Chevrolet Corvette

Mystery FactorsTop-speed figures have an aura of imperious finality to them; such, however, is not the case. Sure enough, each of our 16 cars logged the precise speeds shown in this article-on the day and at the place we tested them. But just as a world-class sprinter can't hit his personal best every time out of the starting blocks, so too, minor variations affect the top-speed performance of automobiles.

The venue is a critical factor: It must be flat for the sake of accuracy (though downhill is more exciting). It also needs to have a reasonable amount of grip; pavement is better than the Bonneville Salt Flats or a dry lake, because even a little wheelspin can sap a few mph off of top speed. Air density (determined by altitude and temperature) further skews the results. Though it takes less power to push the car through thinner air, that same thin air results in less power developed by the engine. With the help of intercooling, it's possible for some turbo cars to develop their full rated power at altitude, which means that the higher/hotter you go, the faster the car gets.

Wind has an equally large effect on top speed. Due to the way aerodynamic drag rises with speed, a headwind is much more detrimental than a like-sized tailwind is helpful. That's why simply averaging runs in both directions won't give you an accurate figure-you'd simply be averaging two incorrect numbers to create a third incorrect number. Even a direct crosswind is a handicap, since airspeed over the car ends up being greater than the car's speed over the road-and that can only mean more drag. Rolling friction increases due to the slight steering correction required to hold the car on line against the wind. A precisely sized quartering tailwind can duplicate the effect of no wind at all, but determining the airspeed at which such a breeze zeros out for a given car could keep a Cray supercomputer up nights.

Throw in the effects of electronic speed limiters (some cut off suddenly-check out the Supra's wavy top-speed curve), ladle on gearing and power-curve interactions, and it's obvious that there's no viable way of applying a correction factor to eliminate all the variables.

In addition to environmental factors, each vehicle has its own set of variables; everything from tire pressure and wheel alignment to engine temperature and break-in miles plays a factor. Add in the familiar "normal production-line variations," and it becomes clear why not all Camaros, SC 400s, or any other car models test out absolutely consistently. For evidence, we submit the Corvette LT1. The unit we ran in Bang for the Buck last year (Aug. '94) repeatedly topped out at 172 mph; this time, a different LT1 on a different piece of pavement consistently went 167 mph. Like we said, not even a world-class sprinter runs at a record pace every time.

167 MPHChevrolet CorvetteThough alone on the closed, dead-end road, out of habit I glanced at the rear-view mirrors. They were filled with a view of a 100-foot-tall dust-and-rock rooster tail reminiscent of the exhaust plumes captured by rear-facing cameras on a X-15 rocket plane. But this time, the contrail was from an earthbound rocket ship. It's hard to imagine 167 mph. It's faster than many small airplanes can fly; it's roughly the speed at which jet airliners leave the ground; it's the top speed of the 300-horsepower LT1 V-8-powered Corvette. With its adjustable suspension on the midlevel Sport setting, the Corvette was rock-solid and confidence-inspiring at 167 mph, its pushrod LT1 screaming just shy of the 5700-mph redline in fifth gear. A dozen years after this current-generation Corvette was introduced, it's easily the fastest car available under $50,000. Not only do seven of the slower cars in this test cost more than the Corvette, many far more expensive cars don't come anywhere near the venerable Vette's flat-out performance.