When it comes to DIY upgrades for modern performance cars, few products offer a more compelling cost/benefit equation than aftermarket computer-tuning devices. We experienced some of these benefits firsthand a few years ago, when we used one of Hypertech's (since discontinued) Power Programmers to lop more than a tenth of a second off of our Polo Green '96 coupe's quarter-mile times. In addition to the extra urgency at WOT, the Hypertech unit allowed us to activate the engine-cooling fans at lower temperatures, put some extra starch in the upshifts, and even adjust the speedometer calibration to match the car's shorter-than-stock 3.54 rear gears. In a marketplace awash with inflated price tags and dubious performance claims, the affordable, easy-to-use Power Programmer distinguished itself as a true overachiever.
Time and technology march on, however, and when we recently installed one of Trick Flow Specialties' "Fast as Cast" GenX top-end packages on the car, it quickly became apparent that the handheld Hypertech's "one size fits all" programming lacked the power and flexibility we'd need to get the most out of our revitalized engine combo. When an initial attempt at having the ECM reprogrammed on a mail-order basis proved only partly successful (the car ran fine-after a 10-minute warm-up period), it was clear that what our C4 really needed was a fully customized, combination-specific computer tune developed on a chassis dynamometer.
We used the SIM Tampa office's in-house Dynojet chassis dynamometer for our test-and-tune
Dyno-Based Tuning: The Ultimate ECM-Tuning Tool
For all their impressive computing power, most handheld ECM-tuning devices lack one key feature: the ability to "read" powertrain measurements such as spark and air/fuel ratio in real time and make changes accordingly. (While some of these tools do offer the ability to read and modify certain parameters, the range of adjustability offered is typically limited, the idea being to prevent an untrained or injudicious operator from damaging his or her engine.)
By contrast, a dyno-based tune is performed using ultra-powerful software capable of monitoring and controlling virtually every aspect of engine (and, in most cases, transmission) operation. For this reason, it's critically important that you locate a properly trained tuner who has experience with your car's specific type of powertrain-control computer.
Fortunately for us, one of the nation's top tuning specialists, Tony Gonyon, is located just a few hours from our office. Through his Orange Park, Florida-based tuning firm, TunersInc., Gonyon has worked his special brand of binary magic on everything from lightly modified everyday cruisers to turbocharged, 1,500hp Ford GT supercars. A munificent sort by nature, he agreed to drive down and tune our C4 on our office tech center's recently installed Dynojet chassis dyno.
Finding the Power: An Exercise in Incrementalism
Once the car was thoroughly warmed up and strapped to the dyno, Gonyon began the session by plugging his laptop into the car's diagnostic port and taking a baseline read of the engine data. It was at this point that he discovered the source of the idle problem: A false knock reading-most likely prompted by the noisier aftermarket valvetrain components-was causing the computer to retard spark timing by up to 10 degrees. Gonyon used his programming software to direct the ECM to account for the clatter, and the problem instantly disappeared. With the car idling almost as smoothly as a stocker, it was time to start tuning for maximum horsepower.