A 40-year-old banker from Greenwich doesn’t seem the most likely hot-rodder. Sure, he may have a Porsche Turbo as well as a Lexus S.U.V. But he’s hardly likely to swap performance tips and tools with a 19-year-old “tuner” in a slammed Civic with a buzz-box muffler and speakers so loud you can hear his music in the next hamlet.

Yet either of them could easily be part of a new generation of tinkerers, people who boost the performance of their cars with electronics rather than elbow grease. The secret? An arcane art known as chipping, replacing or reprogramming a vehicle’s software to change the way it operates. Throw in a new microprocessor, which can cost anywhere from several hundred to several thousand dollars, and your car can have more power, more torque, and more speed. Of course, doing so may also void the warranty and render the car not in compliance with emissions regulations.

A few decades ago, engine components like the ignition and carburetor were adjusted with hand tools. Today, electronics lie at the heart of every facet of a car’s behavior. Separate microprocessors control the engine, transmission, suspension, and other systems. They are intricately programmed to keep drivers safer by compensating for steering errors or monitoring the distance between you and the car ahead of you, they help maximize fuel economy, and they can even change a car’s personality entirely (see “Multiple-Personality Cars”).

It all started in the 1980s, when car manufacturers began using computers to adjust engine settings so that cars could meet ever-tougher emissions standards. An engine-control unit looks at data from dozens of sensors—measuring the motor’s temperature, r.p.m., throttle position, crankshaft position, and more—and regulates the amount of fuel delivered by the injectors and the timing of spark plugs to minimize emissions and boost fuel economy. The cars were far cleaner than older models, but some of the fun and performance had been digitally drained away.

Two notorious examples are the popular BMW 325e and 528e, which together sold hundreds of thousands during the 1980s. Tuned to be as fuel-efficient as possible, they weren’t exactly punchy to drive. In 1985, Dave Welch, a 22-year-old videogame designer at Atari, tore into the programs in one Beemer’s engine-control unit, making it suck up more fuel and generate more power. Thus was born Veloz Car Computers, one of the earliest companies to sell replacements for so-called PROM (programmable ROM) chips.

Chipping exploded in popularity, then fell somewhat out of favor in the 1990s as hundreds of chip shops spewed out products, many barely tested or potentially damaging to engines. Tuner culture (think The Fast and the Furious) brought a major resurgence several years ago. More recently, manufacturers have essentially been chipping their own cars. Virtually every sports and luxury automaker offers performance versions: BMW has its M series, Mercedes-Benz the AMG line, Jaguar the R models. That means the people who chip pricier cars like BMWs and Porsches these days may well race them, says Tim Potts, a car mechanic in Ann Arbor, Michigan, who’s chipped German cars for clients for more than 20 years.

More common is for younger people to work on small, cheap, high-volume cars. The chips are easy to come by—just search the Web for a phrase like “Honda Civic performance chips” and the links spill off the page—and for lower-priced cars can cost just a few hundred dollars. The Honda Civic and closely related Acura Integra are popular transplant recipients, as are various models from Volkswagen, Scion, Mini, Subaru, and Mitsubishi. You can get chips for most high-volume American engines too.

But this doesn’t mean you can’t do a Porsche, if you’re willing to drop a few thousand dollars. For example, new code for a 1997 Porsche Turbo costs roughly $3,500 from G.I.A.C. in Irvine, California, which offers kits for Audis, Bentleys, BMWs, Minis, Porsches, and Volkswagens.

You may be able to chip your car just by buying the chip and wielding simple tools. But as manufacturers seal their systems to prevent just that, it’s increasingly necessary to hook the car to a PC that updates the software in the chip. Also, you get the most bang for your byte when updated control programs are paired with suspension modifications, different wheels and tires, even an added turbocharger—in other words, old-school modifications.

There are downsides to chipping. With very few exceptions—some work performed at Dinan Engineering, based in Morgan Hill, California, is one—changing the control software will invalidate your car’s warranty. Not so bad on a five-year-old Honda, not so good on a new Porsche Turbo. And there are chips that will make your car flunk the emissions tests required in some states. Then again, you can also find makers who’ll claim that they can make your Porsche guzzle less gas and still be as fun to drive.

So what’s it like, driving a tweaked car? Two decades ago, I took one of the more memorable rides of my life in a BMW 533i with Steve Dinan at the wheel. With a new chip, an added turbocharger, and a heavily modified suspension, the car reached 130 m.p.h. in fifth gear in seconds. Luckily, the brakes were modified too.

Back then, chipping was a smart and forward-thinking way to solve a problem: Cautious manufacturers were playing it safe, and were compromising performance as a result. These days, the BMW M5—the factory version of Dinan’s car, with a 5-liter, V-10 engine pumping out 500 horsepower at more than 8,000 r.p.m.—is probably all the car I need. But no doubt someone, somewhere, is planning more.