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.
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.
While the subjects of spark timing and air/fuel ratio (AFR) are sufficiently complex to fill an entire article, the bottom line is that finding the right combination of these two parameters is critical to the task of extracting maximum safe output from any engine combination. Tuning on a chassis dyno is the ideal way to achieve this balance, since it allows the tuner to make minute changes to spark advance and fuel-injector timing over the engine's entire rpm range.
The terms rich and lean are central to any discussion of AFR. A rich combustion mixture-that is, one with an overabundance of fuel-is typically safe under a wide range of operating conditions but less than optimal for generating optimum horsepower. A lean mixture-one with an overabundance of air-makes more power but can become dangerous beyond a certain point. Again, balance is key.
Our C4 started out with an overly rich AFR, which Gonyon tweaked via laptop over the course of several dyno runs until he reached near-ideal readings on the final pull. After settling on a complementary spark curve, he fine-tuned the car's shift points and firmness, rev-limiter settings, cooling-fan operation thresholds, and various other parameters to better suit the new cylinder heads and camshaft. The entire process took a little more than two hours, mostly due to the protracted upload times of the LT1's outdated ECM. (Indeed, we've seen similar tuning sessions take half as long on C5s and C6s.)
The final dyno run of the evening brought readings of 323.39 hp and 302.89 lb-ft of torque at the rear wheels, representing improvements of nearly 52 horses and 7 lb-ft over the session's first pull. While it's perhaps unreasonable to expect similar results from a stock or lightly upgraded car, our test provides ample demonstration of the value of dyno-based tuning on a heavily modified engine combo. Even better, our C4 now operates with a stocker's civility in everyday driving, a faint syncopated patter from the exhaust serving as a subtle reminder of the 400 (crank)-horse performer under the hood. Roll into the throttle, though, and the big rear Nittos claw for purchase, the trans snaps off perfectly timed redline shifts, and the C4's Cyrano schnoz takes on a distinctly skyward cant.
Will these most recent tweaks enable us to hit our previously outlined bogey of mid-12-second e.t.'s in the quarter-mile? We'll know soon enough, when we take the car to nearby Gainesville Raceway for a full dragstrip test session. In the meantime, it's nice to know that the car is performing at the full limit of its capabilities-thanks to the magic of dyno-based ECM tuning.
To see a video of our final dyno pull, click here.