The Chevrolet Cosworth Vega is a subcompact four-passenger automobile produced by the Chevrolet division of General Motors for the 1975–'76 model years. The Cosworth Twin-Cam is a limited production, performance version of the Chevrolet Vega. Its purpose was to "create excitement for the entire Vega line." The production version of the Cosworth Vega twin-cam engine was developed by Chevrolet with the cylinder head design by Cosworth Engineering in England. The vehicle was introduced to the public at the Chicago Auto Show in February 1975. The all-aluminum 122 cu in inline-four engines were hand-built at GM's Tonawanda engine plant — each signed by the engine builder. "Cosworth. One Vega for the price of two" was only $900 less than the 1975 Corvette, Chevrolet's most expensive car. 5,000 engines were built, but only 3,508 cars were produced in 18 months.
In March, 1970 DeLorean sent engine designer Calvin Wade, a 25-year veteran of Chevrolet performance wars, to England in search of the cylinder head technology that would pep up the Vega's engine demeanor for the street. It would take some new technology — fuel injection to control emissions without power loss — and far stouter internal parts to work with the existing block and the Cosworth head. By the Summer of 1970, DeLorean authorized Wade to build the prototype for what would become the Cosworth Vega. But the budget was meager and stout resistance from managers between Wade and DeLorean resulted in low priority for the project. On the positive side, no one could kill the idea once it received approval from John Z.
Prototype parts were in and assembled June, 1971. The Cosworth Vega engine (street version) came to life for the first time. Breathing through a pair of Holley-Weber two-barrel carburetors, the Cosworth quickly turned in a peak of 170 hp. By Easter, 1972 a key break for the Cosworth engine came when several advanced Vega creations were offered to GM President Ed Cole for a drive. A base Vega was on hand for reference to an all-aluminum small-block V8 and the Bendix-injected Cosworth. Ed Cole loved the Cosworth concept and pledged his support in the Engineering Policy Group, which would have to approve DeLorean's request to initiate production. DeLorean's first ride came a few months later. His approval for development — aimed at U.S. Environmental Protection Agency (EPA) certification swiftly followed. Cal Wade began a development program with 12 cars to accumulate emissions certification mileage and prove the engine in a variety of circumstances including high altitudes and hot and cold climates. At the GM desert proving ground, the car could reach 122 mph.
In April, 1973 the design was frozen and two cars were built for the mileage accumulation necessary for EPA emission certification. The press was keyed into the program and a pilot car was the center of attention in the August 1973 Car and Driver, alerting the public to an upcoming 140-hp Cosworth Vega. But what the engine needed was dyno-time, new cam profiles to trade in a little high-end punch for a lot more muscle in the low end and a tubing header to replace the undesirable cast iron exhaust manifold. It meant a much higher priority for the project: more engineering manpower, more money — and also more delay. A chance for a major engineering coup by Chevrolet was clearly within reach if it could get a certified race engine into production. Everyone was watching: Chevy dealers were accepting huge deposits for an early delivery.
Once again the design was frozen in January, 1974. A stainless steel header was specified, which helped horsepower from 2,000 rpm up to the 7,000 rpm redline. Camshaft lift and duration were eased back and throttle area sized down to reshape the torque curve to a street-oriented curve that peaked at 5,200 rpm. Willam Large, project coordinator for several months, built two durability cars and sent them off and running.
By April 1974, emissions performance for the first 40,000 miles showed the Cosworth Vega to have a truly "clean" engine. But then hydrocarbon curves on the first car shot upward at a precipitous rate, far exceeding the allowable 3.0 grams per mile. Disassembly reveled burned exhaust valves. For certification of the Cosworth Vega, five months of durability miles would have to be reaccumulated. Chevrolet argued in vain with the EPA to allow averaging between the two cars. A new round of development was begun, this time to improve emissions durability and also to ready the engine for more stringent 1975 standards. The fuel injection was redesigned for better air distribution. High-energy electronic ignition was added along with the mandatory catalytic converter. A Pulse Air system was added. Functionally, Pulse Air is the same as an air pump but without the pump's six-hp loss. The larger version catalytic converter also prevented a power loss. More advanced timing and the lead-free fuel required with the converter would cancel any likelihood of exhaust-valve failure.
One of Chevrolet's criterion is that all engine designs live for 200 hours at full load. The Cosworth Vega endured the punishment for over 500 hours. For a clutch burst test, Cale Wade bravely buzzed the engine up to 9,400 rpm under its own power. Both the clutch and the engine lived. Three cars began mileage accumulation once again in September 1974 - in three different configurations to insure passage.
By January, 1975 mileage accumulation was completed with no failures. One configuration stayed within 1975 California limits, making the Cosworth Vega the only GM car certified for all 50 states. All cars came close to passing the proposed 1977 Federal standards. On March 14, 1975 the EPA issued Chevrolet an emissions certificate allowing sale of 1975 Cosworth Vegas. Production was begun immediately to fill the backlog of orders. Engine production rate was 30 per day with hand assembly teams two or three workers per engine in the Tonawanda, New York engine plant's "clean room", a special facility originally devised for the ZL-1 all-aluminum 427 cubic inch V8. At the Vega's Lordstown Assembly plant, the Cosworth rate was 1.6 cars per hour.
Cosworth Vega 0001, the original Chicago Auto Show vehicle, complete with its special clear Plexiglas hood is part of the GM Heritage Collection.
In a hand-written August 1969 memo, John DeLorean, then Chevrolet's general manager and vice-president of General Motors suggested Jim Musser, Vega project leader to contact Cosworth Engineering racing experts in England to see if they’d be interested in transforming Chevy’s new aluminum-block into a 300-hp racing engine.
Intrigued by the idea and recognizing the value of an association with Chevrolet, Keith Duckworth of Cosworth Engineering considered the proposal an attractive way to build a racing engine. He promptly visited the States to examine the new Vega block closely. Impressed by its sound structural concepts and logical lines of stress from top to bottom, he was overheard to say, “You couldn’t easily see where it was likely to break first.” Duckworth decided that Cosworth was interested, and a dialog with Chevrolet's engineers began in 1969.
The Cosworth racing engine based upon the Vega aluminum block was known internally at Cosworth Engineering as Project EA. The EA engine produced a reported 260 hp. Installed in Chevron and Lola chassis, it proved the fastest in the 2-liter class in its first outings. During the year that followed, Cosworth of England experienced repeated catastrophic failures of the engine blocks—they had an unhealthy propensity to split horizontally below the cylinder bores. Chevrolet later offered heavy duty blocks but by then Cosworth had bowed out of the program.
Chevrolet pursued a diverging path toward a streetable version of the twin cam cylinder head design, seeking a reliable engine that developed lots of power. Lloyd Reuss, then Assistant Chief Engineer at Chevrolet, decided that a streetable version of the Cosworth engine would be the hot ticket to improving the Vega’s image and Chevrolet’s sporting image as well.
The ZO9 Cosworth Vega is a direct derivative of the EA racing engine. Although it has been widely thought of by the general public as a souped up Vega engine, it is in truth a de-tuned EA racing engine. It lacks the EA's dry sump lubricating system (neither necessary nor desirable for passenger car application), has a lower compression ratio and different valve timing and uses Bendix electronic fuel injection in place of the Lucas mechanical injection, but bore, stroke and valve sizes are identical. The Bendix injection is actually more sophisticated than the Lucas since it has to cope with a wider range of operating conditions as well as emission controls.
All 2,061 1975 Cosworth Vegas were finished in black acrylic lacquer with gold "Cosworth Twin Cam" lettering on the front fenders and rear cove panel and gold pinstripping on hood bulge, body sides, wheel openings, and rear cove. The black exterior color wasn't available on lesser Vegas until mid-1976. The black custom interior with perforated vinyl seat trim (RPO ZJ1) was standard; black cloth seat inserts were available at an additional charge of $50. Approximately 16 percent were equipped with white vinyl interiors. Included with all interiors is a gold engine-turned dash bezel and gold-plated dash plaque with build sequence number, a specific 8,000 rpm tachometer, and a Cosworth Twin-Cam Vega steering wheel emblem.
At $5,916 it cost double a normal hatchback and $892 less than a Corvette. The Cosworth package includes a 'torque arm' rear suspension which provides optimum rear axle power control. This unit compares to the assembly used on the Chevy Monza 2+2. The Monza 2+2 axle is also used and provides a 3.73:1 gear ratio from a 7.5 inch ring gear. No other gear ratios were available, but a limited slip differential was optional. Included are Vega GT springs, shocks, and stabilizer bars (the rear bar larger than the GT's), exclusive BR70-13 BSW radial tires on British-made 6 inch, gold-painted cast aluminum wheels with Chevy center caps, black-finished wiper arms, H.D. radiator and provisions for “Fast Steer” option. This was the first use of electronic fuel injection on a Chevrolet passenger car. Air conditioning was not offered on the Cosworth Vega. Power steering and power brakes were also not offered. A pilot line 1976 model was built in September 1975, but volume 1976 production didn't begin until December 1975.
1976 models at $6,066 received a facelift including a wider grill and tri-color tail lamps and extensive body anti-rust improvements including galvanized steel fenders and rocker panels. Larger rear drum brakes shared with the heavier Monza were fitted. A new Borg-Warner five-speed manual overdrive transmission with 4.10 axle was optional in addition to the std. Saginaw four-speed manual with 3.73 axle. The exhaust system featured a single outlet tailpipe as opposed to the dual outlet pipe on the 1975. The seat trim changed to a grained vinyl and the optional cloth trim seat inserts was changed to a "houndstooth" type, named sport-cloth, for an additional $18 charge. In January, a "Sky-Roof" with tinted reflectorized sliding glass and 8-track tape player options were added.
In February, eight of the Vega's fourteen 1976 exterior colors were added — Antique White, Dark Blue Metallic, Firethorn Metallic, Mahogany Metallic, Dark Green Metallic, Buckskin, Medium Saddle Metallic, and Medium Orange, and two additional interior colors were added — Firethorn, and Buckskin. Still, only 1,447 were built. Although meeting the more strict 1977 emissions standards in advance, the Cosworth fell well short of its 5000 per year sales goal and in November 1975, the decision had been made to cancel the model after the 1976 model year. Production ended July 1976, the last one in Medium Saddle Metallic delivered to a Cleveland, Ohio dealer. 3,508 total were built—190,321 Vega hatchback coupes were produced in the same 18 month time period from March 1975 through July 1976.
122 CID DOHC
The Cosworth Vega Twin-Cam engine is a 122 CID (121.7 cu in) 1,994 cc inline-4 featuring a die cast aluminum alloy cylinder block and a Type 356 aluminum alloy, 16-valve cylinder head with double overhead camshafts (DOHC) designed in conjunction with Cosworth Engineering of England. The camshafts are held in a removable cam-carrier which also serves as a guide for the valve lifters. Each camshaft is supported by five bearings and is turned by individual cam gears on the front end. The two overhead camshafts are driven, along with the water pump and fan, by a fiberglass cord reinforced neoprene rubber belt, much like the Vega 140 cubic inch engine. Below the cam carrier is a 16-valve cylinder head constructed of an aluminum alloy using sintered iron valve seats. Sturdy forged aluminum pistons and heat-treated forged steel crankshaft and connecting rods reveal racing ancestry; assure high performance durability. The engine features a stainless steel exhaust header and electronic fuel injection (EFI) – a Bendix system with pulse-time manifold injection, four injector valves, an electronic control unit (ECU), five independent sensors and two fuel pumps. Each engine was hand-built and includes a cam cover sticker with the engine builder's signature.
The Cosworth Vega engine is some 60 pounds lighter and presents a far handsomer spectacle than the odd looking SOHC Vega engine. The engine develops its maximum power at 5,600 rpm and is redlined at 6,500 rpm where the SOHC Vega engine peaks at 4,400 rpm and all is done at 5,000 rpm. Final ratings are 110 hp at 5,600 rpm, 107 foot pounds of torque at 4,800 rpm. With only 3,508 of the 5,000 engines used, GM disassembled about 500; the remaining engines were scrapped for a writeoff of $10k each.
"The Cosworth Vega 16-valve four cylinder is the most sophisticated engine Detroit ever made." - Car and Driver, October 1975
Aluminum engine block
GM Research Labs had been working on a sleeveless aluminum block since the late '50s. The incentive was cost. Engineering out the four-cylinder's block liners would save $8 — a substantial amount of money at the time. Reynolds Metal Co. developed an alloy called A-390, composed of 77 percent aluminum, 17 percent silicon, 4 percent copper, 1 percent iron, and traces of phosphorus, zinc, manganese, and titanium. The A-390 alloy was suitable for faster production diecasting which made the Vega block less expensive to manufacture than other aluminum engines. Sealed Power Corp. developed special chrome-plated piston rings for the engine that were blunted to prevent scuffing. Basic work had been done under Eudell Jackobson of GM engineering, not at Chevrolet. Subsequently, Chevrolet was given job of putting the ohc sleeveless, aluminum block into production.
The Vega engine block was cast in Massena, New York - at the same factory that had produced the Corvair engine. Molten aluminum was transported from Reynolds and Alcoa reduction plants to the foundry, inside thermos tank trucks. The block was cast using the Accurad process. The casting process provided a uniform distribution of fine primary silicon particles approximately 0.001 inches in size. Pure silicon provides a hard scuff and wear resistant surface, having a rating of 7 on the mohs scale of hardness, the same as quartz, as compared to diamond which is 10. The blocks were aged 8 hours at 450 °F to achieve dimensional stability. The technical breakthroughs of the block lay in the precision die-casting method used to produce it, and in the silicon alloying which provided a compatible bore surface without liners. Before being shipped to Tonawanda, the blocks were inpregnated with sodium silicate, where they were machined through the outer skin. From Massena, the cast engine blocks were shipped as raw castings to Chevy's engine plant in Tonawanda, New York. Here they underwent the messy etch and machining operations. The cylinder bores were rough and finish-honed conventionally to a 7-microinch finish then etched by a new (then) electro-chemical process. The etching removed approximately 0.00015-inch of aluminum leaving the pure silicon particles prominent to form the bore surface.
With a machined weight of 36 pounds, the block weighs 51 pounds less than the cast-iron block in the Chevy II 153 CID inline-4. Plating the piston skirts was necessary to put a hard iron skirt surface opposite the silicon of the block to prevent scuffing. The plating was a four layer electo-plating process. The first plate was a flash of zinc followed by a very thin flash of copper. The third and primary coating was hard iron, 0.0007-inch thick. The final layer was a flash of tin. The zinc and copper were necessary to adhere the iron while the tin prevented corrosion before assembly of the piston into the engine. Piston plating was done on a 46 operation automatic line. From Tonawanda, the engines went to the Chevrolet assembly plant in Lordstown, Ohio.
Eudell Jackobson of GM engineering pointed out one of the early problems with unexplained scuffing and discovered excessive pressure on the bore hones was causing the silicon to crack. He said:"...We were trying to put a product into production and learning the technology simultaneously. And the pressure becomes very, very great when that happens. The hone-pressure problem was solved before engines actually went out the door, affecting only pre-production engines.
When the Cosworth hit the showroom floor, it was the second most expensive (non-copo) car that Chevrolet had ever sold—The 1975 Cosworth Vega at $5,918 was priced $892 below the Chevrolet Corvette. "Cosworth. One Vega for the price of two" as it was advertised, was priced out of the market, and fell well short of its projected sales goal.
|1975-76 Cosworth Vega|
Current market value is 700% of original MSRP for the best 1975-'76 examples.
1975-1976 Chevrolet Vega Cosworth
2dr Hatchback Coupe 4-cyl. 122cid/110hp EFI
1 Concours $42,500
2 Excellent $26,000
3 Good $12,500
4 Fair $7,200
Average Value $12,500
note: Hagerty Valuation values as of May 2021
Condition #1 vehicles are the best in the world. The visual image is of the best vehicle, in the right colors, driving onto the lawn at the finest concours. Perfectly clean, the vehicle has been groomed down to the tire treads. Painted and chromed surfaces are mirror-like. Dust and dirt are banned, and materials used are correct and superbly fitted. The one word description for #1 vehicles is "concours."
Condition #2 vehicles could win a local or regional show. They can be former #1 vehicles that have been driven or have aged. Seasoned observers will have to look closely for flaws, but will be able to find some not seen by the general public. The paint, chrome, glass and finishes will all appear as excellent. No excessive smoke will be seen on startup, no unusual noises will emanate from the engine. The vehicle will drive as a new vehicle of its era would. The one word description for #2 vehicles is "excellent."
Condition #3 vehicles could possess some, but not all of the issues of a #4 vehicle, but they will be balanced by other factors such as a fresh paint job or a new, correct interior where applicable. #3 vehicles drive and run well, but might have some incorrect parts. These vehicles are not used for daily transportation but are ready for a long tour without excuses, and the casual passerby will not find any visual flaws. "Good" is the one word description of a #3 vehicle.
Condition #4 vehicles are daily drivers, with flaws visible to the naked eye. The chrome might have pitting or scratches, the windshield might be chipped. Paintwork is imperfect, and perhaps the body has a minor dent. Split seams or a cracked dash, where applicable, might be present. No major parts are missing, but the wheels could differ from the originals, or other non- stock additions might be present. A #4 vehicle can also be a deteriorated restoration. "Fair" is the one word that describes a #4 vehicle.
Car and Driver October 1975, "How to Hatch an Engine" editor Don Sherman said, "The Cosworth Vega 16-valve four cylinder is the most sophisticated engine Detroit ever made. Yet the men who created this mechanical work of art and the public that patiently waited its arrival must regard the car in a different light. They will not soon forget the record gestation period: five long years from concept to customer." "So with this engine, wrapped in a glistening black jewel of a gift to car freaks, an era has passed." "Cal Wade's patience is shot, but his race-bred engine is in production. Just don't expect such a thing to ever happen again."
"To commemorate this final act of the performance age, here is the drama as it happened:
March 1970: John Z DeLorean sent engine designer Calvin Wade to England in search of cylinder-head technology that would pep up the Vega engine's demeanor." "Duckworth— the "worth" of Cosworth Engineering assigned his own engineer Mike Hall and Wade set out to design the top half of the Cosworth Vega using the standard Formula One layout of a head with four valves per cylinder operated by double overhead cams." "Flying back to the U.S. after one of his 13 trips to England Carl Wade's mind drifted over thoughts of a Cosworth for Everyman; the race engine tamed for street use."
Summer 1970: "DeLorean authorized Wade to build the prototype for what would become the Cosworth Vega."
Spring 1971: "The Chevrolet Vega was introduced to enthusiastic notices from the press, but there is a tinge of reluctance to the engine's "advanced technology," fearful of aluminum's somewhat shaky durability record." "DeLorean knew the Vega's durability image needed improvement. Racing success with the Cosworth engines might do part of the job, but DeLorean felt the public needed a strong image car to lust after..." There was also a frontier to be won with electronic fuel injection in the United States, one DeLorean longed to add to his marketing combat record." "Carl Wade brought Bendix to his bosses, including an eager DeLorean, and successfully sold it. This allowed Chevrolet engineers to get their feet wet EFI where cost was not a major concern."
June 1971: "Prototype parts were in and assembled. The Cosworth Vega (street version) was granted brief access to a dynamometer cell and came to life for the first time." "Breathing through a pair of Holly-Weber two barrel carburetors, the Cosworth quickly turned in a peak of 170 hp."
Easter 1972: "Cal Wade began a development program with 12 cars to accumulate emissions certification mileage and prove the engine in a variety of circumstances including high altitudes and hot and cold climates. At the proving ground, the car could reach 122 mph."
April 1973: "The design was frozen and two cars were built for the mileage accumulation necessary for EPA emissions certification." "Five pilot-production Cosworth Vegas were built." "The press was keyed in to the program and a pilot car was the center of attention in the August 1973 Car and Driver, alerting the public to an upcoming 140-hp Cosworth Vega."
January 1974: "Once again, the design was frozen. A stainless steel header was specified, which helped horsepower from 2000 rpm up to the 7000-rpm redline."
April 1974: Two durability cars were off and running. Emissions performance for the first 40,000 miles showed the Cosworth Vega to have a truly "clean" engine. Then hydrocarbon curves on the first car shot upward far exceeding the the allowable 3.0 grams per mile. Disassembly revealed burned exhaust valves. Chevrolet argued in vain with the EPA to allow averaging between the two cars." "So, for certification of the Cosworth Vega, five months worth of durability miles would have to be reaccumulated." "No one wanted failure the second time around so every possible step was taken to make the Cosworth both a low polluter and a bulletproof exercise in durability. One Chevrolet criterion is that all engine designs live for 200 hours at full load, cycled between the torque peak and horsepower peak. The Cosworth Vega endured this type of punishment for over 500 hours. In fact, it is possibly the most durable high-performance engine ever built."
September 1974: Three cars begin mileage accumulation once again-in three different configurations to insure passage."
January 1975: Mileage accumulation was completed with no failures. One configuration stayed within 1975 California limits, making the Cosworth Vega the only GM car certified for all 50 states."
March 1975: "The EPA issued Chevrolet an emissions certificate allowing sale of 1975 Cosworth Vegas." "Engine production is 30 per day (using a rare personal touch: hand assembly teams of two or three workers per engine).
And Now That It's Here, How Does It Run? "Don Sherman clocked a respectable 0-60 in 8.7 seconds and the quarter mile in 17.6 at 80.1 mph. He observed a top speed of 107 mph. Sherman wrote, "The reason the Cosworth Vega isn't neck-snapping quick is simple: it has a poor power-to-weight ratio. When the first hints of the Cosworth were heard, 140-hp numbers were bandied about; but in the harsh reality of 1975, the dyno says 111." "Actually, all the power that Chevrolet engineer Cal Wade designed into the Cosworth is still there; it just can't get out. Chevrolet is very conscientious about noise standards (they say that's what killed the Z/28), and the exhaust system that makes the Cosworth Vega legal eats up 21 hp." "Right now, the best part of the Cosworth Vega from the backside of the steering wheel isn't even the engine..."The outstanding feature of the Cosworth Vega is its excellent balance..Roll-stiffness distribution is ideal, with little understeer entering a turn, and just the right amount of drift from the tail as you put your foot down to exit. Braking is sure, and the high efforts involved with 1976's semmi-metallic pads and larger brakes give you the feel you need to out-deep all comers." "Through the woods or down a mountain, the Cosworth is a feisty aggressor willing, if not altogether able to take on the world's best GT cars."
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