A Timeline of Corvette Fuel Injection

Fuel Delivery Phases

Andy Bolig Jun 30, 2003 0 Comment(s)

Without carrying over the technology from the ZR-1, GM did the next best thing. It designed an intake with runners that were a compromise from the long Tuned Port and the short LT1 and LT4 engines. The result was the LS1, which was released for '97 Corvette production.

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Like the TPI runners, the LS1 intake runners cross over to the cylinder on the opposing bank of the engine, but they are much closer to the LT1 in length at around 10 inches. Also, the port configurations where the intake meets the head is different from previous designs. It is much taller than the ports on any other small-block. It's designed to have good flow while still retaining sufficient velocity at lower rpm, which helps the engine produce more torque. In '01, GM improved this intake design for the LS6 that was installed in Z06 Corvettes.

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Other improvements to the fuel injection for this new engine were the use of composites and new-style seals for the mating surface. Also, a Throttle Actuator Control system (TAC) was implemented on the '97 and later Corvettes. This new system used motor control of the throttle body to control idle and operation of the engine for a complete drive-by-wire system without any throttle cables. This new engine with its new fuel-injection system put the base Corvette's engine at 345 hp--once again, getting close to that 1hp/ci milestone, only this time with much better driveability and fuel mileage. All because of the inclusion of electronics in fuel injection to help control fuel.

The MAF sensors changed as fuel-injection systems became more intricate. The '85-'89 Corvettes used a Bosch MAF (bottom), while '94 and later Corvette engines use an AC/Delphi MAF (upper left). Both MAF sensors operate on the same theory of a heated wire used to measure the amount of air entering the engine. The Bosch MAF operated on an analog signal of varying voltage, and the AC/Delphi MAF used a digital signal to the PCM. The Bosch unit emits a voltage signal, typically .04-5 volts; while the AC/Delphi unit emits a signal in the 32-150-mHz range which is converted from the voltage variation in the hot-wire circuit. The Bosch MAF also uses a Burn-Off cycle each time the engine is shut off to clean the wires within the MAF. The newer AC/Delphi unit does not use a burn-off cycle, so it's even more imperative to keep a clean air filter in your Corvette.

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In '01, GM increased the size of the MAF from 74mm to 85mm, and included the Air Intake Temperature sensor in the MAF rather than further down the intake ducting. Also, the screen was removed from the '02 Z06 Corvettes (upper right).

GM returned to Bosch injectors for the LS1, although some changes were made over the years. The '97 and '98 Corvettes used 26-pound injectors. GM changed them to 24-pound injectors for the '99 and '00 production run, and bumped up to 28-pound injectors in '01.

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From the very first efforts with fuel injection, the goal has always been the same: better fuel control, economy, and lower emissions. Achieve all three of these, and you will have reached the ultimate goal--higher performance. Where will it stop? Will we ever reach a performance plateau where further improvements will require a dramatic change? Possibly, but not yet. Fuel injection has evolved throughout the generations, sometimes revisiting ideas that had been shelved for a "better way to do it."

Currently, the buzz at GM is the idea of "dropping cylinders" by shutting off fuel to cylinders when the car could actually be powered by a six-, or even a four-cylinder engine. Owners of older Cadillacs may remember the 4100 series of engines that attempted to use this Displacement on Demand theory of 4-6-8 cylinder engines. Not widely received then, it was possibly too far ahead of its time. The processors in today's Corvette are so far advanced from what was available then, and the mechanical technology has advanced so much from those early pioneering days that, if the timing is right and the design is solid and reliable, this advanced technology may one day become just like all the others: a milestone in the ever-advancing evolution of EFI.


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