The Z28 option was discontinued for 1975 despite an increase in sales to over 13,000 units in 1974 and similar popularity of Pontiac's Firebird Trans Am. Chevy dropped the Z28 due to ever-tightening emission standards that spelled the end of the higher-output versions of the 350 cubic-inch V8, rated at 245 horsepower (183 kW) in 1973 and 1974. Engines that were offered in 1975 continued to reflect the impact of these regulations in their declining horsepower ratings. Two 350 cid (5.7 L) V8s produced 145 hp (108 kW) and 155 hp (116 kW) (Horsepower losses can seem a bit exaggerated compared to earlier cars, however, their power ratings were now net as opposed to the prior gross ratings. SAE net power ratings (used since 1972) were taken from the engine crankshaft as before, but now all accessories had to be attached and operating, and all emissions equipment and a full production exhaust system had to be in place. These power-robbing additions — along with stringent new emissions laws and the equipment they required — were instrumental in creating the vastly smaller power figures found in subsequent cars.
The manufacturers themselves also sometimes intentionally underrated engines for a variety of motives, notably avoiding provoking the insurance companies and federal regulators into enacting undesirable policies, but also sometimes to prevent lower priced models from stacking up too well on paper against their own more profitable high-end products.). The year 1975 was also the first for the catalytic converter, which was designed as a much more efficient way of reducing emissions than the previous air pump and other smog gear, allowing for finer tuning of engines to permit improved drivability and fuel economy. However, the converter spelled the end of true dual exhausts and mandated the use of lower octane unleaded gasoline, which was not only inferior in antiknock qualities but also more expensive than leaded regular gas, a great disadvantage at a time of dramatically rising gasoline prices in the aftermath of the 1973-74 Arab Oil Embargo.
The catalytic converter and GM High Energy electronic ignition (previously a Z28 option, now made standard for 1975) were advertised among the components of "Chevrolet's new Efficiency System" which was promoted to offer other benefits to 1975 Camaro owners (in comparison to '74 models) that included extended maintenance intervals from 6,000 to 7,500 miles (12,100 km) for oil/filter changes and spark plugs that lasted up to 22,500 miles (36,200 km) compared to 10,000 miles (16,000 km) on '74 models.
A new wraparound rear window was introduced for 1975 and the Camaro emblem moved from the center of the grille to above the grillework and the "Camaro" nameplate was deleted from the rear decklid. Also new block letter "Camaro" nameplates replaced the previous scripts on the front fenders. Interiors were revised slightly with new seat trim patterns and bird's-eye maple trim replacing the Meridian grained walnut on the instrument panel of LT models. Announced for this year was the availability of a leather interior option in the Camaro LT, but never saw the light of day as no production cars were equipped with real hide seats. Other developments included the availability of air conditioning with six-cylinder engines and standard radial tires on all models.
Power door locks were a new option for 1975. The Rally Sport option returned after a one-year absence, but amounted to little more than an appearance package.
Despite the loss of the Z28, Camaro sales remained steady for 1975 at 145,770 units. With the demise of the other ponycars the previous year, Camaro and Pontiac's Firebird were now the only traditional ponycars left on the market, giving GM 100 percent penetration of this segment for the first time ever. Also, despite General Motors' policy against factory-sponsored racing efforts, Camaro began to make a name for itself on the track on the new International Race of Champions (IROC) series with many top drivers winning trophies from behind the wheel of a Camaro year after year until the late 1980s.
Source: Wikipedia, 2011