J-Body FAQ wrote:
What are the differences between a Cavalier and a Sunfire?
The main differences are the exterior and interior styling. The main body of the two cars is virtually identical, right down to the frame. There is a distinct difference in the rear quarter panel and tail end sheet metal between the Cavalier and Sunfire coupes, but the sedans are identical. The mechanical equipment remains the same for both cars, and both cars have essentially the same equipment available.
To GM, the Cavalier is positioned as the more "value-based" car, while the Sunfire is seen as the more "performance-based" car. It is because of this that the Sunfire receives things such as more sound-deadening material and thicker padding in the dash and seats. Some minor options, such as courtesy lights and assist straps are only found on the Sunfire. Also, the Sunfire GT receives a dual-muffler exhaust system, while the Z24 does not.
According to a phobia list member who works at the Lordstown plant, the Sunfire also receives slightly higher-quality materials than the Cavalier does. For example, bumpers on the Cavalier are made from cheaper thermoplastic olefin (TPO) while the Sunfire receives reinforced injected molded plastic (RIM) bumpers.