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Feature Flashback: OG SuperVette – When MT Drove a 10.6-Second C3 Corvette ZL-1

We just ran a 755-hp/715-lb-ft Corvette ZR1 through the quarter mile in 10.8 seconds at 133.1 mph. That’s darned impressive. Wanna know what’s more impressive? The fact that Chevy almost produced a big-block ’Vette for 1970 that would have tripped the lights several feet ahead of this new ZR1—10.6 seconds at 132 mph. Yes, the Corvette ZL-1’s LT-2 successor might have been America’s Ferrari-slayer: With time-slips like that, even Ferrari’s 488 GTB (10.6 seconds at 135.2 mph) would barely be catching 1970 Corvettes on dragstrips today. Would you believe the man responsible for killing Zora Arkus-Duntov’s acceleration monster was none other than that party animal John Z. DeLorean? But let’s go back to a series of articles in 1968 and 1969 and let Eric Dahlquist tell the story.

Chevy’s Heavy Lightweight

In the September ’68 issue, our man Dahlquist got an invite to Bartz Engine Development in Van Nuys, California, for an early look at this all-aluminum hi-po big-block racing engine that was to be homologated with production variants. “There, spread out on newspapers on one of the workbenches, were all the pieces of this latest Chevrolet masterpiece. The block is made from 356 T-6 heat-treated aluminum, using ‘loose-wood’ patterns (like mahogany) that are pieced together. This, as you might guess, is a very limited-production process. The cylinder block is manufactured dimensionally in identical configuration to an L-88 427, except that the walls and main bearing webs are beefed up somewhat.” He went on to note that what he was seeing was a second-gen design, benefiting from revisions to the crank, connecting rods, and L-88-style alloy cylinder heads. He also described the unique dry-sump scavenging arrangement. “The oil pressure pump is located in the aluminum timing cover and was cleverly adapted over from the Turbo Hydra-Matic transmission.”

Some Assembly Required

Al Bartz explained how racers would get their ZL-1 engines: “The engine comes from Chevrolet loosely assembled; that is, all the pieces are bolted together so none are lost during shipment. For $3,000 you get one complete powerplant with L-88 aluminum manifold (PN 3886092). Aluminum water pump, all-gear [instead of chain-driven] reverse-rotation cam drive, reverse-rotation camshaft but no flywheel, clutch, and bell housing. A transistorized reverse-rotation distributor [was] included.” The folks at Bartz then handled blueprinting and final assembly. They also tried other camshaft grinds. Al explained that Chevy’s was “the only grind that will go 7,200 rpm without valve float. At this point we’re getting between 590 and 615 hp (530 to 545 lb-ft. of torque), depending on ram tube length with a modified Lucas/Crower injector. The most significant thing about the engine, though, is that it weighs just 460 pounds ready to go. That’s 40 pounds less than the cast iron 327!”

Love at First Drive

So blown was Dahlquist’s mind when he first drove the ZL-1 that he opened his piece like Rod Serling introducing a Twilight Zone episode: “Button down your mind. Tight. Lock it in place and twist up the safety wire. You’re on a trip to the border of your imagination. The front door of the terminal is the entrance of the nearest Chevrolet Sports Department, and they won’t care if you run.” The next graph was no less hyperbolic: “Sting Ray ZL-1. Say the name over in your mind, amplify it, taste it. It has the same sort of precise tonal delight as Lamborghini Miura or Ferrari 365 GT or Aston Martin DB6, and it is an iron-clad, money-back guarantee that individuality and something called élan, are alive and well in Detroit, at least as long as Zora Duntov is still there.”

A 2G Chaparral for the Street

“The ZL-1 has Ferrari speed plus Ferrari handling and Ferrari brakes, but without Ferrari fuss and bother so you can enjoy it more. Therefore, even without the super Ferrari leather interior and Ferrari coachwork, it is still better than a Ferrari in its own right because there is no distraction and, everything in perspective—aluminum engine, fiberglass body and all—the ZL-1 is nearer a 2G Chaparral for the street.” It must be noted that the car Dahlquist drove was a bit modified—fenders blistered for 14-inch-wide racing slicks on American Racing mag wheels, and straight pipes sans mufflers. “Duntov’s not trying to kid anyone. He knows damn well that a car like this is going to be mag-wheeled, big-tired and raced the hell out of, so why not just offer it to the performance press in its purest form and forget the footwork? That’s why it’s worth something. As debuted, the ZL-1 Sting Ray was ready for all comers in SCCA’s A Production Class or maybe even Le Mans.”

Engine Mods for “Production”

“The all-aluminum 427 cubic inch engine is pretty much the way you read about in the September ’68 issue of Motor Trend when we broke the story on an unsuspecting world, but there are a few refinements. Because gas flow around the valves wasn’t just right, metal was pared away for a new ‘open-combustion-chamber’ design. Then, in order to get the mixture in and out of the new chamber, it was found that by pinching down a bit on the intake porting where it took its bend into the chamber, a venturi effect could be induced so that the flow would not lose velocity.” The valves and porting were tweaked, the compression raised to 12.5:1, and the cam profiles were massaged. The end result: “a complete 550-horsepower ZL-1 427 weighs 20-25 pounds less than a fully assembled 350-horsepower 350!”

A 200-MPH Vette!?

“The ZL-1 doesn’t just accelerate, because the word accelerate is inadequate for this car. It tears its way through the air and across the black pavement like all the modern big-inch racing machines you have ever seen, the engine climbing the rev band in that kind of leaping gate as the tires hunt for traction, find it, lose it again for a millisecond, then find it until they are locked in. From the sharp, banked curve before the start-finish line to the point maybe 1,700 feet down the straightaway, you rocket from 30 to 145 mph at 6,500 rpm. If the car had a higher gear, one of the engineers casually mentions, it will bust 195, possibly 200.”

Best-Handling Corvette EVAR!

“Sorting the handling of this machine should be as easy as writing in RPO F-41 on the order blank. Standard on all ZL-1’s RPO-F41 means you get heavy-duty disc brakes, increased spring rates, front and rear shocks with improved valving and larger capacity in back, plus a fatter front stabilizer as well as one on the rear. All you add yourself are the serious tires and hope the computers at the GM Tech Center have picked the brain of the right memory bank. With a 43/57 front to rear weight distribution. The 2,808-pound car is almost neutral with just a shade of understeer that you can overpower at will with the throttle. It is the best handling Corvette ever built.”

What Price, for Chevy’s Ferrari?

Dahlquist ended his love letter to the ZL-1 by noting, “You must pay a price for the ZL-1 excellence and it is quite high. The cost of tooling an all-aluminum engine of this sort is always dear and these will be hand-built and run in before the car ever leaves the factory. Considering that an L-88 Corvette goes for $6,000, a $9,000 ZL-1 tab is a reasonable figure.” The ZL-1 option ended up retailing for $6,000—the price of a second ’Vette. Only two were sold to the public, but there was to be a successor …

1970 LT-2 454—the Stillborn Successor

Plans were afoot for a stroked, all-aluminum 454 V-8 with most of the ZL-1’s goodies and more. This engine was slipped into a Monaco Orange Corvette for journalists to try out at a press-preview event in the summer of 1969. Motor Trend got to test it a week later, when it was outfitted with a crazy “180-degree” header setup that had two pipes from each bank crossing under the engine to join the other two, so that each collector pipe got a firing pulse every 180 degrees of crankshaft rotation. This produced a ripping flat-plane crank exhaust note, added about 15 hp, and improved fuel economy, but it wreaked havoc on ground clearance. With normal headers the car’s original dyno sheets indicate 588 hp at 6,400 rpm and 542 lb-ft at 4,800 rpm. Spinning through a little Nova torque converter with a 3,000-rpm stall speed, and running wrinkly-sidewall drag slicks, the car was laying down quarter-mile runs of 10.60 seconds at 132 mph. “Which, against a national class record of 10.75 at 128.75, is impressive. The fact that almost anybody who knows how to drive could jump in and duplicate this run after run may be the most shattering aspect of all.” Alas, Chevy was bleeding red ink in those days and John DeLorean was sent in to fix things up. Part of his solution was to de-proliferate the engine catalog. A planned roster of four Corvette Big Blocks was pruned to one—the 390-hp LS-5 454. It cost $289.65 and found 4,473 takers. It slayed no Ferraris.

LT-2 Recreation

In the summer of 2014 we had the privilege of strapping our gear onto a recreation of that mid-1969 press-event Corvette created by Dave Miller. Dave started with an original late-build ZL-1 engine, stroked it to 454 cubes, and consulted extensively with the engineers responsible for creating the original Saturday Night Special. Then with the help of Motor Trend archivist Thomas Voehringer, he and the team at Werner Meier’s Masterworks Automotive in suburban Detroit managed to recreate the car to an incredible degree of accuracy. On a dyno, the new engine registered 625 hp at 6,500 rpm and 545 lb-ft at 5,300 rpm. And on its very first outing—with minimal opportunity for tuning—it managed a 10.86-second run at 124.6 mph. That still beats all the Ferraris we’ve tested, except for the LaFerrari, Enzo, and 488. Of course, Fiorano lap times are a different matter…

Lambo Blogging

Sunday, 1 July 2018

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