Corvette Chronicles: An Experimental Magnesium Corvette Hood

How much information about the project, which eventually became known as Corvette, do you really know? In actuality, it started as an experimental vehicle built from lightweight materials. Various versions were manufactured and eventually, the two-seater as we know it today was ready for its unveiling during the GM Motorama at the Waldorf Astoria Hotel in New York City.

Born of a fiberglass composite, it is no surprise the engineers tasked with creating Corvette would continue on their trek to making the car as light as possible. One such attempt was spearheaded by the knowledgeable minds at Dow Chemical between 1960 and 1961. In the midst of the space race, once exotic materials and techniques became much more common, and manufacturers were at least willing, if not able, to use them on their ground-going rockets as well.

Corvette hood

Today we have carbon-fiber body panels as standard equipment, but in the early-’60s, a lightweight Magnesium hood was straight from the space age.

General Motors had been experimenting with lightweight materials since the late-’30s and ’40s. The benefits of utilizing different materials go way beyond simply making a car faster. Production costs, oxidation resistance, and overall strength can also relegate or eliminate material from consideration. While we all know fiberglass and composite materials make up the bulk of our Corvettes — the current exception being the extent of carbon-fiber that is seeing production in recent years — the constant search for a better, lighter way is not a new one.

As the last few years of the solid-axle era were working their way down the St. Louis Assembly plant, folks at Dow Chemical contacted Chevrolet with the idea of manufacturing car parts out of lightweight Magnesium. Magnesium is found as a natural element and was first discovered in the early-1800s. It has all the desired characteristics of a good candidate for body panels; it is light and durable. Magnesium’s major drawback is it will burn with a very bright fire if it gets hot enough.

Dow recommended building body panels out of lightweight magnesium, stating it could benefit General Motors’ bottom line as well as Corvette’s quarter-mile times. They suggested building the Corvette hood out of Magnesium for the 1960 model, in an experiment that would continue into the 1961 model year run. Dow’s engineers set out by creating three different designs of magnesium hoods to test the feasibility of production, cost, and final fitment for use on production Corvettes.

There were three designs created out of Magnesium: the two-piece hood (left), the one-piece hood (center), and the X-brace hood (right).

According to the Experiment Record, “Three magnesium Corvette hoods, fabricated at Bay City for A. O. Smith Corporation, were assembled and prepared for finishing at Madison. Each hood was of a different design. Because of the difficulty in fitting hand-formed pieces together for bonding and contouring in the car, many compromises in adhesion and assembly were necessary.”

Two-Part Hood

The first attempt listed in the report was a two-piece hood that utilized an outer shell and a sub-structure made from .063-inch Magnesium sheet. The outer shell followed the typical lines of the Corvette, while the under-hood panel carried a “six-pack” appearance. When both panels were mated together, it was determined they were as much as 5/8-inch apart in some areas.

The two pieces could be coerced more into unison, so the engineers added some heat, a few clamps and a plaster mold supplied by A. O. Smith to help the two become one. Some weights were added to the center bracing under-hood to help it better match the outer skin’s curvature. But, after curing in the oven, a dimple was found on the outer surface. To correct this issue, the Corvette hood was re-heated in the oven with the weight concentrated on the dimple. This proved to be ineffective, so the hood was shipped back to a Mr. Pomaville, who “removed the dimple.”

Corvette Hood

The underside of the two-piece hood looked much like a modern Batman’s suit, with its six-pack appearance. Significant modifications were necessary just to get these two pieces to mate together.

Not to be outdone by a dimple, the Dow team tried to mate the two pieces using only steel shot and sand, instead of C-clamps. The idea was to distribute the weight evenly, thereby eliminating the dimple in the process. The dimple again appeared, so the hood was sent to get cut and welded in an attempt to remove some metal. Upon welding, the hood warped so severely, it was scrapped.

A new skin was received and bonded to the reinforcing section, which was still up to 5/8-inch in disagreement. Since the heat was determined to be the issue with the first attempt, it was determined a cold-curing adhesive should be used to hold the two halves together. This alternative method for bonding was found subject to quicker failure under shock or vibration.

The two halves used a bonding agent and a battalion of C-clamps to keep it together until it cured. Even then, fitment was questionable.

To fill in the gaps, Dow employees mixed up a concoction of Vermiculite, Zonolite, Magnesium pellets, and a cold-curing epoxy. It was noted that the hood, once complete, was extremely rigid. But, when fitted to the car, it was found to be “somewhat long.” A. O. Smith reportedly suggested Dow “saw off the front end,” which entailed further modifications.

The resulting modifications weakened the bond at the front of the hood, and when the body man attempted to contour the hood to the car’s shape, it broke loose. Subsequent repairs were done by drilling and filling. The hood was finished, painted black and delivered to Chevrolet. The black, two-piece hood was then modified by Chevrolet to fit a 1961 car by cutting out a portion of the reinforcing section to allow room for the radiator. Chevrolet attempted to repaint it, at which time the previous coatings began to lift. The hood was then stripped and re-painted Fawn Beige and installed on a Corvette “for several weeks” for testing.

The Onesie

As the name implies, the second hood mentioned in the report was a one-piece affair that consisted of .100-inch thick material. Pieces of bent and extruded channels were hand-formed to provide for the necessary hinge, latch, and support brackets.

A lesson learned from the first hood; workers used skip-welding to help minimize heat and warping of this hood. The “skipped” areas were then filled in after the area had sufficient time to cool. It is reported that this worked, and no warping was observed. The hood was reported “not stress-relieved after welding” but was chrome-pickled in the extrusion dip tank and primed. (Editor’s Note: Pickling is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust, or scale from ferrous metals. A solution called pickle liquor, which usually contains acid, is used to remove the surface impurities.)

Corvette hood

The one-piece hood was thicker and used hand-fabricated mounts for the hinges and latches.

Once the hood was delivered to the local Chevrolet garage to be fitted, it was discovered the hood’s contour did not match the car. Then, the body man at the local dealership found out how hard magnesium is to manipulate.

To mate the lines of the hood to those of the car, the body man applied “Black Magic,” an epoxy-like compound which was “plastered on the hood” and then sanded. Scientific experimentation, indeed! Once the hood was finished, it reportedly weighed almost 13 pounds, but no mention of the hood’s original weight is mentioned.

The only Magnesium hood known to exist is the one-piece version. It resides in Mike Yager’s collection at Mid America Motorworks in Effingham, Illinois. Photo: Ed Baumgarten/Mid America Motorworks

After the hood was painted white, it was tested on a Corvette at speeds up to 110 miles per hour. While the design withstood the high-speed highway test, Chevrolet folks contested it did not seem sturdy enough while resting on the single support arm in the up position. After approximately two-months and some 3,000 to 4,000 miles of real-life testing, this hood was returned to Dow for examination. Some cracks were found at the bracket welds and at the end of the rear flange. This is the only hood known to exist today and resides in Mike Yager’s collection at the Mid-America Motorworks facility in Effingham, Illinois.

The X-Brace

The last design, utilized a cross-brace on its underside to give the hood stability. The outer shell consisted of a .091-inch-thick Magnesium sheet. There was a distinctive X-brace that gave the hood its stiffness, while braces that ran across the front and rear underside of the hood were used to attach the hinges and latch mechanisms. The bracing was bonded to the sheet with 3M adhesive and cured at room temperature.

Corvette hood

According to the report, the X-brace hood likely received the most R&D. It is also apparent toward the end of the report that time was short, and so were tempers!

This hood was completed and installed on a 1961 Corvette on December 22nd of that year. It had been designed for a 1960 model. Since A. O. Smith didn’t fit the hood to the car and never tried it on a ’61 until it was completed, the modifications required after the fact are described in the report as “unusual to say the least.”

Major modifications to the bracing were required. The rear brace was cut, lowered 7/16-inch, bonded, and re-riveted using aluminum rivets. The front bracing was moved forward approximately 1/2-inch and then cut to allow room for the radiator.

Official reports are typically void of emotion, but you can’t help but pick up on the frustration when you read, “After repeated assurances by Mr. Edelmann that the hood fitted, it was bonded with 1838 using dental floss as a spacer, cured a day, and delivered to him. The hood was returned shortly, with approximately 20-inches of bond torn loose. Evidently, the hood did not even fit the 1960 car; the X-bracing did not clear and when the hood was closed, the leverage tore loose the adhesive.” We feel their pain, we really do!

Corvette hood

One of the major issues was getting the hoods to fit properly. The report notes how difficult it was to “work the Magnesium” to get it to fit.

The report goes on to list the various repairs and modifications this hood received in an attempt to validate it for use on a Corvette. Everything from the aforementioned dental floss to fiberglass tape was added to sufficiently strengthen the hood. As the rest of the report is read, it is easy to sense the structural integrity of the hood wasn’t the only thing being tested. Further, “we told you so” instances are recorded in the report. The hurriedness of the project comes into play toward the end and as such, questions the repeatability of repairs in the future. This last hood then went on to be fitted on yet another Corvette, upon which there were more interferences found and the hood was modified yet again.

The Bottom Line

As you consider today’s computer-aided design and the fact so much testing can be done through a keyboard, viewing reports such as these helps shed some light on the numerous stages of testing and trials that occurred during the creation of just one component. Today’s Corvettes have throngs of computer files indicating the exact placement of every bolt and nut, but back in the ‘60s, things were definitely different. On the other side of the coin, if you compare the corporate climate between then and now, it appears that not much has changed.

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About the author

Andy Bolig

Andy has been intrigued by mechanical things all of his life and enjoys tinkering with cars of all makes and ages. Finding value in style points, he can appreciate cars of all power and performance levels. Andy is an avid railfan and gets his “high” by flying radio-controlled model airplanes when time permits. He keeps his feet firmly grounded by working on his two street rods and his supercharged C4 Corvette. Whether planes, trains, motorcycles, or automobiles, Andy has immersed himself in a world driven by internal combustion.
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