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The 1990 Corvette ZR-1 / Hellcat Connection Revealed: Calibrating the C4 ZR-1 ECM

Corvette Horsepower Emerges From its Dark Ages as a Radical Renaissance. Lotus LT5 Development Engineer Geoff Jeal Revisits Calibrating the C4 ZR-1 ECM

John Gilbert Jun 10, 2015
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There are words that can strike terror into the blood of any true Corvette performance enthusiast. Scary words clumped together into technical terms like exhaust gas re-circulator, positive crankcase ventilation valves, smog pumps, catalytic converters, carbon dioxide emissions, and so on.

All it took was about one year into the 1970s and it was clear Corvette horsepower was about to enter the Dark Ages, and, as history will attest, it wasn’t until 1990 before true supercar performance returned to Corvette powertrain offerings. Recently, a loyal Vette reader spotted an interesting piece of test equipment at the National Corvette Museum alongside Tyler Townsley’s 1988 “King of the Hill” ZR-1 prototype “Queenie” and queried us to learn more about it. We knew it wasn’t a Heathkit guitar amplifier or a Silvertone Hi-Fi, so it must have something to do with calibrating the ZR-1’s Lotus developed LT5 engine.

Epa Calibration Computer 2/15
1990 Corvette Calibration Sensor Connection 3/15
C4 Zr 1 Engine Calibration Phase 1 Brain P8y044 4/15

It’s amazing how prompt and dedicated Corvette aficionados are. We fired off an email inquiry to the National Corvette Museum and received an immediate reply from Katie Frassinelli (Marketing/Communications Manager) with Tyler Townsley’s email address. No sooner had we forwarded our request to Tyler before we got his reply and learned, “What you have in the picture is the equipment used by Lotus to develop the calibration needed to pass EPA specs. I bought it from Geoff Jeal who was the chief calibration engineer for Lotus at the time. Geoff is now the chief of Chrysler powertrains and one of the engineers behind the new Chrysler Hellcat motor.”

C4 Zr 1 Engine Calibration 1986 Mule P8y044 5/15
C4 Zr 1 Engine Calibration 1986 Mule P8y044 Engine Shot 6/15

To help us dig even deeper, Tyler provided us with Geoff Jeal’s contact info, and that’s where things really got interesting.

VM1: The device in the picture is a GM cal [calibration] console. This type of device was used in the days before commercially available calibration software tools such as ETAS Inca and ATI (now the industry standard). In place of the ECU on the car was an extension harness that went down the side of the car under the rocker panel, entering the car through the side of the ABS compartment behind the seats. The ‘umbilical’ was attached to a prototyping stack, which contained an ECU and a separate chip set. This in turn was connected to the cal console.

On the front of the cal console are rotary switches by which you can select various calibration functions (spark, fuel, idle speed control, etc.). Once you had selected the part of the calibration you were working on you needed to reference your personal paper copy of the calibration guide to find the hexadecimal addresses you needed to change and the calculations you need to use to enter the correct calibration. All changes were saved to the RAM memory in the prototyping stack. From there you needed to burn your cal to an EPROM.

VM2: The cal equipment was designed and built in house by GM/Delco.

VM3: There were a ton of projects for GM that did not make production or were concepts for the GM engineers to bring to production: a new four-cam V-8 for the Cadillac Allante (basis for the Northstar), running V-12 and V-16 engines both for Cadillac, an I-6 twin-turbo that made 377 bhp, the electronic damping on the C5/6, etc. was started at Lotus, plus a bunch of smaller projects: active ride control, active noise cancellation, fluid clutches, it goes on and on. A very exciting place to be in the 1980s.

VM4: Where do I start … ZR-1, the original calibration guide (the working document for the calibrators) was in an A4 binder and ran to around 150-200 pages. The software contained around 1,000-1,500 calibratable parameters. The base engine, emissions, and diagnostics could be calibrated by three engineers. For Hellcat, and pretty much all modern cars you can’t print the document because it is so large, it runs to thousands of pages. There are 133,000 calibratable parameters for torque control, OBD, emissions, base engine, and driveability. For Hellcat alone there are 15 calibration engineers, I am also responsible for Viper and the 6.4-liter Apache applications, so the name of the game these days is large teams!

In retrospect, for the general public, the year 1984 signified George Orwell’s futuristic predictions of draconian oppression becoming reality. For Corvette lovers it was the introduction of the first modern Corvette, and signified more exciting things to come.

C4 Zr 1 Engine Calibration Closeup Phase 1 Motor 7/15
C4 Zr 1 Engine Calibration Interior Car To England Of Two 8/15
C4 Zr 1 Engine Calibration King Of The Hill Prototype 9/15
C4 Zr 1 Engine Calibration Ex5008 Ex5023 Koh 10/15
C4 Zr 1 Engine Calibration 1989 Sn4 Pilot Car 11/15
C4 Zr 1 Engine Calibration Epa Exemption Sticker Gm 12/15
C4 Zr 1 Engine Calibration Dana Koh Tag 13/15
C4 Zr 1 Engine Calibration Ed Simmons Scrap Engines England 14/15
C4 Zr 1 Engine Calibration 1987 1989 Vin Assignments 15/15



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