Tested: 1974 Chevrolet Cosworth Twin Cam Vega (2024)

From the January 1974 issue of Car and Driver.

The tach needle freezes at 1600 rpm when you let the Cos­worth Twin Cam Vega idle. The engine is calm and polite at that speed; a faint tinkling of exhaust gases rattling through a tubing header is the only hint at the vibrant spirit bolted under the obsidian hood.

But toe into the throttle and you strip off that mild-man­nered cover. Definitely. Response is instantaneous. The en­gine's eagerness almost anticipates your own. Revs escalate with the speed of the electrons which regulate the fuel-air mixture. Step out of the clutch and you move off the mark with authority, hurtled into motion by a very low first gear and an instant leg up on the torque curve. Second is a big step away . . . so you run up to the red. The tach needle hurtles to touch seven thousand before you pull the lever, but the Cosworth Twin Cam doesn't falter. It is a soprano with the rare talent to sing its high-octave rpm song indefinitely.

Chevrolet Motor Division would have it no other way. The Cosworth Twin Cam Vega is its latest Image Car, temporarily upstaging even the Corvette. Chevy, late into the small-car market with the Vega, has something to prove. And they're doing it with a race motor tuned for the street and harnessed to an American subcompact. Double overhead cams, four valves per cylinder, a linerless aluminum block and head, electronic fuel injection, electronic ignition—all held together with aircraft-grade fasteners. Enough science to fill an engi­neering journal the size of the Manhattan phone book. More than enough mechanical trickery to make an enthusiast's, even a purist's, heart pound with anticipation.

It is all a way of generating excitement about small cars which ultimately (Chevy hopes) will translate into sales. And as an image car, the Cosworth Vega must be as faultless as a vice-presidential candidate. Particularly when the opposition party is polishing and grooming something like the Mustang II as a contender for the top spot. So before Twin Cam Number 0001 is delivered to its owner next month, it will be closer to perfection than any machine ever released from the laborato­ries of Chevrolet Engineering. In this case, that has meant a blank-check approach—whatever premium materials needed to do the job have been specified. The whimperings from cost accountants have been virtually ignored.

Chevrolet management's goal is one more assembly plant pumping out cars at full-rated capacity. If the check-authoriz­ers have group cardiac arrests in reaching this goal . . . so be it. Camaro, Nova, and Corvette factories have made it, so they get no adrenaline fix this year. But the Vega trailed the Pinto in sales during 1973, and the new Mustang II could take another stab at Chevrolet small car volume. So management has approved an image fortifier, the Cosworth Twin Cam Vega, to rub shoulders with normal Vegas and hopefully drive the subcompact assembly plants toward a few days of overtime.

The motives may seem coldly aimed at quarterly dividends, but you can't argue with energy expended to entice the enthusiast. It is indeed rare treatment for one, probably unprofitable, 5000-unit niche of the market to receive the fruits of a million-dollar development program. Part of that expense has been in final refinements necessary to bring the car's image up to the required sparkle. Initially, the Cosworth Vega pro­gram was rushing headlong toward an end that would have been a vivid disappointment. Though the specs have always looked good, the first prototypes had the makings of a rip-off which would have embarrassed a copywriter in the height of the super car market. Since we drove early versions (C/D, August 1973), that has all been changed. Unfortunately, it will delay the earliest possible sale of the Cosworth Twin Cam until February.

The engine's torque curve needed and received the most attention. Initially, it was as flat as the Bonneville salt, the way any racer would develop his motor for the track. Unfortunate­ly, that approach left the Cosworth Vega a spasmodic lurcher for the street. The low and mid-range engine performance was—to be charitable—soft . . . you needed at least five grand on the tach before traffic began to shrink in your mirror. And even though the wide-ratio four-speed transmission helped get you into the high-energy range quickly, the spacing was so wide that no one would have been able to keep the car from tumbling off the power curve between third and fourth. Chev­rolet wisely decided help was required.

The engineers went back to their dynamometers to bolster the torque curve. The wild cam timing was the first area of attention. Duration and lift were shaved back to fortify the low-speed range. Though this clipped a lot of power off the big end, a new exhaust header was developed to recoup part of the loss. The original manifold was a free-flowing iron casting making no use of exhaust scavenging principles to enhance the torque curve. Now, waste gases are carefully guided through stainless steel tubing joined in such a way that there are tuning benefits from 3500 to 7000 rpm.

The cam timing and header changes have reshaped the torque curve substantially. In earlier versions it was a straight line through 105 pound-feet. Now the curve has a hump, peaking at 5200 rpm with 116 pound-feet of torque. And the horsepower peak is actually lower, with 130 hp (net) at 6200 rpm, compared with 140 hp at 7000 rpm from the early versions. Even so, quarter­-mile acceleration has vastly improved. The current test car's 16.2-second elapsed time and 85.0-mph trap speed betters the early acceleration runs by 0.6 second and 2.3 mph.

On the street, you no longer have to keep the Twin Cam at a whir to move out smartly. Response at 3500 rpm is strong enough to use fourth gear for passing without a long wait for the surge that used to be hiding at five grand. Around town you can ignore the gearbox and still do well. Pintos and Opels drop behind in an instant. Mazdas, V-6 Capris, and 240Zs are a little tougher, but fair game. And if you are willing to stir the shifter, BMW 2002 tiis and Alfa GTVs are yours for the conquering. In fact, the only four-passenger coupes faster than a Cosworth Vega have a Detroit V-8 under the hood.

To match that straight-line brawn, the Twin Cam Vega has what it takes to prevent embarrassment when the road begins to twist. With the new optional 16:1 steering gear, you won't have to move your hands on the wheel except in the tightest of turns. And the suspension is the eminently capable all-coil spring layout from the Vega GT. Spring rates are iden­tical to the less forceful version (this year), with the coils mod­ified to support the extra weight of 5-mph front and rear bumpers. That amounts to 240 pounds over a pre-bumper era 1972 Vega GT, with about 70 pounds of weight saved through the use of forged aluminum face bars. About 40 pounds of weight is eliminated with the all-aluminum Twin Cam engine, so weight distribution is somewhat better than a standard Vega GT. Understeer is still present, but the engine has plenty of torque to drift the rear end out during cornering.

The only serious flaw in handling aris­es from the Vega's four-link, coil spring rear suspension. The Vega has always suf­fered from squat under acceleration and axle tramp during braking because the rear suspension control links are too short. The problem is exacerbated with additional power from the Cosworth en­gine. To diminish the likelihood of power hop, Chevrolet fits Cosworth Vegas with a steel cable to limit the angle between the rear axle and the lower control arm on each side. When the rear axle bot­toms against its rubber jounce bumpers, all slack is out the the cables, so they effectively snub axle windup. It is a crude, but effective, approach. The shortcoming of such a system is the harshness it evokes. On a hard upshift, for instance, the restraints come into play with a bang that sounds like a grenade going off in the trunk. The same harshness also limits cornering power over rough or wavy surfaces for more in­volved reasons. First of all, the BR70 steel-belted radial tires allow more body roll than their bias-belted predecessors. During hard cornering, the outside rear wheel is very close to the limit of sus­pension travel. As soon as a bump demands more deflection, the cure-all ca­ble comes into play to tighten things up. That sudden increase in suspension rate overloads, then temporarily erases, the outside rear tire's traction. The effect is a jerky oversteering response as you corner quickly through the bumps. (The problem is no surprise to Chevrolet engi­neers. They have a solution; un­fortunately it won't see the light of pro­duction until the 1975 model year.)

There is but one other compound flaw still apparent in the production version of the Cosworth Vega. Its transmission ra­tios are ill-suited for much but gymkhana duty, and you can't smooth out down­shifts by heel-and-toe control of the brake and throttle. The latter is a result of Fisher Body Division's reluctance to reshape the Vega's floor pan to allow a new throttle pivot location. You'll have to do it yourself. On the other hand, the transmission ratios are not going to be corrected by sawed-up 2x4s and silver tape. All ratios are shared with the stan­dard Vega four-speed except first, which was lowered from 3.11 to 3.50:1, allowing the smaller twin-cam engine to idle away from stoplights without a quiv­er. The spread between first, second, and third remains quite manageable, but there is a crevass between third and fourth that is impossible for the 2.0-liter engine to bridge. A shift at the redline (7000 rpm) in third drops you to 4200 rpm in fourth, so acceleration to the top speed of 110 mph takes much longer than it should. The obvious answer is a five-speed transmission, and that too will be part of the 1975 model year.

For 1974, you'll have to be content with the raciest engine ever to slide be­neath the hood of an American produc­tion car. Under that crackle-black valve cover lies the technology currently fa­vored for Formula One racing. Very sub­tle indeed are the differences between the Cosworth Vega cylinder head and that of the Cosworth Ford-DFV three-li­ter VS used in Formula One. The latter has racked up an impressive 66 wins out of the last 83 World Driving Champion­ship races. The Cosworth Vega engine will use this racing technology to achieve high performance on the street at low fuel and emissions penalties.

Unfortunately, there will be but an elite few that will taste the rare and exclusive virtues of a racing engine finely honed to fit the needs of a compact American GT coupe. A natural part of the appeal is the exclusivity. Chevrolet engineers have sold management on 5000 cars, but a strong demand could raise that number appreciably. And other GM divisions (Pontiac most overtly) are eyeing the en­gine. It will certainly be available as a service part with a host of heavy duty parts for "non-highway" (i.e. racing) use.

Right now there is a problem deter­mining who will receive the first editions with consecutively numbered dash plaques. There will be less than one for each of Chevrolet's 6000 dealers. The fast-buck outlets will be effectively elimi­nated with the requirement that they buy an expensive service instrument neces­sary to check out the Cosworth Vega's electronic fuel injection system. In any case, many are already holding deposits . . . and there are rumors that some dealers will attempt to auction their allot­ment of cars at prices well above the sticker. Chevrolet has not yet an­nounced the tariff, but the final legiti­mate asking price could well be enough to scare off those frail of bank account. If price is no problem, we suggest you quickly grab a spot in the line.