Lighting the Flame

Working with limited resources, racer Mauri Rose heats up a Chevy passenger-car engine to power the first Corvette

Lighting the Flame 1
May 19, 2016

It’s 1952, and the original Team Corvette is under the gun. Chevrolet’s R&D Department, under the leadership of British suspension expert Maurice Olley, has full responsibility for the design of the underpinnings of the new sports car that carries shop order (SO) 1737. As Olley later told the Society of Automotive Engineers, “On June 2, 1952, Chevrolet engineers were shown a plaster model of a proposed car of 102-inch wheelbase, for which a chassis was required.

“The need was to produce a sports car,” Olley continued, “using components of known reliability, with adequate performance, a comfortable ride and stable handling qualities, in something less than seven months before showing and 12 months before production. There was not much time,” he added, with authentic English understatement.

Though it was Olley’s project, Chevrolet chief engineer Ed Cole was really in charge—as was always the case when an unusual new car was taking shape somewhere within his orbit. “Cole was there in the shop in his shirtsleeves,” recalled one Chevy man, “every night, after his other day’s work was done.”

Sailing under the purposely obfuscatory “Project Opel” code name—a reasonable enough designation, since Chevrolet often designed cars and components for GM’s German subsidiary—a chassis concept for the car rapidly took shape. An Olley sketch dated only 10 days after he was handed the assignment showed the frame and suspension in virtually final form.

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To a degree not recognized at the time, or even since, Cole and Olley created bespoke underpinnings for their sports car—its chassis was anything but warmed-over Chevrolet. They fell short of all that they might have done, especially with respect to the brakes, but then there was precious little time to do it, and none at all for false starts and major changes.

Overseeing the chassis’s physical creation was engineer and racer Mauri Rose, who had been at Allison Engineering in Indianapolis but was in California, contemplating a career wind-down, when contacted by Chevrolet’s Pat Collins. “He said, ‘We’ve got a new chief engineer named Ed Cole,’” Rose later recalled. “‘Would you come back and meet with him?’” He would and did.

Short, wiry, bespectacled and a pipe smoker, Rose was a deceptive figure. Although always employed as an engineer, he had won three Indianapolis 500-mile races, competing “for the fun of it.” Cole knew Rose was just the right man to oversee Project Opel, and awarded him the job.

“There were no drawings,” Rose said of the sports car. “All [Cole] had was an eight-and-a-half-by-11 sketch. He asked me how soon I could start, and I said I’d be back by Labor Day. We did all the work in a loft, not at the Chevrolet factory. We built the whole chassis there.”

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“This was a crash program,” a Chevy engineer added. “They took their sketches right into the build shop and roughed up the chassis in wood and Styrofoam, right off the drawing boards. If it wasn’t right, they tore it down and started over.”

“He was a hard-working, sharp, ‘run to win or bust’ sort of cat,” said Smokey Yunick of Rose, with whom he ram-rodded Chevrolet’s racing program from 1955 to 1957. “If you worked with him and goofed off, or didn’t know what you were doing, you got your ass bit hard constantly. He smoked a pipe, and when he started ‘running hot,’ that pipe would wiggle up and down.

“For a self-taught engineer, he was plenty good,” Yunick continued. “He didn’t have to do physical work. He didn’t have to put in 80 hours a week. He did it because he was a racer first, [and a] Chevy engineer second. If racers were ranked somehow from privates to generals, Mauri would have been a five-star.”

Pat Collins kept in the loop, supporting Rose’s work. Also involved was Maurice Seiberling “Rosey” Rosenberger, an engineer with long experience who shared Cole’s urge to innovate. “When Ed was picking people to get things done,” said Rose, “he picked Rosenberger. He was responsible for the spirit of the job too. He was a doer, not a talker. Whatever we needed, he would help us get it.”

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Their approach often got them in trouble with the union, which held, as Rose said, that “certain engineers weren’t allowed to twist wrenches. The union would go to Rosenberger and [say], ‘Rose is doing this, doing that—stop it.’ Rosenberger said, ‘I’m not going to stop him. I’m doing it myself!’ We got away with murder.”

Deceptively bland and placid in appearance, Rosenberger was a key Cole ally with seven patents to his name. “This man was a smart, hard-working, dedicated team player,” said Yunick. “Rosey was a Chevy man clean through. I bet his shorts had the bowtie all over ‘em. I admired him and tried to adopt his easy-going, unhurried and deliberate method of analysis and solution. No one could work around Rosey and not learn. He was a natural-born teacher.”

One of the team’s biggest challenges was to endow SO 1737 with the kind of oomph under the hood that a sports car required. This was Cole’s specific assignment to Mauri Rose. “He wanted somebody hot to do this engine,” Rose recalled, “not a ‘stick in the mud.’ He wanted somebody high-performance minded to do it. Every morning Cole would come in and ask, ‘How much horsepower have you got today?’

“He was never one for working just during business hours,” Rose continued. “On a Saturday or Sunday, I spent more time with Cole at his home than at the office. We’d look at something. He’d say, ‘You go in on Monday, see so-and-so…show him what you’ve got…and get a cost on it and let me know.’ If he liked it, you’d go to the production group and tell them to do it. He was very informal, very direct, very forceful and very knowledgeable. And a swell person to work for.”

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Rose had an improved basic engine to work with, the new, 1953 version of the large-displacement inline six that had been paired since 1950 with the Powerglide two-speed automatic transmission. Displacing 235.5 cubic inches (3.9 liters), it was in fact a passenger-car edition of a truck engine that Chevy had introduced in 1941.

Although its pushrod-operated overhead valves were a feature that had given Chevy an early advantage over Ford’s flatheads, they were unusually deployed, with the exhaust near vertical and close to the piston top, and the inlet angled and much higher, in a mini-chamber of its own. It was a layout that stalled efforts to make the valves very much larger.

For 1953 the engine was already scheduled to have aluminum pistons—a first in Chevy history—as well as a revised bottom end with full-pressure lubrication for its four main bearings and steel-backed rod-bearing inserts. With its standard 7.5:1 compression ratio, this powerplant delivered 115 hp at 3,600 rpm—not nearly enough for Cole’s sports car. One of the least potent engines in America’s automotive arsenal, it outpowered only the humble base engines of Willys, Nash, Studebaker and the Henry J. But it was a robust basis for Rose’s ministrations.

Fortunately Chevrolet’s Blue Flame Six was by no means an unknown quantity when it came to aftermarket power enhancement. In the hot-rod world, plenty of enthusiasts backed Chevy against Ford in the horsepower sweepstakes, so ample know-how was on the shelf. Two- and three-carburetor manifolds were available from Thickstun, Nicson, Sharp, Edelbrock and Edmunds. Fenton offered both inlet manifolds and dual-exhaust headers, while Frank McGurk specialized in the Chevrolet six and its big sister made by the GMC Truck Division. Special camshafts were on the shelf at Iskenderian and, with roller followers, from Chet Herbert. So Rose didn’t have to start from zero.

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For Project Opel the compression ratio rose to 8.0:1, which called for high-test fuel. Improvements in induction, timing and exhaust were classic avenues to higher horsepower. Mechanical tappets were activated by a new camshaft that gave lift at the valve of 0.405-inch for the inlets and 0.414-inch for the exhausts. Overcoming the cylinder head’s constraints on valve enlargement, these were at the time the highest valve-lift figures in the American industry.

Valve timing became 19.5/44.5 degrees for the 1.875-inch inlet valves, and 59/5 degrees for the 1.5-inch exhausts. An aluminum driven gear on the camshaft replaced the fiber gear that was usually fitted. To permit safe revving to 5,000 rpm, dual springs closed each valve. Exhaust valves were shortened and made of a tougher silichrome-alloy steel.

On the inlet side, some form of horizontal induction was mandatory because downdraft carburetors would have poked through the Corvette’s hood. Rose went all the way to three horizontal Carter YH-2066-S carburetors mounted on a special aluminum manifold. With the throat of each aimed toward a siamesed pair of inlet ports, all three were also connected by a small-diameter surge pipe to even out fuel/air distribution. Cast into the manifold were passages that allowed it to be warmed by exhaust heat, to improve vaporization of the incoming charge. This was thought not strictly necessary at first, but production Corvette sixes did make use of manifold heating.

A double-acting mechanical pump supplied fuel to the single-throat carburetors. “Automatic chokes were tried,” noted Maurice Olley, and in fact they were fitted to the carburetors of the Motorama-show Corvette, “but could not be used because of choke-valve flutter and fast idling. A manual choke [was] therefore fitted.” Large pancake-type air cleaners on the Motorama car were replaced by smaller, bullet-shaped filters in production.

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“We finally got 190 horsepower,” Rose testified. “And Harry Barr said, ‘I know Ed wanted all the horsepower you could get, but the idle isn’t so good and it doesn’t start so well.’ So we gave up the roller camshaft. We ended up with around 150 to 160 horsepower.” The final figure was a respectable 150 hp at a modest 4,200 rpm. Torque, meanwhile, rose from 204 pound-feet at 2,000 rpm to 223 at 2,400. In an apparent attempt to claim parity with Jaguar’s XK120, at the Motorama the public was told that the car had a 160-hp engine. Specific fuel consumption, Olley reported, was no greater than that of the standard Chevrolet.

Two standard Chevrolets were nominated as mules to test the engine and drivetrain on the road, and one can assume they startled more than a few drivers of nominally faster cars. They would have seen a short driver behind the wheel with close-cropped hair, spectacles and a mustache, clenching a pipe between his teeth. Mauri Rose was a hands-on evaluator of what he and his team had wrought.

With the engine installed in Project Opel, the radiator was so low, in relation to the cylinder head, that the cooling system needed a separate header tank. This became a cylindrical tank along the left-hand side of the Motorama car’s rocker cover. In production it was changed in shape and moved to the right-hand side. Here and elsewhere in the installation, said Rose, “Preparations were already made for the V-8 engine to go into the chassis later.”

“A special high-efficiency water pump is fitted low down at the front of the engine block,” wrote Olley in describing the final design. “It is driven at nine-tenths of engine speed, giving a water circulation of 27 gallons per minute at 2,000 rpm. It was originally intended to shroud the fan, which is some distance behind the bottom of the steeply inclined radiator. But cooling tests showed this was unnecessary, as the cooling is far above normal passenger-car standards.” The lower water-pump position, which was originally urged by the stylists, became a standard feature of the production Chevrolet six.

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Rose had time to experiment with several different exhaust-manifold layouts in search of added power. His team tried twin exhaust pipes fed by a single central outlet from the manifold, but this was not too successful. Better results were produced by a split manifold, much like those supplied by Fenton and McGurk, giving separate passages and outlets in a single casting for the gases from the front and rear sets of three cylinders. The manifold’s passages were shaped, Olley said, “to keep the exhaust gases in the throat of each of the two downpipes always whirling in one direction. This was found [to be] essential and picked up some 8 or 10 pound-feet of torque in the mid-speed range.”

Individual pipes and mufflers led back to dual outlets emerging from the rear of the body—another audacious design idea that contributed to the Corvette’s appealing aura of “dream car for the road.” Not by chance did this sports car have twin exhausts for its six-cylinder engine. “Ed said it should have a special sound,” Rose recalled. “‘I want everyone to recognize it when it goes down the street,’ he said. We put a special exhaust system in.”

Straight-through mufflers were tuned to give a robust “motorboat” tone in the best hot-rodding tradition. “A requirement important in the minds of sports-car enthusiasts is that the exhaust should have the right note,” wrote Olley. “They don’t agree what this is. Some prefer ‘foo-blap,’ while others go for ‘foo-gobble.’ It is impossible to please them all. We hope we have achieved a desirable compromise.”

On both the Motorama car and the early production Corvettes, a rocker cover was used that differed from the standard model in placing its oil-filler cap more toward the rear. This was done to provide more clearance and to make it easier to reach, as the hood was hinged at the front, unlike the standard Chevrolet bonnet. In later production both the Corvette and stock Chevys had a newer, trimmer-looking rocker cover with its oil filler at the front.

The electrical system was of a six-volt design, and the battery was at the engine’s right. For positive ignition at and above 5,000 rpm, the breaker cam was modified to give a longer dwell, and a special coil and condenser were specified. An AC 44-5 spark plug was satisfactory for normal driving. For “continuous high-speed operation,” however, Chevy suggested that the colder AC 43-5 COM plug be used.

Because the car’s glass-reinforced plastic (GRP) body provided no shielding, the complete ignition-wiring loom was enclosed by sheet steel shrouding to prevent interference—not only with the car’s radio, but also with radio and TV sets by the roadside. The antenna for the car’s radio was a wire mesh, molded into its rear deck lid, a technique that other firms adopted decades later.

Logic at various levels drove Project Opel’s creators toward the most controversial decision made on the original Corvette: to offer it only with the Powerglide automatic transmission. This married a hydraulic torque converter, to give torque multiplication, with a planetary gearset offering two speeds forward and one backward. The basic engine was the six designed to accompany the Powerglide, so it was easiest to build the “Opel” with that transmission. It was also simplest to equip it with a floor-mounted range control, which was essential anyway because the extra shaft needed by a column shift would have interfered with the rearmost of the three carburetors.

Modifications to the Powerglide for this application included higher hydraulic pressure (to help it handle the engine’s 10-percent-higher torque), doubling the number of bolts driving the torque converter and changing its tailshaft extension to suit the open driveshaft instead of the standard model’s torque tube. The shifter valve was reset to give an automatic upshift from the 1.82:1 low gear at 4,500 rpm under full throttle, the equivalent to 55 to 57 mph.

An automatic kickdown from high to low was possible at any road speed up to 47. Some override of these speeds was possible with the manual shift control, a smallish lever next to the driver’s seat. After evaluating 3.08:1 and 3.37:1 axle ratios, the team chose a shorter 3.55:1 for production. This provided superior acceleration and a top speed of 108 mph at 4,800 rpm on 6.70×15-inch tires.

“The use of an automatic transmission has been criticized,” Olley admitted, “by those who believe that sports-car enthusiasts want nothing but a four-speed [manual] shift. The answer is that the typical sports car enthusiast, like the ‘average man’ or the square root of minus one, is an imaginary quantity. Also, as the sports car appeals to a wider and wider section of the public, the center of gravity of this theoretical individual is shifting from the austerity of the pioneer towards the luxury of modern ideas.” This transition did in fact take place, but about 20 years too late to be of help to the original, Powerglide-equipped Corvette.

Also from Issue 106

  • 1,000-HP Stingray
  • Z-Car Buyer's Guide
  • Superformance Grand Sport vs. Original '63
  • Duntov C3 Turbo
  • GT1 Championship Edition C6
  • DeLorean's Corvette Connection
  • C7.R Chief Mechanics Interviewed
  • Inside GM's Performance and Racing Center
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