The BMW S50 straight six powered the E36 M3 and Z3 M. Here’s how the M50-based unit became a performance icon
Words: Elizabeth de Latour
After the E30 M3 and its storming S14, the car’s successor needed a suitably impressive engine. While the E36 M3 may have been met with a slightly lukewarm reception upon its launch, the S50B30 and its B32 successor were both incredibly impressive engines and a huge amount of work went into creating them. The S50B30 arrived in 1992 and remained in use until 1995, with a different variation for North America and a couple of limited production models. The S50B32 was used in the M3 3.2 Evo from 1995 to 1999 and in the Z3 M Coupe and Roadster from 1997 to 2001.
The S50 is based on its non-M M50 counterpart, with a cast-iron block but with a large number of significant revisions. The biggest M50 engine was the 2.5, but for the S50, BMW increased the bore to 86mm and stroke to 85.8mm to take capacity up to 2990cc. Compression rose to 10.8:1, and BMW M ported and polished the cylinder head while individual throttle bodies were fitted to every cylinder. Heavy-duty valve springs were fitted, along with single-Vanos, a dual-mass flywheel, free-flowing intake and exhaust system, with Bosch Motronic M3.3 engine management looking after everything.
This version of the S50B30 made 286hp at 7000rpm, with 236lb ft of torque at 3600rpm. For the US-market E36 M3, BMW developed the S50B30USA; the two engines used similar blocks and shared the same capacity, but that’s where the similarities ended. The B30USA used the less complex head and two-stage Vanos of the M50, as well as retaining hydraulic lifters. It also missed out on the individual throttle bodies and used a lower compression ratio of 10.5:1. It developed 240hp at 6000rpm with 225lb ft of torque.
The BMW M3 used the S50 in 3.0-litre form from 1992 until 1995.
There were several special versions of the S50B30 produced. For the E36 M3 GT, the engine was fitted with 264º cams, a BMW Motorsport dual-pickup oil pan, duocentric oil pumps and upgraded Vanos software, which gave it 295hp at 7000rpm and 238lb ft of torque at 3900rpm. For the Australian-only E36 M3-R, the engine was tuned by BMW M and Schnitzer Motorsport and fitted with more aggressive cams, revised intake and exhaust ports, a lightweight flywheel and a dual-pickup oil pump. These changes resulted in 324hp at 7200rpm and 258lb ft of torque at 4400rpm.
For the S50B32 (pictured in the main image above in a red engine bay), BMW M introduced several revisions to improve performance. Bore and stroke were increased to 86.4mm and 91mm for a total capacity of 3201cc, while the compression ratio rose to 11.3:1. Double-Vanos was introduced, and lightweight pistons were fitted, along with graphite-coated con-rods, larger inlet valves, improved intake and exhaust systems, an improved dual-mass flywheel, secondary oil pump pickup and BMW/Siemens MSS50 engine management. This took power to 321hp at 7400rpm, and torque now stood at 258lb ft at 3250rpm, with the S50B32 being the first road-going BMW engine to break the 100hp/litre barrier.
For the South African market, the engine was revised slightly to be able to cope with the country’s lower octane fuel. Different pistons were utilised, dropping the compression ratio to 10.5:1, and power dropped to 310hp at 7400rpm with 251lb ft of torque at 3250rpm. For the M3 Evo, the US received the S52B32, based on the M52, and capacity stood at 3152cc thanks to a bore of 86.4mm and 89.6mm stroke. The engine was fitted with more finely balanced camshafts, reduced mass valve lifters, springs and spring seats, and revised intake and exhaust systems. Despite these changes, power remained unchanged at 240hp at 6000rpm, but torque increased to 236lb ft at 3800rpm, though, in cars fitted with the automatic gearbox, torque was restricted to 225lb ft.
The S50B30 as fitted to the BMW M3 3.0
S50B30
Capacity: 2990cc
Bore: 86mm
Stroke: 85.8mm
Compression ratio: 10.8:1
Max power: 286hp @ 7000rpm
Max torque: 236lb ft @ 3600rpm
Applications: E36 M3 3.0
S50B32
Capacity: 3201cc
Bore: 86.4mm
Stroke: 91mm
Compression ratio: 11.3:1
Max power: 321hp @ 7400rpm
Max torque: 258lb ft @ 3250rpm
Applications: E36 M3, E36/7 Z3 M & Z3 M Coupe
