, the car had the standard 3.36:1 axle ratio in its Positraction differential. That mild ratio had other benefits, including the ability to pull from 30 to 140 mph in top gear, according to Van Valkenburgh. He also praised the double-disc clutch, which was essential to handling the LS7’s output and wasn’t a thigh buster.

“Every once in a lifetime,” wrote Van Valkenburgh, “every auto enthusiast ought to be allowed the experience of a long tour in a demon such as this.”

One Man’s LS7 Quest

Van Valkenburgh may have appreciated the 3.36:1 axle ratio, but drag racers who read his story would have been dreaming about what the optional 4.11:1 axle ratio could do for the LS7 in the quarter-mile. Kachnik arranged to have a friend back home in Chicago order a car for him. With a couple months left on his tour in Vietnam, he figured the super-Vette would be waiting when he returned.

It was not. Despite highlighting the LS7 in the 1970 Corvette’s brochure and magazine ads, Chevy cancelled the option not long after the glowing story in Sports Car Graphic. The media car was the only LS7 Vette built, and it was likely crushed, along with the dreams of some Corvette enthusiasts.

Kachnik decided not to buy the less expensive LS5, and life went on. In the late 1960s, before he went overseas, he had worked building drag-race cars. After completing his military service, he started a career in programming and repairing computers. He bought a used Porsche 911 as a fun commuter and still dabbled in racing Chevys. Starting in 1993, he ran an LS7-based Top Alcohol dragster for 10 years with “Hollywood” Richie Amato driving.

“We ran the Midwest circuit around Chicago, Michigan, Minnesota, and Indiana. We did pretty good,” Kachnik recalls. “Before I went into the service, I raced with his brother, who had funny cars.”

A big-block Vette stayed on Kachnik’s mind. In 1990, he bought a highly optioned 1970 coupe, painted Mulsanne Blue, with the LS5. (The color was named for the Mulsanne Straight at Le Mans.) Options included custom interior trim, leather seating, power brakes, power steering, power windows, tilt/telescoping steering column, AM/FM stereo, and factory alarm. After driving the Corvette for a year, Kachnik swapped in an LS6 crate motor.

Meet the New Boss

Like many Vette enthusiasts, Kachnik always figured Chevy had dropped the LS7 due to pending emissions regulations. That was certainly part of the story. Sky-high insurance rates for Vette drivers, especially young men choosing the optional high-performance engines, also worried Chevy’s sales department. But the final nail in the LS7’s coffin was a name that many know well: John Z. Delorean.

DeLorean’s success with driving the Pontiac division to #3 in sales with youthful, alluring cars, including the ’64 GTO and ’69 Grand Prix, propelled him to general manager of Chevrolet, GM’s biggest fish, in December 1969. (There’s that date again.)

DeLorean loved fast, flashy cars, but as head of Chevy he followed a mission to streamline production and address quality-control issues that were triggering recalls and hurting profits. A UAW strike earlier that year worsened matters, delaying production of the 1970 Corvette and second-gen Camaro by four months. That’s why there were just 17,316 Corvettes made in 1970.

While car buyers might have liked the smorgasbord of options Detroit cars typically offered, DeLorean understood how such ample variety amplified production complexity, which in turn could ding quality and cause delays. Some things had to go.

Ed Cole, another “car guy,” had become president of GM in 1967 and axed the Vette’s multi-carb engine options after 1969. As of the 1971 model year, he also required that every GM car be able to use no higher than 91 research octane number (RON) fuel, a change which demanded lower compression ratios. GM also mandated that its divisions publish SAE net horsepower ratings alongside the old, higher gross ratings, which would be dropped for the following model year, 1972.

DeLorean, meanwhile, instituted a “de-proliferation” program to weed out expensive, low-volume options across the Chevy line that added production complexity but gave low return on investment. He reasoned the Corvette did not need five engine choices. Along with three versions of the 350 (300-hp ZQ3, 350-hp L46, and 370-hp LT1), the 1970 Vette brochure showed the LS5 and the wilder LS7 454s.

The LS7 was the first to go in DeLorean’s “de-pro” sweep. By then, it was too late to substitute the LS6 in its place. The Chevelle lost the LS6 for 1971, and the Corvette gained an aluminum-head version of it with lower 9:1 compression. The V-8 still mustered 425 horsepower @ 5600 rpm and 475 lb-ft of torque @ 4000 rpm. (The “as-installed” SAE net hp, published under Cole’s directive, was 325.) Just 188 were ordered—not a surprise, given the option’s price of $1221 (about $10,000 today). That was four times the price of the LS5 that went into about 5100 ’71 Vettes. The sales disparity proved DeLorean’s point.

Even Corvette “godfather” Zora Arkus-Duntov admitted at the time: “Maybe for the street engine, I made a mistake. Aluminum heads are expensive, and that weight doesn’t matter on the street.” The LS6 would not return for 1972. The final big-block Vette came in 1974, and a pair of mild 350s took the Corvette through the 1970s.

Ironically, Corvette sales soared during that “malaise” period, perhaps further vindicating DeLorean, who had left GM in 1973 to start his own car company. Over 50 years later, the Corvette is back to five powertrain choices, but now with retail pricing to cover development and production costs. ($180,000+ Corvettes are now a thing.)

An LS7 Quest Fulfilled

Despite squashing the RPO LS7 option, Chevy for many years offered an LS7 crate motor through dealers. Built for racers, the Chevrolet Performance LS7 (PN 3965774) was a long block (no manifold, carb, or ancillaries). It was a different spec than the cancelled street motor, with iron heads for lower cost and a very high compression ratio of 12:1. 

Around 1990, Kachnik bought two LS7 crate motors for racing, and one of those became the foundation for the engine now in his Vette. He had enjoyed driving the car with the LS6, so turning it into an LS7 was more about fulfilling a long-ago quest than going faster. He also added air conditioning, which was never available with the C3 Vette’s high-revving top performance engine options.

“When I was done with racing in 2003, I started working on the Vette,” he says. “I had used a lot of LS7 stuff in the race car. A lot of parts come and go. I was always saving the good stuff for the future.”

He eventually swapped out his Vette’s LS6 and built up one of his LS7 crate motors, borrowing the LS6’s heads until he found a set of new aluminum heads that he worked up for the car. He also used an LS6-spec carburetor on a factory aluminum manifold and kept a streetable cam, whose spec was a bit beyond that of the LS6’s.

“The really high-lift cams do not produce enough vacuum for pop-up headlight operation, wiper door operation, and all the ventilation controls to work reliably on a street-driven C3 Corvette,” he explains.

The high compression requires airport runs to mix in aviation fuel with 93 AKI pump gas. Kachnik has not dyno’d his LS7 but believes it would easily exceed the RPO LS7’s 460-hp rating from 1970. For the transmission, he stuck with his Vette’s driver-friendly M21 four-speed and did not install an aftermarket double-disc clutch to replicate that part on the 1970 RPO LS7.

More recently, Kachnik refreshed his LS7 tribute Vette for showing. The lacquer repaint done before he bought it in 1990 is still showing well. “It was a very nice car to start. I just wanted everything underneath looking new,” he says.

Decoder Surprise

A member of the National Corvette Restorers Society (NCRS), Kachnik researched his 1970 Vette’s origin when he gave it the refresh. He got a surprise when he ran the car through NCRS’s database to get the build and delivery information: “Dealer: 500” and “Zone: Zero” codes. 

“That means the car was delivered right back to GM headquarters in Detroit,” he says. “NCRS has maybe less than a dozen cars in their database with that dealer code and zone.”

Those codes usually identify cars requisitioned by engineering for testing, or by marketing and public relations departments for photo shoots and media test fleets.

“The LS7 prototype would have been processed like that and would likely have had those codes, so it’s like a bonus connection back to that.”

Today, Kachnik is happy to take his unique Vette to local shows and cruise nights. The car attracts attention for its color and condition, though he says the special engine goes unnoticed by most. 

“A lot of people don’t know the LS7 history. Sometimes, when I step away from the car, I might see a couple of guys looking at it for a half-hour. They’re the ones that know all the nuts and bolts. And then it’s like 50 questions.”

He’s happy to answer all of them.