Chevy Enthusiast via Hooniverse: The 1975 – 76 Chevy Cosworth Vega


One Vega for the price of two!


Ten years after Chevrolet’s first import fighter was introduced, the fall of 1970 saw another one about to hit the market – and the similarities between the two star-crossed compacts were more than coincidence. History was about to repeat itself, and apparently General Motors had not learned a thing about coming to market with a new platform, new engine, and new technology simultaneously. The car was the 1971 Chevrolet Vega, and it seemed to be progressing down the same path as Chevrolet’s first import fighter, the Corvair.

Both Import fighters were equipped with a brand-new powerplant, not shared with any other line, and with an engine block constructed primarily of an aluminum alloy. The first all-aluminum block, the Vega engine had been developed with the help of Renyolds Aluminum. Its fatal flaw could be traced directly to the absence of cylinder liners: Reynolds engineers had theorized the high-silicon-content alloy would wear at the same rate as steel. Unfortunately, they were out of spec at 40,000 to 50,000 miles, something no one knew when the cars were introduced.

But enough about the standard Vega. It seems that Chevrolet general manager John Z DeLorean (yes, that John DeLorean) pushed his staff to develop a performance version of the Vega for use as a “Halo” variant. This is where Cosworth Engineering came in, led by the dynamic Kieth Duckworth. DeLorean thought the new engine would be a great motor for a full-fledged racing version, so in 1970, both firms went into development. With Vega sales below expectations, GM needed something positive about the car to help prop up sales.

The target was SCCA Production B class, in which the new Vega Twin Cam would compete with the BMW 2002, the Alfa Romeo GTA, and others. Computer models suggest that the Chevy would be competitive because it actually weighed less than most of the competitors, and would have a more powerful engine.

If you want to read more about the Cosworth Vega, and learn why Cosworth licensed the head design to GM, what happens to a Vega block when you try and coax 290 HP from it, find out why DeLorean changed the colors from Silver to Black, and to discover why this Vega was the second most expensive Chevrolet when introduced, you will have to go to the Chevy Enthusiast Site, and follow this link.

0 Comments

  1. I was out of high school for a couple of years when the Cosworth Vega was introduced, and one of my wealthier friends bought one. He drove the crap out of it until the cylinder bores turned banana-shaped. It didn't take long. Then he had to start hauling cases of oil in the trunk to keep the thing running. I remember that most of us were unimpressed by the car.

  2. Excellent article. I've always been a bit mystified by these cars. Cossie engines are often works of art — 290 hp at that time from a 4banger was damn respectable — and the Vega was anything but. It always seems a little like lipstick on a pig.
    However, with the suspension upgrades, the little Vegas were probably pretty tossable on the track and fun to drive. For about a week until the suspension mounts disintegrated.

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    1. Oh, and if you want to read an up and coming Chevy Magazine, pick up a copy at Barnes & Noble.

  4. More history of the Vega and Cossie:http://ateupwithmotor.com/compact-and-economy-car
    To my understanding, for some casting issues with first-year cars, the Vega's linerless bores was not really the major problem with the engine. The problem was that the engine had a tendency to overheat (inadequate radiator capacity, and early cars had no overflow tank), which caused a metallurgical breakdown of the silicon bore surface. If the engine didn't overheat, the bore surface was usually fine. There were various other problems, including bad valve seals that caused excessive oil consumption, that were blamed on the bore surface, somewhat unfairly.

    1. Er, that was supposed to be "except for some casting-issues with the first-year cars, the Vega's linerless bore surface was not…"

  5. Also, I don't think DeLorean had a whole lot to do with the finished Cosworth Vega project. He did initiate it (although it was managed by Lloyd Reuss), but by the time Cosworth dropped out in 1973, DeLorean was long gone — Jim McDonald replaced him as GM of Chevy in the fall of 1972. By the time the Cosworth was first announced to the press, DeLorean had resigned from GM entirely.

    1. They did. The article is conflating several different sets of facts in a way that's a little misleading.
      Except for first-year cars, the A390 bore surface worked pretty well — as long as the engine didn't overheat. Overheating would break down the silicon in the bore surface, allowing the pistons to scuff the cylinder walls. That wouldn't have been a big deal, except that the Vega had inadequate radiator capacity (partly addressed on later cars), and because early cars didn't have an overflow tank for the cooling system, owners who didn't religiously check the coolant levels could run it dry pretty easily. The long-term testing didn't deliberately overheat the engine, so the problem wasn't apparent at the time. (Overheating can often be fatal for aluminum/iron engines because of the different expansion rates, even without linerless bores.) Many Vega engines had problems with valve seals, which would cause high oil consumption that mechanics blamed (incorrectly) on the cylinder bores. People who managed to avoid overheating generally didn't have any problems with them.
      The other half of the story is that during the Cosworth's development, it failed its 50,000-mile EPA durability test at around 40,000 miles — I think that's where Brennan's numbers came from. The engine's failure had nothing to do with the cylinder bores or even the block; the Chevy engineers twiddled the spark timing in an effort to ensure they would pass, and the engine burned a valve. (There was a lot of internal finger pointing over that, with some of the engineers complaining that if they'd just left the timing where it was supposed to be, it would have passed without a problem.)
      This is not to say the Vega engine didn't have a lot of problems, because it did (or that the Vega wasn't built with all the structural integrity of an empty beer can). The author of the article appears to have skimmed over his sources, though, and so the conclusions are a little off.

      1. I agree, the hatchbacks (I've owned two) had all the torsional rigidity of a wet noodle. But then, it was designed in the late '60s, before advanced computers and high strength steel. My '76 GT 5-speed went 218,000 miles (it leaked more oil, through the rope seal and the oil pan gasket than it burned), and the head had never been off. I kept the cooling system in good order, and never let it overheat. It still ran decently when I sold it (for $750, along with a ton of spare and NOS parts), and the last I heard it had been re-sold, to a collector in West Texas.

        1. The lack of structural integrity was in large part because the design was overweight from the start. It was designed by GM Engineering Staff, not by Chevy, and when Chevy got it, they found that a lot of the Engineering Staff's assumptions about weight and cost had been overly optimistic. They found that it was more than 10% over its design weight, so they went on a frantic weight-trimming binge that left it rather tinny. Chevy had to beef up some things because the prototypes kept breaking on the durability course, but that only brought it to the gloomy state of the production models, which was still inadequate.

      2. Makes sense.
        Here's a train of thought: Reynolds Aluminum-> making an engine with Reynolds Aluminum-> making an engine out of Reynolds aluminum foil (Heh. Bad idea.)-> making an engine out of sheet metal-> Crosley CoBra!
        Point is, Crosley seems ripe for a future AUWM article.

  6. The production years were 75 and 76. In 75 they only came in black (sales of 2,000) and in 76 you could get any Vega color (sales of 1,500). By mid 70’s standards they handeled extremely well with almost perfect 50/50 weighting. By 76 they came with a good 5sp, combined with the positraction for even better driving.

  7. I *so* remember these ads. Dad was in the market for a small car, and I had just discovered what Cosworth meant.
    In retrospect, the Mustang II that he got likely served the family much better than this would have.

  8. There is a dealership near me that has a Cossie out front that looks really nice from the street. I've been very good about not stopping to take a closer look, and see how much they want for it. I very much want a Cosworth Vega, but should probably get something a bit more practical as a daily driver for my next automotive purchase.

  9. They would have made it for the 1974 model year, except that during the emissions system durability testing, an engine burned an exhaust valve. That delayed the project for a year.

  10. I've owned two regular Vegas (a '75 base hatchback and a '76 GT hatchback), and I hope to own a Cosworth someday.

  11. I have a 1975 chevy vega which was bought brand new. It has only 76 thousand kilometers and now rest in my garage. Every part is original with its original paint. Hardly any rust. I would like to sell it as I am retired now. If there is any vega enthusiast out there, send me a note.

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