CHICAGO (Tribune Media) - When electronic controls replaced mechanical devices such as carburetors and distributors, do-it-yourselfers and performance tuners complained, "You can't work on these new cars because computers control everything."

Turns out that you can, especially if you're computer savvy.

Instead of going under the hood to install new parts that generate more power, car owners who may not know a camshaft from a crankshaft can go under the dashboard to install new engine computer software that promises the same results.

Companies that make high-performance computer programs say it takes only minutes to obtain 10 to 20 more horsepower and stronger acceleration without installing new parts, damaging the engine or voiding the vehicle's warranty.

If that sounds too good to be true, auto manufacturers say it is. They warn that the gains are likely to be smaller than the claims and that tampering with factory computer settings can cause damage and void new-vehicle warrantees.

That isn't stopping enthusiasts from souping up their cars with supercharged software that alters the electronic control module (ECM), which controls the air-fuel mixture, ignition timing (when the spark plugs fire), how fast the engine runs, the top speed of the vehicle and other functions.

"We get people calling us on their way home from the dealership, asking if we have an application for their new vehicle," said Rick Rollins, sales and marketing manager for Superchips Inc., a Sanford, Fla., company that sells plug-in chips and modules and "tuned" programs for domestic and foreign vehicles.

Superchips' software runs from about $250 to $650, depending on vehicle, and Rollins said on average it boosts horsepower by 10 percent and torque 13 percent.

Rollins estimates his company's business has increased tenfold the last four years and is up 70 percent this year, though he declines to give sales figures for the privately held firm.

The bulk of Superchips' sales is not to drag racers and hot-rodders but to pickup truck owners who want more muscle for towing. The most popular application is on Ford's Power Stroke diesel, a 7.3-liter engine used in heavy-duty pickups.

"I used to be in the racing business, but now I'm talking to the guy pulling the race car, not driving it," Rollins said.

Hypertech Inc. is another major supplier of performance software, selling equipment such as the Power Programmer III through auto parts stores and speed shops. The handheld device is designed for late-model domestic vehicles with V-8 or V-6 engines and ECMs that have programmable memory instead of removable chips. The suggested retail price is around $400, varying by vehicle and engine.

Hypertech says it increases horsepower by 19, to 264, and torque by 24 foot-pounds, to 327, on a stock 2001 Chevrolet Camaro Z28 with a 5.7-liter V-8. On a 1998 Ford Mustang GT with a 4.6-liter V-8, Hypertech says it increases horsepower by 13, to 202, and torque by 18 foot-pounds, to 243.

Power ratings are measured at the drive wheels on a dynamometer and with premium gas, required to get the maximum benefit.

Here is how the Power Programmer III works:

A connector supplied with the programmer plugs into the vehicle's data collector for the onboard diagnostics system (or OBD II), usually located under the dashboard. The programmer downloads the vehicle manufacturer's computer program and stores it for future use, and then uploads Hypertech's modified program into the computer.

Hypertech's software revises the air-fuel mixture and advances the ignition timing (when the spark plugs fire), which, when combined with higher-octane premium gas, Hypertech says produces more power and quicker acceleration.

The user also can program different shift points for an electronically managed automatic transmission and increase the engine's rev limit and top speed, both of which are governed by the ECM.

Hypertech creates its own engine programs by "reverse engineering" the original programs and "making it perform better than it did from the factory," said Amy Faulk, chief administrative officer of the company, based in Bartlett, Tenn., a Memphis suburb.

"The factories have their hands tied with fuel-economy rules and emissions rules. Their cars may have good performance but not the very best they could. There's room left on the table for us to make some improvements.

"Our customer wants his car to be a little faster than the guy's next door. He's the kind who's just not going to leave his car alone," she said.

At the same time, Faulk says, drivers usually get higher mileage.

"We don't advertise this, but most of the time it improves fuel economy. The vehicle operates more efficiently, and because there is more horsepower and torque, they don't have to use the accelerator as much."

Some customers report lower mileage, she added, because "when you have better performance, you're kind of racing red light to red light."

The company also offers plug-in chips for older domestic models that don't have programmable memory, and more than half of Hypertech's sales are to truck owners.

Superchips also sells a handheld programmer, the Micro Tuner, and its software requires premium gas for best results.

In addition, Superchips offers high-performance software for imports, most of which don't have programmable memory or removable chips. That requires removing the ECM from the vehicle and shipping it to the company for reprogramming.

Dennis Bogdon, director of powertrain electronic controls for General Motors, concedes that using premium gas and advancing the ignition timing can produce a small performance gain and higher fuel economy, though he says, "most customers don't want to pay for premium fuel."

If they go back to regular gas, he warns, the engine could experience knock because the ignition timing no longer matches the octane rating of the gas.

For true tire-smoking acceleration, Bogdon recommends the old-fashioned approach - installing high-performance engine hardware, such as a racing camshaft or cylinder heads and intake systems that allow freer air flow.

"If you're really a serious motorhead, you'll want to put in a different cam, different heads. Then you can match the ignition curve to the hardware, and that's where you get the most bang for your buck," he said, adding that such changes would void the warranty.

Bogdon says the risk with aftermarket software is that emissions levels can increase if it causes engine knock or misfiring.

"There also is potential under severe conditions to damage the catalytic converter," he said. "In our normal development, we know the ramifications of when things start to fail."

Hypertech's Faulk says: "Our products won't override anything that would void the warranty. If your car will pass the emissions test without our product, it will pass with it. But, if it has a problem, it won't cure it."

Superchip's Rollins goes further, saying: "With every Ford application we have, it ran cleaner than any vehicle that came off the showroom floor."

Honda is the most popular import brand with performance tuners, but spokesman Art Garner says Honda seldom sees damage to cars that are under warranty because most modified cars are more than 3 years old and out of warranty.

Whether aftermarket computer tuning violates Honda's warranty "depends on what chips you are installing and what it does. If it eliminates the rev limiter, that would violate the warranty," Garner said, saying it can be hard to tell whether the software has been altered.

"But if a car comes in and it's been slammed, lowered and has big tires, and it has a burned piston, we would start looking for the reasons why," he said.

With a device like the Power Programmer III, it can be difficult for a dealer to tell whether damage was caused by Hypertech's software. The company advises customers to remove Hypertech's program and reinstall the factory software before taking it to a dealer.

"It's not sneaky," Faulk insists, adding that Hypertech isn't stealing proprietary information from the manufacturers. "We're writing our own software, and you're only changing the software."

Superchips and Hypertech guarantee their software but neither promises to pay for repairs, saying their products will not cause damage.