When the 535i was released, Alpina had become more a manufacturer than a tuner, a by-word for performance in every sense of the term, due in no small part to the continually successful efforts of Burkhard Bovensiepen and his team.
The top of the Alpina range in the late 1970's was, as usual, a BMW, based on the then new 5 series. The previous 5 series was the base for cars powered by a 3-liter turbo developing 300 hp and a 330-hp 3.5-liter unit, but the B9 was a normally aspirated 3.5-liter which developed 245 hp.
The engine was the 3453-cc overhead-cam inline six as modified by Alpina. The main change was new forged pistons with domed crowns which lifted the compression ratio from 9.3 to 10.2:1 . The rest of the work was done on the top end of the engine, with hemispherical combustion chambers and a revised camshaft, a special twin exhaust, and Bosch injection which was controlled, together with the ignition, by a Motronic computer system.
Thus modified, the power output went up from an already healthy 160 kW (218 hpj to 180 kW (245 hp). Maximum power was achieved at 5700 rpm rather than 5200 rpm, but maximum revs remained at 6000. Torque improvment was less spectacular, rising only by 10 Nm, to 320 Nm (235.8 Ib-ft). This figure was available at 4500 rpm, 500 revs higher than with the standard unit.
Alpina used BMW's high-geared "touring" five-speed box and the standard clutch, but used a 25 percent limited-slip differential. The increased power made the long box give normal performance, and top speed was achieved in fifth gear.
The braking system remained unchanged from that of the production car, but the suspension was well modified, with variable-rate springs, special Bilstein gas-filled dampers, and a three-level adjustable rear suspension.
tires were Pirelli P7s, with 205/50 VR 16s on 7-inch rims (front) and 8-inch rims shod with 225/50 VR 16s (rear). Externally, the car had front and rear spoilers and an Alpina color scheme, while the interior was trimmed to the usual Alpina standards and was equipped with special bucket seats.
The modifications endowed the 1390-kg (3064-lb) car with a top speed of over 240 km/h (150 mph) and a 0 to 100 km/h (62 mph) time of 6.7 sec. Standing 400- metre and kilometre times were 15.3 and 27.7 seconds respectively, giving the B9 performance in the same class as a 928 Porsche, despite the fact that it was 70 kg (154 Ib) heavier than the standard 528i.
