In This ArticleEarlier than turbocharging took over, earlier than variable valve timing grew to become customary, and earlier than BMW’s M division had something near a quantity playbook, there was the S38. A naturally aspirated inline-six of near-surgical precision, the S38 powered the unique M5 and M635CSi by among the most celebrated years in efficiency automotive historical past. It was — and in some ways nonetheless is — the whole lot a driver’s engine needs to be.
That is the definitive information to the BMW S38: the place it got here from, the way it works, what it’s wish to personal, and what it might probably do with slightly encouragement.
Origins: From Racetrack to Street
The S38 doesn’t exist with out the M88. Within the late Nineteen Seventies, BMW Motorsport developed the M88 — a 3.5-liter inline-six with a twin-cam, 24-valve head — to energy the BMW M1 supercar. That engine produced round 277 hp in street trim and was thought-about state-of-the-art for its time. When the M1 undertaking wound down, BMW Motorsport had a rare engine on their palms and no new house for it.
The reply got here within the type of the E28 M5, unveiled on the 1984 Amsterdam Motor Present. To place this in context: the M5 was, at launch, the quickest manufacturing sedan on the planet. Underneath the hood sat the S38B35, a direct evolution of the M88 tuned for street use. It retained the six particular person throttle our bodies and hand-built meeting course of, however was tailored for daily-driving calls for — higher drivability at low revs, up to date gas injection, and emissions compliance.
When the E34 M5 arrived in 1988, the S38 developed additional. The engine was revised and ultimately enlarged to three.8 liters in 1992, giving the S38 its strongest road-going kind. All through its manufacturing life, from 1984 to 1995, the S38 remained a cornerstone of BMW M’s engineering id.
Technical Specs
The S38 is a naturally aspirated, DOHC inline-six with 4 valves per cylinder and 6 particular person throttle our bodies — one per cylinder. Development is all-aluminum with a cast-iron block on early variants, and the engine was assembled largely by hand at BMW’s Garching facility. There aren’t any hydraulic lifters; valve clearances are set mechanically, and the engine rewards correct upkeep with extraordinary longevity.
S38B35 (1984–1991)
- Displacement: 3,453 cc
- Configuration: Inline-6, DOHC, 24-valve
- Bore × Stroke: 93.4 mm × 84.0 mm
- Compression Ratio: 9.8:1
- Energy Output: 286 hp (210 kW) @ 6,500 rpm
- Torque: 251 lb-ft (340 Nm) @ 4,500 rpm
- Gasoline System: Bosch Motronic ML31.1
- Redline: 7,000 rpm
- Functions: E28 M5, E24 M635CSi
S38B38 (1992–1995)
- Displacement: 3,795 cc
- Configuration: Inline-6, DOHC, 24-valve
- Bore × Stroke: 94.6 mm × 90.0 mm
- Compression Ratio: 10.0:1
- Energy Output: 340 hp (250 kW) @ 6,900 rpm (Euro)
- Torque: 295 lb-ft (400 Nm) @ 4,750 rpm
- Gasoline System: Bosch Motronic 3.3
- Redline: 7,200 rpm
- Functions: E34 M5 (from 1992 MY)
Notice: North American-spec E34 M5 fashions obtained a detuned S38B38 rated at 310 hp as a result of emissions compliance necessities.
Engine Variants
S38B35 — The unique. Fitted to the E28 M5 from 1984 and the E24 M635CSi, this 3.5-liter unit set the template. The early E34 M5 (1988–1991) additionally used a developed model of the B35, producing 315 hp in European specification because of revised camshaft profiles and up to date Motronic administration. Whereas the displacement designation is similar, the E34’s iteration is meaningfully totally different in tune and character.
S38B38 — The definitive model. Launched for the 1992 mannequin yr E34 M5, the B38 stretched bore and stroke to succeed in 3,795 cc. Energy climbed to 340 hp in European kind — an infinite determine for a naturally aspirated road engine within the early Nineties. This was additionally the model supplied to North American consumers, although with emissions tools that decreased output to 310 hp.
The Automobiles It Powered
E28 M5 (1984–1988): The automotive that began all of it. Inbuilt restricted numbers on the Garching M facility, the E28 M5 was basically a homologation train that grew to become a legend. With the S38B35 underneath the hood, it was the world’s quickest manufacturing sedan at launch. At this time it’s one of the vital collectible BMWs ever made.
E24 M635CSi / M6 (1984–1989): The grand tourer variant. The M635CSi (bought because the M6 in North America) paired the S38B35 with an extended wheelbase and extra luxurious cabin. It’s arguably essentially the most lovely utility of the engine — a driver’s automotive wrapped in a touring-car physique.
E34 M5 (1988–1995): The longest-running and most refined S38 utility. The E34 M5 is extensively thought to be essentially the most well-rounded M automotive of its period — combining real supercar efficiency with a sensible five-door physique (in Touring kind in choose European markets) and a cabin that might move for a luxurious saloon.
Reliability and Widespread Points
The S38 has earned a powerful status for sturdiness — when maintained correctly. These engines have been constructed to be serviced, not thrown away, they usually reply accordingly to attentive possession.
Valve clearances: That is the one most essential upkeep merchandise on any S38. The engine makes use of mechanical (shim-and-bucket) valve adjustment. Clearances have to be checked each 30,000 miles or so, and if uncared for, the implications vary from poor operating to valve practice harm. It’s a labor-intensive job however not a troublesome one for a certified BMW specialist.
Oil leaks: Anticipate them on any high-mileage instance. The valve cowl gasket is the commonest offender, adopted by the oil pan gasket and the entrance and rear foremost seals. None of those are catastrophic points, however they need to be addressed after they seem to forestall oil contamination of belts and electrical elements.
Throttle physique synchronization: Six particular person throttle our bodies have to be balanced for the engine to idle cleanly and pull evenly. This requires correct tooling (a manometer or related vacuum balancing software) and is finest performed by somebody conversant in the engine. A poorly synced S38 will really feel flat within the mid-range and should idle erratically.
Cooling system: The water pump is pushed by the cambelt on the S38B35 and is a vital service merchandise. Failure of the water pump or thermostat on a high-mileage engine could cause severe overheating harm. Exchange each elements as preventive upkeep throughout any main service.
Timing belt: In contrast to lots of its contemporaries, the S38 makes use of a timing belt quite than a sequence. The service interval is 30,000–40,000 miles, and this needs to be handled as non-negotiable. A snapped belt on an S38 is an interference occasion — that means important engine harm follows.
Vacuum traces: The engine’s age means unique vacuum traces have typically deteriorated. Perished hoses trigger tough idling, poor vacuum brake help, and inconsistent throttle response. A full vacuum line refresh is reasonable insurance coverage on any high-mileage automotive.
Upkeep Ideas
- All the time use a high-quality totally artificial 10W-60 oil, and alter it on a 5,000-mile interval or yearly, whichever comes first. The S38 runs scorching by fashionable requirements and advantages from premium lubrication.
- Discover a specialist conversant in the engine earlier than shopping for. Pre-purchase inspections ought to particularly embrace a compression take a look at, leak-down take a look at, and a pay attention for timing belt rattle at chilly begin.
- Coolant flushes each two years are worthwhile no matter mileage. The aluminum elements within the cooling system are delicate to degraded coolant chemistry.
- Maintain data of valve clearance checks. A documented service historical past on an S38 is value significantly greater than an undocumented automotive.
Tuning Potential
The S38 was not designed with aggressive aftermarket tuning in thoughts — it was already close to the bounds of what naturally aspirated growth might obtain in interval. That stated, significant energy good points are doable with the best method.
ECU remapping is essentially the most accessible route on the B38. Fashionable standalone ECU options (or mapped Motronic replacements) can optimize ignition timing, gas supply, and rev restrict, usually yielding 15–25 extra horsepower on an in any other case inventory engine.
Camshaft upgrades can be found from a small variety of specialist suppliers and may meaningfully enhance top-end energy at the price of some low-rpm tractability. This fits monitor use higher than on a regular basis driving.
Throttle physique porting and sprucing, mixed with high-flow particular person throttle our bodies from specialist suppliers, is a well-liked route on devoted monitor automobiles. Paired with a free-flowing exhaust and ECU work, a well-built S38B38 can attain 370–385 hp whereas remaining naturally aspirated.
Compelled induction is technically doable however hardly ever tried, partly as a result of the engine was not designed for enhance and partly as a result of the automobiles it powers are actually too worthwhile to change radically. The few turbocharged S38 builds that exist are severe engineering undertakings.
The sincere reality is that the majority S38 homeowners don’t tune their engines — and this is smart. The inventory energy supply is so characterful and so well-matched to the automotive’s chassis and gearing that chasing numbers dangers dropping what makes the engine particular.
Legacy
The S38 represents the tip of a specific period in BMW M historical past: the period of hand-assembled, naturally aspirated engines inbuilt small numbers by craftsmen who signed their work. Each S38 that left Garching bore the signature of the technician who assembled it — a element that appears nearly quaint in the present day, however speaks to how these automobiles have been conceived.
Later M engines could be sooner, extra technologically subtle, and extra dependable. The S54 that adopted within the E46 M3 is rightly celebrated. The present S58 is an engineering masterpiece. However none of them appears like an S38 at full chat, and none of them fairly captures the sense that you just’re working one thing that was made, quite than manufactured.
For that cause, the S38 retains a loyal following that reveals no signal of diminishing. If something, because the automobiles it powered climb in collector worth, appreciation for the engine itself has grown proportionally. It’s — as its lineage from the M1 would counsel — a real piece of automotive historical past.
In search of a used BMW S38-powered automotive? All the time prioritize documented service historical past, a verified valve clearance test, and contemporary timing belt. The automobiles are sufficiently old now that deferred upkeep is the first threat — however discover a well-kept instance and also you’ll have one thing actually irreplaceable.
