By Barry Winfield

As six hot cars career along the Firestone test track at Fort Stockton, Texas, competition and apprehension reign among one group of spectators: the guys who, to the tune of more than a half a million dollars, have tweaked these cars into terrifying shape. Taken together, these six monsters produce 2,400 horsepower – enough to run a fleet of stock Toyotas or Fords. A Corvette modified by drag racer John Lingenfelter scarfs up the long, banked track at 189 mph. Race driver Peter Farrell’s dangerously red Mazda RX-7 has been pumped up from the stock 255 horsepower to a mind-boggling 360. A transmogrified BMW 850 boasts a V-12 engine that now belts out 475 horsepower. A flag-yellow Mercedes-Benz 500SL – upgraded by RENNtech of Delray Beach, Florida – struts its US$200,000 stuff, running out of revs before it runs out of power: It screams off at 182 mph and 6,200 rpm.

The aim here, obviously, is to go as fast as physics will allow. In the not-too-distant past, cars were hot-rodded exclusively by the addition of larger carburetors, free-flowing exhausts, high-compression pistons, wider camshafts, or big bore jobs. Some of these techniques are still in use, but any engine modification these days also requires new engine-computer chip strategies to manage the revised operating parameters. The revolution in automotive electronics has spawned an $80 million industry supporting more than a dozen aftermarket chip companies.

Thus, with the BMW 850, the original engine’s computer chip was ditched. With it went the 155-mph automatic speed limiter that many current German and Japanese manufacturers have adopted. In keeping with the car’s brutal new persona, the replacement chip promises a much less sanctimonious attitude.

The car’s tuners – from a company called AutoThority – have already run the car faster than 155 mph, and they are confident that their various tweaks will see it clocking top speeds in the 190-mph range on the Texas circle track. As the car pulls out, a ripple of interest runs through the assembled participants. But then, to our collective surprise, after streaking eagerly to 170 mph, the car hangs there as if held back by an invisible rein. It turns out that the BMW, which sports an all-electronic fly-by-wire throttle system instead of the mechanical linkage most cars use, has two speed limiters. The first one is in the engine-control module chip, the second – at a slightly higher speed – is in the throttle-control circuitry. The guys from AutoThority are mortified.

Such are the pitfalls facing aftermarket car-computer hackers, those guys in the arcane business of recalibrating the chips in car engines to defy the original intentions of their makers.

Now, car manufacturers are not by nature killjoys, but among the factors they must consider when setting up the many values that control the function and performance of an engine are drivability (the smoothness, response, and predictability of a car), durability (manufacturers have to stand by their products for many years and many thousands of miles), and, of course, exhaust emissions (the car has to meet federal or state tailpipe regulations, for a specified period of time, under warranty).

Some owners are less preoccupied with these considerations than they are with power and speed. These people give performance a higher priority than durability. And, until recently, many of them neglected tailpipe emissions altogether. But that’s not an attitude the aftermarket chip industry can afford these days. Thanks to aggressive policing by the Environmental Protection Agency (EPA) and by the California Air Resources Board (CARB) (much of the car chip aftermarket is, predictably, in California), aftermarket automotive companies have to be sure – dead sure – that they do not degrade the exhaust quality of a car they modify. The penalties are dire, with hefty fines levied for each car modified. A few year’s worth of vehicles on the wrong side of the law, and you’re as good as broke. And manufacturers will void vehicle warranties if aftermarket modifications cause cars to fail legal emissions requirements.

Not to exaggerate the problem. Tailpipe emissions tests run by the EPA and CARB – though differing in some details – are programs run on a dynamometer to simulate a cold start followed by an urban driving cycle with periods of idling, as if the car were caught in traffic. Prolonged wide-open-throttle bursts are not tested. So some makers of aftermarket engine-control chips focus on the top end, leaving the original manufacturers’ calibrations much as they were at start-up, idle, and part-throttle settings.

Full throttle at high engine revolutions often gives the big gains anyway. According to Blake Carpenter, chief engineer at Texas-based Hypertech, many production cars run quite rich (a high fuel-to-air ratio) at full throttle, with less spark advance than is optimal for maximum power. This is typical manufacturer conservatism. With that cautious strategy, the car makers are dealing with possible fuel quality fluctuations. The event they fear most is detonation, produced by too low an octane rating, too lean a mixture, too advanced an ignition spark, or a cozy combination of the lot.

(Detonation is that “pinging” or “run-on” that plagues old cars when the ignition is turned off. It occurs when the compressed fuel-air mixture explodes spontaneously in the combustion chamber instead of burning evenly across a rapidly moving flame front. If the conditions are right, detonation – or pre-ignition as it’s also known – does not even require a spark from the ignition system; red-hot carbon deposits or engine parts will do. However it occurs, it’s bad news, eventually leading to serious engine damage and poor performance.)

From the chip hackers’ standpoint, the manufacturers’ cautious approach to full-throttle calibrations leaves them some leeway. At the right levels, lean mixtures and lots of spark mean better performance. And that’s where Blake Carpenter looks for it. He says many cars per-form better with more spark advance and leaner mixtures. Except, that is, for the serious performance cars. Cars like Corvettes and Camaros, he says, are calibrated close to the edge at full throttle. Their designers control detonation problems with piezoelectric knock sensors, which hear the onset of detonation, then instruct the computer to retard the ignition.

The new Corvette LT1 engine, says Carpenter, proved a real challenge: Only after a year of research could any improvements be found. Nothing in the spark and injector values was worth going after. Lots of work on what’s called reverse engineering (analyzing the original equipment values) and plenty of data from fifth-wheel equipment (precision speed-measurement equipment using either calibrated wheels or an optical device attached to the car) led him to the electronically controlled coolant thermostat. It was opening at fairly high temperatures, to speed warm-up in colder climates for better heater and emissions performance. Carpenter punched in a new, cooler value (160 degrees versus the 175-degree stock setting), and the car responded with more power. The LT1, he says, likes cool cylinder-head temperatures.

This protracted investigation starkly contrasts with the routine for tamer vehicles. A 1989 Chevy Lumina Eurosport with a 3.1-liter V-6 engine had so many spark and mixture settings that the car was easily transformed. In fact, says Carpenter, the new calibrations not only boosted acceleration – shaving off about 1.2 seconds from standstill to 60 mph – but also took a surprise toll on Hypertech owner Mark Heffington: During an in-car demonstration, the fifth-wheel display unit leapt off the dashboard and smacked him in the face, chipping a tooth.

After all that, adds a rueful Carpenter, only about two chips sold for that car all year. Clearly, the Lumina is not the car performance-oriented customers snap up. Carpenter says manufacturers seldom tune for optimum power, preferring to tune for 87 octane fuel and emissions performance. By changing only the wide-open-throttle strategies, it’s relatively easy for Hypertech to meet EPA and CARB certification requirements. They submit chip files to show what they’re doing to the chip and usually get an immediate exemption order that allows them to sell the product. Occasionally, however, they are asked to run tests with the new chip.

Ignition and fuel strategies are only two ways to heighten performance. Modern engine control units also guide transmission function, setting shift points and locking or unlocking torque converters at predetermined points. Veteran engine computer hacker John Adrain, of Adaptive Technologies, says he remembers an Infiniti Q45 with a chip from Jim Wolf Racing that picked up 1 1/2 seconds between 60 and 80 mph by simply moving the transmission shift points 400 rpm up the dial.

Adrain would know about engine control: He invented and markets the Prompaq, a device that mounts four separate engine control PROM chips and patches into the car’s computer. Any one of the chips can be engaged by a simple key switch; it loosely resembles the task-switching software on the computer this is being written on. The Prompaq is the ultimate car-tuner’s toy, enabling a driver to select from various performance programs, depending on the application. Say you want a towing strategy that pushes gearshift points up, even on a light throttle, and stays rich and retarded for good cooling: Switch to Position One. Want total acceleration to dust off that pesky Camaro driver? Select Two. Handing over the car to a hyperactive valet? Switch to the chip with the 3,000-rpm cutoff point and pocket the key. Or, after parking, switch to the security chip that disables the engine. Then walk away.

Of course, Prompaq is great for aftermarket chip developers. It’s an easy way to compare various configurations in back-to-back tests without carting around a laptop loaded with engine settings. But Adrain is already moving on. He has filed a patent application for a novel computer piggyback system that lends much greater flexibility to an original equipment engine-control computer. He believes that there’s a real need for continual recalibration of car computers. “For one thing,” he says, “the fuel formulas keep changing.”