The series was exclusively built in a two-door coupé body style (except for convertibles made by Baur).

In 1978, the 3-series received its first fuel-injected six-cylinder in the 323i as a flagship performance model; and in 1981, a bottom end detuned 1.6 L was offered in the 315.

[8] The frontal view of the new car was dominated by the BMW trademark kidney grille standing out clearly from the radiator cover.

[23] In an effort to further lower the price, the 315 also had bumpers with exposed screws, a vinyl-covered parcel shelf (this was carpeted on all other E21 models), no map pockets on the doors, R2 double filament headlamps (rather than halogen units), and a single external mirror.

The 316 was the base model for years 1975 to 1981, fitted with a 1.6 L (98 cu in) M10 engine producing 90 PS (66 kW; 89 hp).

[14] In 1980 the engine size increased to 1.8 litres (after the 318 carburetor version was discontinued), while the model badge remained "316".

[23] The 318 was a mid-range model that was powered by a carburetted four-cylinder engine, producing 98 PS (72 kW; 97 hp).

[14] The rear suspension design causes camber changes, which can introduce "snap oversteer" at the handling limits.

It has the M10 four-cylinder engine with Bosch K-Jetronic fuel injection, and a limited slip differential was available as an option.

The new range-topping 323i model was introduced, featuring 2.3 L with 105 kW (141 hp), which gave the 323i a top speed of 200 km/h (124 mph).

Options include power steering, a 5-speed close-ratio 'dogleg' sport gearbox, and 25% limited slip differential.

This fuel-injected 1.8 L M10 was also sold in Sweden with 320i badging (with a higher level of standard equipment to distinguish it from the 318i), because the 320/6 was never certified for sale there.

Six-cylinder models were not sold in America, because the E21 versions of the M20 engine did not meet U.S. emissions regulations at the time.

[citation needed] The 320i models sold in the United States have a thermal reactor as a pollution control device.

[citation needed] Due to American regulations, the following changes were required:[32] The optional "S Package" (320iS) was introduced in 1981 and sacrificed the factory air conditioning, but offered Recaro sport seats, upgraded suspension in the form of a rear anti-roll bar and a stiffer front anti-roll bar, a 5-speed transmission and limited-slip differential, cross-spoke alloy wheels, a larger and more extensive tool kit, a dual operation manual sunroof, an AM/FM Blaupunkt radio with cassette player, fog lights, a 3-spoke leather-wrapped steering wheel and leather shift knob, a front air dam, a "delete" of the alphanumeric 320i markers on the rear trunk lid, a central-dash storage area where A/C controls were otherwise placed, and a limited color palette of white, silver or black.

BMW Motorsport engineers simply carried out the modifications directly, with the car progressively taking its final shape.

It was also used by the BMW Junior Team, whose drivers included Manfred Winkelhock, Eddie Cheever, and Marc Surer.