BMW S50 S52 and S54 M-Tech Engines

E46 M3 CSL with an S54 3.2, perfect.

Chronology

BMW had built a legend, the E30 M3 with it's wonderful race bred S14 engine. But with the launch of the new E36 three series a new //M car was required. It was logical that it's engine be based on the M50 24 valve engine from the E36 325i.

So it came to pass that in 1993 the new M3 launched with a three litre 24 valve engine which would be the basis of M3 engines for over a decade. One wonders if it was just by chance that the S50 made 286bhp, the same figure at the S38B35 six cylinder 24 valve unit from the original M5 and M6.

The new engine wasn't capable of meeting US emissions legislation so the for the US market a toned down engine with a single throttle body in place of the six individual bodies of the Euro unit was produced. This made 240bhp and was by no means second best in real world driving.

In 1994 a limited edition M3 GT with 295bhp was sold using a slightly tuned S50B30.

In 1995 the S50B30 was replaced by the 3.2 litre S50B32 with 321bhp, this came at the same time as the M50 was replaced by the M52. At the time several magazines said this was due to the gap between the new 328i and the S50 M3 being too small.

As with the S50 the American S52 used a single throttle body. Power was unchanged but torque increased by 7% and mid-range power delivery improved. The S52 designation was only for the US engine.

By now the S50B32 was also being used in the Z3's //M-Roadster and //M-Coupe derivatives, power figures were very slightly lower due to exhaust routing.

For the new Millenium there was a new E46 M3, yet again more power was needed. Whilst early E46s used the M52TU engine by 2001 the M54 had replaced it and had it's own 231bhp three litre version. Surprisingly the new Motorsport S54 engine was based on the M50's iron block. It made 22bhp more than it's predecessor for a total of 343, much of it by virtue of a higher rev limit.

In it's ultimate E46 M3 CSL version the S54 made 360bhp. It continued until the launch of the E90 M3 with it's V8 engine.

 

American 1997 E36 M3, my mate Ed's car.

Design

The basis for the S50 was the M50TU 24 valve six cylinder, and a good basis it was. Both engines had an alloy head and iron block. The S50 had a longer stroke so it's block was 6mm taller. It used a two part cylinder head design that mimicked the S14 / S38 and in the same vein used shims to adjust the valves instead of hydraulic tappets. Of course the other major change from the M50 was the fitting of six individual throttle bodies with their associated plastic intake trumpets.

Ignition was provided by one coil per cylinder and a MAF was used to measure airflow. VANOS was provided on the intake camshaft, the single row timing chain went from the crank to the exhaust camshaft whilst a second chain linked the two camshafts. High flow catalytic converters were by now standard equipment.

The US version was basically a three litre M50TU with a single throttle body. It was a great engine, but it's technology was less exotic than it's European cousin. Many have since argued that for an everyday road car the US engine was superior, I've been in one and it certainly didn't disappoint. But was the M3 meant as an every day road car or was its purpose to be a bit more special? I think another interesting question would be how it would have faired if sold in Europe alongside the M3, the Alpina B6 2.8 and B3 3.0 offer a fair comparison perhaps. All were great cars. The later US 3.2 was based on the M52.

 

S54 3.2 cautaway drawing.

For the S50B32 displacement rose to 3.2 litres and double VANOS was introduced, early VANOS units were made by Rolls Royce and later ones by Sachs. The DME was now made by Siemens instead of Bosch, it controlled the VANOS unlike the older unit which had a dedicated module for that task.

The oil system used a double pickup point to minimise the risk of oil starvation under hard cornering. Compression was 11.3:1, up from 10.8:1 on the three litre. This was still an iron block motor, not aluminium like the M52.

The S54 was an evolution of the S50B32 (still iron block) but in practice many components were redesigned. The two part cylinder head was now one piece to save weight. The valve train used finger followers rather than direct bucket operation and the whole valve train and valves were lighter. The VANOS system was of a new design and operated more quickly than before. A scavenging oil pump was fitted to ensure lubrication under hard cornering. The compression ratio was further increased to 11.5:1 and although both are classed as a 3.2 the S54 has an extra 45cc giving 3246cc.

The E46 M3 CSL had a hotter S54B32HP with 17bhp more. In addition to the sexy carbon air box with revised flow there was a lighter and freer flowing exhaust manifold, modified exhaust valves, revised camshaft timing and cam profiles.

These were the last normally aspirated inline M-Tech engines, and that is nothing short of a bloody disgrace. Anyone can bolt on a turbo and make lots of power.

 

S50 3.0 in an E30, a perfectly sensible idea!

Variants

Code	Size	Power bhp@rpm	Torque lb/ft@rpm	BHP/ litre	Torque/ litre	Made	Bore x Stroke	Timing	Weight (kg)	VANOS
S50 Euro S50 USA	3.0	286 @ 7000 240 @ 6000	236 @ 3600 225 @ 4250	95 80	79 75	92 - 95	86x86 86.5x86	Chain	152	Single
S50B32 S52 USA	3.2	321 @ 7400 240 @ 6000	258 @ 3250 240 @ 3800	100 75	81 75	96 - 2000	86.4x91 86.4x89.6	Chain	152	Double
S54	3.2	343 @ 7900	269 @ 4900	107.2	84.1	2001 - 2006	87x86.4	Chain	217	Double

 

S54 3.2 in all it's glory.

Problems

The valve clearances on the S50 are set by shims and must be periodically adjusted. If it ticks too much as idle once warm this may be why.

Any kind of oil starvation is going to end in tears, check the level often and use decent stuff.

You'll get the usual vacuum leaks as air hoses get older and crack, not a big deal.

Using one of these as a town car with lots of short journeys is not clever. If you get one of these stick a bottle of Redex / Techron into a quarter tank of petrol then go and drive drive it like you stole it. After that do an oil flush and change. The engine will thank you.

It's more of a problem on the US cars but the radiators don't seem to last well. The plastic gets brittle with age.

Don't worry too much if it sounds a bit agricultural at idle, it wasn't designed with idling in mind.

The biggie - the Vanos on the S50B32. These use different components than the M52 / M54. Early VANOS units were made by Rolls Royce and are regarded as better than the later Sachs units. But they can all fail, the oil seals stop being oil seals and with 100bar (1400psi) of pressure that's a problem. Symptoms include a loss of power and an engine that sounds like a bag of nails. If you have a dodgy one Google "Mr. Vanos", he's the expert - but try a new VANOS oil filter and solenoid gaskets first.

Because worn VANOS units cause so much vibration the bolts holding the solenoids can shear. This can cause oil to stream out of the engine at 100bar and cause terminal damage if not stopped immediately. It's sensible to check the bolts periodically and even replace them, they're only 25 quid and easily accessible.

If the idle is dreadful and there are VANOS issues it's a reasonable DIY job to strip the solenoids and replace the piston seals, this really can make a difference.

The idle control valves seem to clog up more often on these cars than other BMWs, possibly heat related or due to more oil in the crankcase ventilation system.

There's a tiny oil filter screen in the VANOS unit, I'd be inclined to replaced it every oil service.

Early S54s had a problem with bearing shells, BMW replaced a fair few under warranty.

Don't be frightened of one of these unless it's been badly neglected. They're strong units and really are The Right Thing. Anyone who needs more power isn't trying hard enough.