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C4 Corvette PCM Programmer - Getting with the Program

We Put Hypertech's Power Programmer III To The Test

Jay Heath Sep 12, 2007
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Performance-oriented computer tuning for cars has been around since Michael Jackson had a nose, and devices preloaded with various forms of binary thaumaturgy have figured prominently in enthusiasts' power-improvement regimens for almost as long. The enduring appeal of such items-chiefly plug-in PROM chips and handheld programmers-isn't difficult to understand. They're dead simple to use, relatively affordable, and, with few exceptions, capable of improving performance and driveability by a noticeable (if not always quantifiable) degree.

It was the latter element-effectiveness-that we set out to evaluate, using our '96 automatic coupe as a four-wheeled lab rat. As one of the oldest and most highly regarded firms in the tuning business, Hypertech was a natural choice to supply the hardware. The company sent us an application-specific Power Programmer III unit, versions of which are available for all Corvettes manufactured since the '94 model year. (Got an older model? Hypertech offers chips and other upgrades for Vettes going all the way back to 1981.)

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Hypertech's Power Programmer III comes complete with an ALDL cable and a refreshingly coherent user's manual. Retail price is $399.95.

Fortunately for your tool-averse narrator, "installing" the Hypertech Power Programmer III couldn't have been easier. Unlike many of the aftermarket parts we've sampled in the past, the Hypertech unit came with excellent, step-by-step directions that appeared to have been written by someone with more than a kindergartener's grasp of written English. We accomplished the whole job in just under 15 minutes, most of which were spent sitting idly while the HPPIII uploaded its customized tuning to the Vette's computerized brain.

Features vary slightly by vehicle year and model, but the HPPIII for our '96 included the following:

* Power Tuning
* Shift Points (raise/lower)
* Shift Firmness (enhance)
* Top-speed Limiter (remove)
* Speedometer Correction (for aftermarket gear ratios)
* Cooling-fan Engagement Points (lower)
* Rev Limiter (raise/lower)

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The HPPIII communicates with the car's PCM through the diagnostic port located beneath the dashboard. Just plug in the programmer, turn the key to the "On" position (but don't crank the car), and follow the on-screen instructions.

Given the lightly modded nature of our '96, we decided to keep our tinkering to a minimum. Aside from installing the Power Tuning, we dialed in the shift-improvement function and the lower fan-engagement thresholds. We also deleted the built-in top-speed governor, just in case a blast beyond the car's factory-rated max velocity of 165 mph should become necessary at some point. Everything else was left just as GM intended.

With the programming installed, it was time for a test drive. The first thing we noticed was the enlivened operation of the 4L60E trans. Downshifts were quicker and crisper, and the car would break its 315mm rear Goodyears loose (sometimes very loose) on a full-throttle One-Two upshift.

Also of note was the significantly cooler operation in everyday driving. Previously, coolant temps could climb as high as the mid-220-degree range in stop-and-go Tampa traffic. But thanks to the lower fan-engagement thresholds provided by the HPPIII programming, the big LT1 now rarely topped 195.

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Once the HPPIII has established a connection with the car's powertrain computer, a series of prompts will appear on the LCD screen. Pushbutton controls are so easy, even an editor can use them.

Snappier shifts and lower engine temps are one thing, but for a list price of $399.95, the HPPIII had better be worth something in the horsepower department, right? We're happy to report that our '96 picked up 3 hp and 8 lb-ft of torque at the rear wheels, bringing the tallies to 280 and 301, respectively.

While that might not sound like much of an improvement, we figured the slight extra grunt-coupled with the quicker, crisper shifts-might be worth 0.05 or so in the quarter-mile. As it turned out, our estimate proved conservative. (See the accompanying data for a full rundown of the car's track performance.)

Like any prt a porter performance part, the HPPIII does have its limitations. It does not, for example, allow for full manipulation of the car's computerized spark and fuel values, la LT1 Edit. Accordingly, we would not consider it appropriate for vehicles equipped with forced induction or internal engine upgrades, modifications that require ultra-precise regulation of ignition advance and air/fuel ratios.

For now, however, the Hypertech Power Programmer III's impressive blend of virtues makes it a useful addition to our C4's modification arsenal. If only Jacko had aged as gracefully.

Baseline Average: 13.455 @ 102.02
Hypertech Average: 13.300 @ 103.21
Avg. Improvement: 0.155 seconds, 1.19 mph

*Car was previously modified with Comp 1.6 roller rockers and springs, an SLP cold-air induction package, and Mid America MAF ends.

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Before-and-after dyno testing found the Power Tuning to be good for an extra 3 hp and 8 lb-ft of torque at the rear wheels. Even better, the car dropped more than 0.155 second at the strip. Cooler running and more-vigorous shifts from the 4L60E trans are additional pluses.

From the Logbook
Launch Control: With its fat, GS-spec rear tires and 3.07 gearing, our '96 was a model of consistency at the tree. After experimenting with various launch methods, we settled on simply flat-footing the gas pedal at the last yellow. The payoff? Tidy, spin-free launches and 60-foot times as low as 1.966.

Keep Your Cool: Unlike an all-aluminum LS engine, our Vette's iron-block LT1 preferred to run cool at the strip. In fact, we achieved our best e.t.'s with engine-coolant temps in the 160-175-degree range. Any hotter, and performance suffered noticeably. Note, however, that the one pass we made at an ice-cold 155 degrees ended up being the day's slowest.

Supporting Player: To keep the engine running as cool as possible on the street, Hypertech suggests installing one of the company's Power Stat low-temperature thermostats concomitantly with the HPPIII. This was unnecessary in our case, since we had already swapped out our car's stock thermo for a 160-degree unit (see "What Price Performance?" Nov. '06).

Brain Drain: Because the uploading process places a heavy burden on the electrical system, Hypertech recommends starting the car to recharge the battery between programming sessions. Take our word for it: They're not kidding.

Premium, Please: Much, if not all, of the horsepower improvement available with the HPPIII is attributable to the hotter spark timing built into the Power Tuning feature. More spark demands higher-octane fuel, which is why Hypertech specifies premium-grade gas for any car thus programmed. Of course, you were running premium in your Vette anyway, right?


Bartlett, TN 38133



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