The first IROC (International Race of Champions) season (1974), started on October 27, 1974 and used the Porsche Carrera RSR. Presented as a sort of auto-racing all-star game, the International Race of Champions utilized identically-prepared, evenly matched stock cars of the same make and model, set up by a single team of technicians (historically, NASCAR veterans Dick Trickle, Dave Marcis and Jim Sauter) in an all-out effort to derive a world champion based solely on driver ability. The very next year, Chevrolet came on board and the IROC series began using the Camaro as the official vehicle. The series ran continuously from 1974 to 1980, then, when the economy took a nosedive, it was suspended for three years and then resumed in 1984. Once reborn, one noticeable change was the introduction of the third-generation Camaro into the series.
As a hat-tip to the race that spawned it, Chevrolet introduced the IROC-Z model of the Camaro in 1985. Offered as an option package on the Z28, the Camaro IROC-Z featured an upgraded suspension, lowered ride height, specially valved Delco-Bilstein shocks, larger diameter sway bars, a steering/frame brace known as the "wonder bar", a special decal package, and an optional Tuned Port Injection system taken from the Chevrolet Corvette. It also shared the Corvette's Goodyear "Gatorback" unidirectional tires in a 245/50/VR16 size vs. the Corvette's 255/50/VR16 size, and received unique new aluminum 5-spoke 16-by-8-inch wheels. The new wheels were designed with different offsets front and rear, resulting in the words "Front" or "Rear" cast into the wheels to distinguish which wheel went where.
The Camaro IROC-Z was on Car and Driver magazine's Ten Best list for 1985. The 305 c.i. 5.0-liter TPI LB9 was rated at 215 hp (160 kW), with the 4-bbl 305 LG4 at 155 hp, and the 4-bbl High Output 305 L69 at 190 hp (142 kW). A total of 2,497 L69 IROC-Z models were made for 1985. The LB9 was available only on the Z28 and the IROC-Z model with the TH700-R4 automatic transmission. A total of 205 IROC-Zs equipped with the LB9 305 with the G92 (Performance Axle Ratio) option were made in 1985. The G92 option upgraded the rear axle gear ratio from 3.23 to 3.42.
Also new for 1985, all Camaros featured refreshed noses, and new deeper valances and front spoiler for the Z28 and the newly introduced IROC-Z. The speedometers no longer had the unique double-pointed needle that simultaneously read mph and km/h: they were replaced by conventional single-pointer 85 mph (137 km/h) units.
For 1985 a (1C5) RPO California IROC-Z was also made, Chevrolet's California Marketing Group came up with the idea and it was for sale in California only. A total of 250 black and 250 red examples were produced. They were all equipped with the 5.0 TPI LB9 engine and TH700-R4 automatic transmission. All came equipped with the IROC-Z fog lights, wheels and ground effects, but with the base Camaro's hood (no louvers), rear deck lid (no spoiler), and no exterior decals.
A newly required Center High Mounted Stop Lamp (CHMSL) was installed on the Camaro. 1986 was the only year to see this attached to the outside hatchback glass on base model Sport Coupes, Z28s, and IROC-Zs except for 1987 base models that did not have a spoiler. This was the final year for the L69 5.0 305 HO 4-bbl option, of which 63 were built for racing in Canada's Player's series and 11 for public sale, making a total of 74. The 2.8 L V6 was now the standard engine in the base model, replacing the 2.5 L I-4 model. The 305 TPI LB9 horsepower rating dropped from 215 hp (160 kW) to 190 hp (142 kW) in the IROC-Z models. All V8 engines received a new one-piece rear main seal. Braking performance was 139 feet from 60mph.
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The 350 TPI engine with automatic and 305 TPI with 5-speed manual transmission were available for the first time in the IROC-Z. The new 350 (RPO code L98) was available only in the IROC-Z with an automatic transmission. The TPI 350 motor was visually distinguishable from the TPI 305 as the bumper cover decal had "5.7L" added to the "Tuned Port Injection" decal. It can also be determined by checking the VIN (8th character, F=305, 8=350). The 305 TPI equipped with automatic transmission came with 190 hp, while the Manual 305 TPI got a 215 hp (160 kW) rating. The 350 L98 gave a boost to 225 hp at 4,400 and 330ftlb at 2,800. All V8 engines received hydraulic roller lifters and a new valve cover/head design. Valve covers featured new sealing and center bolts in the valve covers. Heads featured a new raised lip for improved valve cover sealing and the two center intake bolts were changed from 90-degree orientation to 72 degrees. G92 and L98 cars got the Borg-Warner HD 7.75-inch (197 mm) four pinion rear end, produced for GM's Holden of Australia (Firebird WS6 cars went to this unit in 1986). These units can be identified by their 9 bolt (rather than 10) differential cover that has a rubber drain plug. The Borg-Warner logo is also cast into the bottom of the differential case. This rear axle came with tapered rather than straight roller bearings and a cone-clutch rather than disc-clutch limited-slip unit. These units came painted black from the factory while most others were bare metal. All 1987 350 TPI L98 IROC-Zs required 3.27 gears, J65 rear disc brakes, G80 limited-slip differential, and a KC4 engine oil cooler.
The largest visual change this year was the CHMSL (third brake light) was now mounted inside the rear spoiler instead of on top of the rear hatch (except the base coupe without the spoiler option - on those cars it remained on top of the hatch like the previous year). The Berlinetta was no longer available this year, replaced with a new LT model, while the base Camaro and Z28 continued as before. 145 mph (233 km/h) speedometers became standard in the IROC-Zs and Z28s with tuned port injected engines while the carbureted Camaro models and 2.8 liter V6 retained the 85 m.p.h.speedometer.
Other changes included a Camaro convertible that was introduced for the first time since 1969 as a regular production option. Available on the Sport Coupe, LT and IROC-Z, the conversion was performed on t-top equipped Camaros by American Sunroof Company (ASC). A total of 1,007 were produced in the first year of production. The 1987 model year marked the 20th anniversary of the Camaro and the convertibles were considered the anniversary editions and included a dash badge that read "20th Anniversary Commemorative Edition". Some 1987 T-Top models were made into convertibles by ASC after the customer took delivery. This is why there are some convertibles with the body VIN code of 2, meaning they were coupes, not convertibles (which have a body VIN code of 3). This was also the last year of production at GM's Norwood, Ohio, facility as sales continued to decline consolidating Camaro assembly to the Van Nuys factory located in Southern California.
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The Camaro line was greatly simplified this year, starting with discontinuing the slow-selling LT model, and dropping the base Z28. The IROC-Z package proved popular and the package became standard on Z28s. This resulted in two models remaining, the base coupe and the IROC-Z. Without the Z28 to bridge the gap between the base Camaro and the flagship IROC-Z, the previously standard aluminum 16-inch 5-spoke wheels were now an option - "base" IROCs now got the previous year Z28's aluminum 15" 5-spoke wheels (which also became standard on the base coupes) and P215/65-15 tires. Also, the old Z28's ground effects and spoilers were now standard on the base Camaro coupes. Base models received a new raised spoiler for the first half production year.
All engines were fuel-injected this year; the 2.8 (173) running 135 HP at 4,900 rpm and 160 lb.ft at 3,900 rpm, the 5.0L 305-CID V8 gained throttle-body injection, bringing net horsepower to 170; the 305-CID TPI manual transmission models were rated at 220 HP at 4,400 rpm and 290 lb.ft at 3,200 rpm, Automatic at 195 HP at 4,000 rpm and 290 lb.ft at 2,800 rpm and the 350-CID TPI got a small boost to 230 HP at 4,400 rpm and 330 lb.ft at 3,200 rpm. G92 (performance axle ratio) available only on IROC-Z with 5.0 TPI (LB9). All 1987 350 TPI L98 IROC-Zs came standard with the 3.27 BW rear end and everything that was included with G92 but did not have the G92 RPO code because it was not mandatory; this changed in 1988 however when a 2.77 rear was standard and G92 had to be specified to get the 3.27 differential. The IROC-Z was also treated to some small cosmetic changes. The "Z28" logos on the ground effects below the doors and on the rear bumper changed to read "IROC-Z". The large IROC-Z call-outs on the door moved from the front of the doors to the back, to put some space between the logos. Option code DX3 offered buyers the option of deleting the IROC-Z's door decals and stripes for a $60.00 credit. Optional 16" aluminum wheels were redesigned with two lines instead of one large line in each spoke, and center caps backgrounds changed from black to silver. Dash badges on the IROC still read "Z28" on top and "IROC-Z" below. The VIN code 8 is the engine code for a real TPI 5.7L IROC.
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To take an IROC-Z coupe to the maximum performance extreme in 1989, when the G92 Performance Axle was ordered with no air conditioning (C41), RPO code 1LE was automatically triggered. This included extra equipment intended to make the IROC-Z more competitive in SCCA Showroom Stock road racing events: larger 11.65-inch (296 mm) rotors with 2-piston aluminum calipers from PBR; an aluminum driveshaft; a special baffled fuel tank; specific shock absorbers; and stiffer suspension bushings. The fog lamps were also deleted. The 1LE was simply an option combination, not a separate package or model that dealers were aware of the existence of, resulting in 111 cars built with 1LE equipment in 1989.e with the TH700-R4 automatic. 1989 was also the last year any third-gen with the B2L RPO 350 TPI L98 engine could be ordered in combination with the CC1 RPO removable T-Top roof panels.
Power ratings also varied in the 305 from 170 hp (standard RPO L03) to 230 hp (RPO LB9 with manual transmission and RPO N10 dual catalytic converter exhaust) and a boost to 240 hp for the 350 with RPO N10 respectively.
IROC-Zs with the TPI 350 had the 2.77 rear axle ratio as in the previous year, but the optional RPO G92 Performance Axle package modified the ratio to 3.27 for the TPI 350, and 3.45 for the TPI 305 with manual transmission. RPO G92 also included the aforementioned dual-converter exhaust; 4-wheel disc brakes (RPO J65); engine oil cooler; P245/50ZR16 Goodyear Eagle unidirectional tires; a 145 mph (233 km/h) speedometer; and a tachometer with a 5,500 rpm red line. A total of 1,426 IROC-Z coupes were equipped with the Performance Axle package in 1989.
To take an IROC-Z coupe to the maximum performance extreme in 1989, when the G92 Performance Axle was ordered with no air conditioning (C41), RPO code 1LE was automatically triggered. This included extra equipment intended to make the IROC-Z more competitive in SCCA Showroom Stock road racing events: larger 11.65-inch (296 mm) rotors with 2-piston aluminium calipers from PBR; an aluminum driveshaft; a special baffled fuel tank; specific shock absorbers; and stiffer suspension bushings. The fog lamps were also deleted. The 1LE was simply an option combination, not a separate package or model that dealers were aware of the existence of, resulting in 111 cars built with 1LE equipment in 1989.
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The 1990 model year finished the lowest production to date (35,048), due to a truncated 1990 model run followed by the early introduction of the face lifted 1991 models. 1990 also marked the final year for the IROC-Z; Chevrolet had decided not to renew its contract with the International Race of Champions.
This year was the first year for an airbag to be offered in any F-body. The new airbag came along with a new "half-moon" gauge cluster, that was offered only in 1990–1992 Camaros. The sharp edges on the dash surfaces were rounded and the lettering on gauges switched to yellow from white. 1990 was a distinguishable model year as it was the only third-generation Camaro that did not feature the updated ground effects of the 1991–1992 models but did have the newer interior/dash features. The 2.8 L V6 was upgraded to the 3.1 L V6.
The RPO code 1LE was again available in 1990, triggered as in the previous year by RPO G92 Performance Axle combined with no air conditioning on the IROC-Z coupe. Only 62 Camaros were built with 1LE equipment in 1990.
The Last 1990 Camaro Rolled off the line on December 31, 1989.
Camaros in IROC-Z trim that were equipped with the 5.7 TPI Motor received a slight horsepower increase to 245 at 4,400 rpm and torque numbers also rose to 345 at 3,200 rpm.
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