Courtesy of Mecum Auctions

  • One of three Motion Performance Corvettes built in 1973
  • Custom bodywork and numerous special Motion Performance features
  • 350-ci engine with 425 dyno-tested horsepower
  • Reworked Turbo 400 transmission
  • Center console, T-tops and letter of authenticity signed by Joel Rosen, aka “Mr. Motion”
  • The only 1973 Motion Performance Corvette Manta Ray GT known to exist

SCM Analysis


Years Produced:1973
Number Produced:25,521 (three Motion GTs)
Original List Price:$5,562 (base)
SCM Valuation:Median to date, $13,600; high sale, $110,000 (this car)
Tune Up Cost:$300
Distributor Caps:$35
Chassis Number Location:Plate on lower left windshield pillar
Engine Number Location:On block in front of right cylinder head
Club Info:NCRS
Alternatives:1965 Chevrolet Corvette 327/375 L84 coupe, 1967 Chevrolet Camaro Z/28, 1969 Chevrolet Corvette 427/435 L89 coupe
Investment Grade:C

This car, Lot S119, sold for $110,000, including buyer’s premium, at Mecum’s auction in Harrisburg, PA, on July 23, 2016.

During the leisure-suited 1970s, many a third-generation Corvette “shark” was sacrificed on the altar of custom culture. This was the era of wide lapels, bell bottoms, twinkling polyester and such, and the era’s custom cars were likewise made to strut, wearing massive fender flares, big spoilers, diamond-stitch interiors, and heavy-flake paints. Any Corvette was widely seen as simply a starting point — a blank canvas just waiting to be turned into the newest custom.

Of course, aftermarket tuner companies were in on that game, as there was money to be made, even if it was in small numbers. American hustle, indeed! But among them, at least in terms of custom C3 Corvettes, Motion Performance was one of the first, starting its GT program in 1969.

Portal to the 1970s

Some sticklers for original Corvettes may find this Motion Performance-modified Corvette an abomination, but I’m a fan. And not because I find its modifications to improve Bill Mitchell’s original vision for this Corvette generation attractive, but because this restored custom is an authentic view into the 1970s, when flared-fender Corvettes and Camaros, shackled-up Mustangs and Montegos, and shag-wagon Chevy, Ford and Dodge vans were not laughable and anachronistic, but genuinely cool.

In the 1970s, mods like these were totally fair game because they increased the value and desirability of a vehicle during a period in which its core value was spiraling downward, as used cars nearly always do. Today, however, it’s a different story. Imagine cutting up an original C3 to build a custom just as the market is recognizing the model more and more for its inherent value. Even Bill Mitchell himself might not have it.

Aging well

The car world’s tastes do change, but while most Corvette collectors and Corvette shops go where today’s interest and money is — restorations and resto-mods — it is refreshing to see period-correct modified Corvettes starting to be restored to faithfully honor their place in time. And looking good was what they were all about.

But there’s a difference between your average custom ’70s Corvette and this Motion car, and that’s the fact that this example was sold as-new by Motion Performance as a complete package. Motion Performance was known for building high-performance, strip-ready cars for the street. Started by Joel Rosen on Long Island, NY, in the early 1960s, the firm became indelibly connected with Baldwin Chevrolet.

This car has always been a Motion car, and it’s a rare one at that — Motion GT Corvettes were expensive, and as such, they were only ever built and sold in very small numbers. In this case, it’s the only one left of three GTs built in 1973.

Named the Manta Ray (after Dean Jeffries’ 1963 Mantaray custom, perhaps?), this example is said to have 14 bodywork changes. While they are not specifically listed, they clearly include exposed headlights, a big-block hood, aggressive fender flares all around, chromed Hooker Headers and sidepipes, extended flying buttresses behind the roof pillars, vaned aluminum wheels, an external Monza-style fuel filler, and a tall rear spoiler. In concept, it’s drifting the direction of “Corvette Summer” — but it thankfully stops at early spring.

Modest performance boost

According to the J-code VIN, this car’s original 350-ci engine was the 8.5:1-compression base 190-horse model. That was the lowest output and most common variant for ’73. Although in its metamorphosis to become the Manta Ray, this car’s small block was upgraded to a claimed 425 hp, driving through a stout TH400 transmission.

Other underhood upgrades include an MSD ignition and Accel coil, black-finished carburetor, chrome-plated master cylinder cap and alternator, a shorty air filter with mesh top, and Motion-branded aluminum valve covers.

Equipped with the automatic transmission, power windows and air conditioning (recently serviced), this Manta Ray was clearly intended for comfortable driving to go with its flashy red and black paint and upgraded power. In other words, it’s equal parts show and go.

All the money

The Shadow may have known what lurks in the hearts of men, but I don’t. That’s a weird way of saying that it’s tough to predict what will cause a bidding war at auction. Under normal circumstances, I can imagine a custom ’70s ’Vette struggling to reach $20,000, but in this case the buyer paid five times more for what some might call a tarted-up low-spec ’73 coupe, of which over 25,000 were made. Why? The answer lies in that in-period Motion connection.

There’s a legitimizing factor here with this car because it was sold as a complete custom built by Motion rather than being somebody’s homebuilt creation. It survives as a unique and authentic connection to the 1970s and to the well-known performance tuner. And so in its own way, this car is a minor one-of-one holy grail, and to at least two bidders in the room at Mecum, it was worth over $100k.

With just enough design modifications to make it look like a street-legal race car (the Motion Performance mission), and stopping just short of being silly (like the Monkeemobile or “Corvette Summer” coupe — also a ’73, by the way), the Manta Ray walks a fine line between performance and whimsy. And while those bell bottoms and polyester suits may still be best left in the closet, rare cars like this Motion ’Vette are clearly still strutting in the marketplace. But I still think it was well sold.

(Introductory description courtesy of Mecum Auctions.)

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