BMW Alpina C2
An interesting variant of the M20 engine was Alpina's C2.
The first C2 combined the wider bore of the M20B25 with the slightly larger 76.8 mm (3.02 in) crankshaft of an M20B23, to create a torquier engine of 2552 cc. This version put out 185 PS (136 kW) and 265 N·m (195 lb·ft), 74 units were built between 1985 and November 1986. After the C2 2.7 appeared in the spring of 1986, the 2.5 was slightly upgraded and gained five horsepower. However, to indicate its "little brother" position in the lineup, the name was changed to C1 2.5. When the September 1987 facelift model of the E30 was introduced, the 2.5 litre C1 was discontinued, although a few cars were finished into 1988.
The larger yet 2.7 litre unit was introduced in February 1986 in uncatalyzed C2/1 form. This engine, sharing the dimensions of the M20B27, develops a whopping 210 PS (154 kW) at 5800 rpm and shows what the engine was really capable of. Originally installed in the E30-based Alpina C2 2.7, with available four-wheel drive, the catalyzed C2/2 appeared in the interim C2 2.7 Kat in March 1987. This was then renamed "B3 2.7" five months later, by which time the "C2" labelled cars were discontinued. The B3 2.7 continued to be available until June 1992, in all body variants and drivetrain configurations (excepting automatics) in which the E30 was offered. Around 1988, 26 "B6"-labelled C2-engined E30s were built for export to Japan, where the B6 3.5 had a hard time passing emissions regulations.
Later C2 2.5 models (C2 /3 2.5) were based on the 325i. Alpina used the M20B25 engine with very few modifications compared to earlier models. Again the cylinder head was decked to increase compression ratio, and it was ported and polished. The ECU was also remapped. Max power is 140 Kw / 190 bhp, with 235 Nm of torque. 0–100 km/h was achieved in 7.2 seconds. Top speed is 220 km/h. Only 50 cars were built.
The C2 /1 2.7 used the 325e eta model engine block, crank and rods, but with custom flat head pistons provided by MAHLE. Originally Alpina modified the "200" casting number cylinder head specific to the 325e with bigger intake valves, larger air intake ports, and redesigned the valve chamber for better flow. A more aggressive camshaft was used, with higher lift and duration, and harder valve springs were installed. Compression ratio was increased to 10.2:1. The C2/1 2.7 made 210 bhp with 267 Nm of torque and was the fastest E30 available at the time (227 km/h top speed). 108 cars were built.
Later C2 /2 2.7 (and early 1987 B3 2.7) used the M20B25 block with ETA (325e) crank and rods. The intake manifold was also redesigned for better flow. The head was decked to improve compression ratio ( 10.1:1 for models with the 731 head, 9.6:1 for later "885" head models with catalytic converter ) and matched with custom pistons - flat MAHLE pistons for engines equipped with the 731 head, and domed KS pistons for engines equipped with the 885 head. Larger throttle bodies were installed (the C2/2 version uses the same throttle body as the M20B25 325i). A total of 309 cars were built between 1986 and 1987. The C2/2 2.7 makes 204 bhp and 266 Nm of torque. Top speed is 224 km/h and 0-100 kp/h is achieved in 7.5 seconds.
The B3 2.7 is similar to late C2/2 2.7 cars. It uses the M20B25 block with M20B27 crank and custom rods. The 885 head is exclusively used for the B3 model. The head is decked ~ 1mm to improve CR to 9.6:1 and matched with custom domed KS or MAHLE pistons. Intake and cylinder head are ported and polished. Custom ECU mapping is used. Engine management is Bosch Motronic 1.3. The B3 2.7 is equipped with a catalytic converter to conform to emission standard of the time. performance numbers are similar to the later C2/2 2.7 cars. 254 cars were built from 1987 to 1992.