S5x

The BMW S5x range of engines are a line of 6-cylinder engines, fitted to BMW Motorsport models between 1992 and 2001. The range is comprised of three main units; the S50, the S52 and the S54. All S5x engines are fundamentally based on the M5x series of engines that powered the E34 M5 and E36 M3, and are one of the most powerful (and challenging) engine swaps.

A lot of confusion exists online due to BMW's idea of releasing two different engines called the S50; one for the US and one for the rest of the world. Hopefully this will clear a few things up.

Versions

S50

The S50 engine first saw action under the bonnet of the E36 M3 as a 3.0 engine. These phenomenal units were complete rebuilds of the iron-block M50 engines; the blocks had a wider bore, the crank had a longer stroke and the whole compression was raised to 10.8:1. Compared to the simple 24V head of the M50, these engines featured VANOS technology and independent throttle bodies (six in all) for improved top-end performance.

In 1995 they went through an upgrade, with an increased bore and stroke taking displacement to 3.2 litres. To cope this this, the heads were fitted with Double VANOS to regulate both the intake and exhaust valves, and a second oil pump fitted. Seeing active duty in the E36, these bigger lumps were also stuffed into the Z3 M Coupe and Roadster.

S50 engines weigh 151kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
S50B30	3.0 L (2990 cc/182 in³)	210 kW (282 hp) @ 7000	320 N·m (236 ft·lbf) @ 3600	7200	86mm	86mm	1992
S50B32	3.2 L (3201 cc/195 in³)	236 kW (321 hp) @ 7400	350 N·m (258 ft·lbf) @ 3250	7600	86.4mm	91mm	1995

S50US

Unfortunately for the US market, the phenomenal performance of the S50 engine came at too high a cost, both in dollars and pollution. To import such an engine and tune it to meet stringent emissions regulations would put a standard M3 far above the price bracket at which it was marketed.

Rather than rebuilding the S50, BMW adapted the existing M50 design to offer a tuned engine that performance half way between. Power and torque output are significantly decreased in contrast to the "original" S50, but are a massive improvement on the M5x design. At 240hp, the S50B30US slots neatly between the M50B25 at 191hp, and the S50B30 at 282hp.

This S50B30US is a strange beast. It features a VANOS head, but not the same VANOS system as the "genuine" S50 - it's stepped rather than variable - and also hasn't undergone the significant porting and polishing required to get the best gas flows. Most importantly, it lacks the independent throttle bodies found on every Motorsport engine since the M1 back in 1978.

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
S50B30US	3.0 L (2990 cc/182 in³)	177 kW (241 hp) @ 6000	305 N·m (225 ft·lbf) @ 4250	6500	86mm	85.8mm	1994

S52

Rather than develop their S50 further, in 1996 BMW adopted the S52 unit for the American market, which is based on the existing M52 engine. Because of that, they have the iron block the US used for those motors, rather than the lighter aluminium version used in Europe.

These engines were bored out similar to the S30B32, but retained the power output of the original S50US engine of 240hp. However, the increased stroke of the engine increased the maximum torque while flattening the torque curve, meaning you get more from the engine at lower revs.

S52 engines weigh 141kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
S52B32	3.2 L (3192 cc/195 in³)	177 kW (241 hp) @ 6000	320 N·m (236 ft·lbf) @ 3800	6500	86.4mm	89.6mm	1996

S54

Eventually all this nonsense about Euro v US engines was sorted out with the introduction of the S54. By returning to the original M50 design, BMW were able to use the full potential of the 3.2 litre displacement to eke out a massive 343hp, with only the smallest dilution down to 333hp for the US market.

These engines increased the bore of the original S30B32 even further and raised compression to 11.5:1, in order to squeeze every last pony from the design. The success of the experiment was seen with the launch of the E46 M3 in 2001. A detuned version was fitted to the Z3 M versions, presumably limited to stop it tearing the car apart, before returning to full-fat flavour for the Z4. A special 355hp variant was produced exclusively for the 2004 E46 M3 CSL.

S54 engines weigh 148.5kg

Engine	Displacement	Power	Torque	Redline	Bore	Stroke	Year
S54B32	3.2 L (3246 cc/198 in³)	256 kW (343 hp) @ 7900	365 N·m (269 ft·lbf) @ 4900	8000	87mm	91mm	2001