C4 Chevrolet Corvettes - Generation-Four Spotter's Guide

Things You Can And Can't See In '84-'96 Corvettes

Andy Bolig Jan 5, 2010 0 Comment(s)
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Photo by Harry Toche

Change has always been a factor for Corvettes. Being Chevrolet's showcase vehicle, some of the newest and most technologically advanced additions are often bolted to a Corvette first. The changes to the C4, when introduced in 1984, were distinct technological improvements in the structure and design of the vehicle. Throughout the car's production life, the General made changes, constantly improving upon a platform that launched with rave reviews. Today, this gives the prospective '84-'96 Corvette owner a bevy of options to suit their needs, wants, and financial availabilities.

Besides the obvious changes made when Chevrolet introduced the C4 to the public, there was also a change in the mindset of those responsible for making the C4 a reality. Chief Engineer Dave McLellan and a handful of fellow decision-makers determined that a change was necessary, if not mandatory. Like the '53 Corvettes, criticism was forming that Corvette needed performance to match its performance image. Due to the growing concern for clean air and fuel mileage, performance was placed on the back shelf while all of the auto manufacturers were scrambling to meet ever-increasing government standards. Performance paid the price from the squeaky-clean wheel of emissions, limiting the '81 Corvette to only 195 net horsepower from its 350ci V-8, the same horsepower rating as the first 265ci V-8's gross rating in 1955!

Despite these winds of change at Chevrolet, tests were still proceeding on how to satisfy the greens keepers while bringing back the very thing that made Corvette an American icon: performance. While horsepower figures are a major portion of performance, horsepower is not the only element in the equation, especially if you are limited by fuel-mileage requirements. The engineers and designers knew this and began with a completely new mindset toward technology, utilizing new materials not available in prior generations of Corvettes. Before the C4, no new Corvette program had been approved by GM in over 20 years. The time had come.

Dave McLellan reports in his book, Corvette From The Inside, that the benchmark year for horsepower was 1970 with Corvette enjoying LT-1 small-blocks and LS5 big-blocks. While 370 and 390 hp levels were not going to happen overnight, it set a standard to target.

On the other side of the performance coin, the new car had to handle. The goal was 1 g of lateral acceleration, a lofty number usually achieved by only the most serious racing engineers. This necessitated a much wider, high-cornering-stiffness tire. Dave explains that steering changes of just one degree produce over 350 pounds of cornering force per tire, half again the cornering stiffness of a normal passenger-car tire. Therefore, keeping the tire squarely planted to the road was important, and the C4 was designed to be stiff by using stiff springs and heavy rollbars fore and aft. While the early C4s have been criticized for having a harsh ride, most enthusiast drivers know why. Dave and his crew were to meet their intended goal of 1 g, and, most of all, they did it in a production car.

Due to the extensive design and performance targets, the introduction of the C4, which was intended as an '83 model, was delayed a year, with no official Corvettes produced that year. All the Corvettes produced in 1983 were certified as '84s regardless of the actual delivery date. From there, it was a 12-year parade that was to become the fourth-generation "C4" Corvette.

Let's take a look at some contributions and significant changes that happened to Corvette through the C4 years, and the effect they had on Corvettes to follow.

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1983
This is where it all started. While you can forget about ever owning one, you can see a real '83 Corvette at the National Corvette Museum (www.corvettemuseum.com). This is the only '83 known to exist today. It is the foundation that all other C4s were built upon.

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1984
What You See: The first obvious item is the carryover of the Cross-Fire engine. GM realized that performance and fuel economy meant having fuel control. Cross-Fire was an early attempt at controlling the V-8's fuel diet and, while it helped, it still didn't give enough control since there were two injectors for eight cylinders.

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What You Don't See: In an attempt to provide fuel mileage that met government standards and performance that met buyers' standards, GM also carried over the 700-R4 automatic from the '82 Corvette. New was the 4+3 manual transmission. Calling it a manual transmission is a bit of a misnomer because the front portion is basically a four-speed transmission with an overdrive unit mounted behind it that operated on the top three gears. GM was on the verge of losing its production source for transmissions, so joining with Doug Nash on these overdriven standard transmissions bridged the gap until something better was designed. These transmissions can be found in any standard-equipped Corvette from '84-'88.

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1985
What You See: The big news of 1985 was the switch to Tuned Port Injection for the engine. Having individual injectors for each cylinder gave much more control over the fuel trim of the engine; the tuned-length runners helped boost torque to 40 lb-ft, and horsepower increased from 205 to 230. This shaved almost a second off the previous year's quarter-mile times at the track. Also, the air was regulated by a single throttle body (no more equalizing throttle bodies) and the amount of air fed into the engine was measured by a Mass Air Flow meter (MAF). This helped increase fuel mileage because a 14.7:1 air-fuel mixture was easier to maintain.

What You Don't See: Along with added control of the fuel, the '85 Corvette's computer was upgraded to better control engine performance. The suspension harshness issue was addressed, netting a better ride.

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1986
What You See: Convertibles were back! Corvette was pacing the Indy 500, so what kind of pace car would it be if it weren't a convertible? Also, with the introduction of the convertible came aluminum heads for Corvette. Originally, only the convertibles had them but it wouldn't be long before all Corvettes became light-headed.

What You Don't See: Another advancement for the C4 was the introduction of ABS (antilock braking system), making the car significantly safer. This was also the first year for VATS (vehicle anti-theft system). Note the little pellet on the stem of your ignition key. It's actually a resistor that makes contact inside the ignition to let the computer know it's OK to start the car. Also, the caster was changed in the front-end alignment from 3.8 to 6 degrees. This helps keep the car more stable straight-line and prevents wander while driving.

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1987
What You See: This was the first year for the B2K option, also known as the Callaway Corvette engine, shown in photo.

What You Don't See: This was the first year for a roller camshaft and lifters inside the engine.

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1988
What You See: Since there were no Corvettes produced on the 30th anniversary, GM decided to celebrate the 35th Anniversary Edition. "White" is the best way to describe one of these special edition coupes-white on the wheels, exterior, interior, steering wheel, beltline molding, and seats. Picture a white sheet of paper in an Alaskan snowstorm. Also, Chevrolet produced 56 street-legal Corvettes for the SCCA Corvette Challenge Series.

What You Don't See: There were several changes to the chassis of the '88 Corvette. Larger brakes were added to the Z51 suspension-optioned cars, and all '88 Corvettes got new dual-piston calipers up front and upgraded rear calipers that used the brake pads for the emergency brake rather than an internal brake-shoe assembly.

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1989
What You See: The new ZF six-speed manual transmission was first installed in '89 Corvettes in preparation for the upcoming ZR-1.

What You Don't See: You could call the '89 production year a year of "lasts" rather than "firsts." This was the last year for the Corvette Challenge Series, and Bowling Green built 60 cars for competition. Also, the digital dash was phased out as was the MAF sensor, replaced with a MAP sensor that sensed manifold pressure instead of airflow.

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1990
What You See: This was the first year for the ZR-1. The special ZR-1 LT5 engine was designed by Lotus and built by Mercury Marine. The exotic four overhead cam engine burst on the Corvette scene, producing 385 hp. A hybrid digital/analog dash was installed in the '90 Corvettes, featuring a digital speedometer with an analog tach and secondary gauges.

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What You Don't See: The '90 Corvettes had improved ABS and yaw control within their electronics system; and the heart of that system, the computer, was moved from under the dash to a more accessible position on the driver side, under the hood.

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1991
What You See: The big news for '91 was the updating of the front and rear (non-ZR-1) fascias. The more rounded front featured wrap-around lights, and the body side molding was painted the body color.

What You Don't See: FX3 and Z51 were combined to make a new RPO Z07 featuring selective ride control with the performance-handling package. RPO Z07 was designed for aggressive driving or competition, and adjusted the ride from firm to very firm. Also, an oil-pan float was installed to alert the driver of a low oil condition. This was also the first time that delayed power was installed in a Corvette, allowing the occupants to listen to the radio or operate windows after the key was turned off. This was also the last year that Callaway B2K Corvettes were available.

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1992
What You See: The big news for Corvette in 1992 was the introduction of the second-generation small-block, dubbed the LT1. This new offering was under the direction of Anil Kulkarni and focused on cooling issues as well as improved fuel/air control.

What You Don't See: The LT1 produced 20 percent more power, had better fuel mileage, and met emissions standards better than the L98 (Tuned Port engines). Along with the new engine, synthetic oils were introduced which eliminated a need for any oil coolers. Automatic Slip Regulation made its way into Corvette in '92 as a standard feature. The one-millionth Corvette was built as a '92 model.

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1993
What You See: Corvette was back celebrating anniversaries on even numbers again, and this year was its 40th. A special Ruby Red Anniversary Edition was available in all models, and all leather seats installed in Corvettes for '93 had "40th Anniversary" embroidered into the headrests. The '93 Corvette was the first auto sold by GM to utilize a passive keyless entry (PKE) system.

What You Don't See: The LT1's engine noise was made quieter by changing to a composite valve cover instead of the earlier metal covers and insulating it better from the rest of the engine. Also, the exhaust-valve closing velocity was reduced through camshaft lobe modification. Horsepower remained at 300, but torque increased another 10 lb-ft as a result of cam reconfiguration.

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1994
What You See: The National Corvette Museum opened in 1994. Two new colors were added-Admiral Blue and Copper Metallic-with only 116 Copper Metallic Corvettes produced before the color was discontinued. ZR-1s went to a non-directional wheel unique to ZR-1 Corvettes.

What You Don't See: A new sequential fuel-injection system was introduced that injected fuel to only the cylinder that needed it instead of firing an entire bank of cylinders in a batch. The transmission also received electronic upgrades. Instead of relying on a throttle-valve cable to regulate fluid pressures inside the transmission, electronic solenoids were used which gave more control to the operation of the shifting characteristics of the trans. Corvette owners would be required to step on the brake before shifting out of Park.

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1995
What You See: Corvette was pacing the Indy 500 again and GM offered a dark purple and white Pace Car to commemorate the occasion.

What You Don't See: This would be the last year for the ZR-1. The dash in '95 Corvettes was improved by providing better mounting of the CD player to prevent skipping. Several Velcro(r) strips were included under the dash assembly to eliminate squeaks and rattles. All '95 Corvettes received the upgraded antilock/traction-control system as well as the larger brakes previously installed only on ZR-1s.

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1996
What You See: GM wanted to protect the last year of C4 production numbers so it offered several different editions to help grab customers who might wait until the next year's C5 was offered. Grand Sports and Collector Editions, as well as the other models, were available with the updated LT engine: the LT4. With redesigned heads, camshaft, intake, and roller rockers, this engine was capable of cranking out 330 hp instead of the LT1's 300. The LT4 was only available with a standard transmission, and all Grand Sports came equipped with the LT4.

What You Don't See: Electronic control took on a larger role for the '96 production year. The suspension RPO FX3 was dropped and replaced with F45. The difference between the two suspensions was that FX3 adjusted all four shocks simultaneously, whereas F45 adjusted each shock individually every 10-15 milliseconds, which equates to approximately every foot of road surface at 60 mph. Also, due to the computer's increased role in engine/transmission/suspension management, the number of identification codes to identify a problem increased from 60 to 140. Once again, Corvette regained the top spot in AutoWeek's annual subscriber survey of American cars (July 1, '96) in which readers had the most pride. It pushed Viper into second place.

In a short 12 years, Corvette has progressed from a great-performing sports car, reeling in accolades using only the most basic of electronic computer technology, to a refined canyon carver, producing historic amounts of horsepower and performance using technology that dwarfs its predecessor by light-years. Horsepower was back and it was clear that GM wasn't going to be deterred from installing as much as possible in every Corvette. Of course, it had to be emissions-friendly as well a great performer, which it grew into. The forward thinking that went into the C4 improved the current Corvette, but also laid a foundation, the benefits of which would be reaped well into the next generation.

So the next time a C5 owner tells you how great their car is, just say "You're welcome."

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Mandatory Reading For C4s
The C4 Corvette Sourcebook, by John Loughmiller
The Heart Of The Beast, by Anthony Young
How To Understand, Service and Modify Corvette Fuel Injection & Electric Engine Management, by Charles O. Probst
Corvette From The Inside, by Dave McLellan

The Ins And Outs Of C4 Ownership
In: ZR-1's specially coated windshield with opening for "Electronic Devices" such as a radar detector

Out: This "special film" delaminated badly, hindering the driver's vision.

In: The desire to put performance back into Corvette returns with the C4.

Out: Until '92, Corvette still had to breathe through a single exhaust.

In: Return to convertibles in '86.

Out: Needing braces to eliminate shake once the top was removed.

In: Corvette came into the computer age with faster processors and more capability during the fourth generation.

Out: Hiding that computer under the dash on '89 and earlier cars.

In: LT5s, LT1s, and LT4s.

Out: The exotic nature (cost to repair) of LT5s and hiding the Opti-spark distributors under the water pumps in LT1s and LT4s.

In: ABS and ASR

Out: People who feel they are "good enough drivers" to never need ABS or ASR.

In: Removable Tops

Out: Needing to carry a ratchet and Torx bit to remove the roof.

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