BMW M88 and S38 M-Tech 24 Valve Six Cylinder Engines

BMW S38 engine

M88 in the back of an E26 M1 super car.


BMW had used a heavily modified 12 valve M30 in their E9 3.0CSL racing cars of the early 70's, it was called the M49. It started as a 3.0 but grew to a 3.3 and there was even a (literally) fire breathing turbo version. For the late 70's E26 M1 super car that they were building in partnership with Lamborghini a 24 valve follow on from the M49 was specified. This new engine was to be called the M88.

The M88 saw service in the M1 from 1978 until 1981. It proved to be reliable and easy to live with. This was a vastly different story from most 70's super cars which needed constant fettling and broke down frequently. This pattern of high performance yet comparatively low maintenance needs was to set the pattern for the BMW Motorsport engines which succeeded it.

The Motorsport division had toyed with the E12 five series in the late 70s by building several low production M30 based cars culminating in the M535i with its M30 3.5. But for the follow on E28 five there was not only to be another M30 based M535i but a super saloon with an updated M88 24 valve engine. The first M5 was unleashed on the market in 1985 to rave reviews and sold until 1987. The same engine was sold in the E24 M635CSi from 1983. The US version had the shorter name of M6 and produced around 260 bhp instead of 286 due to its catalytic converter.

The E23 745i used a turbocharged M30, but BMW South Africa built their own version with an M88 and the same 745i badge.

Around this time BMW changed their engine numbering system and the M88 retrospectively became the S38.

In 1988 the E34 five series was launched, it's 535i model won well deserved "Car of the Year" awards in many countries. In terms of comfort and build quality it was a leap forward from the E28 but this also made it heavier. So for the E34 M5 the S38 would need more power, a 3.6 with an extra 30 bhp was duly created. The final E34 M5s had a 3.8 litre S38 delivering 341bhp.

The S38 captures the real spirit of BMW. A race bred mechanical work of art not reliant on forced induction to produce power. An engine capable of decades and hundreds of thousands of miles of effort without major work. This is why //M cars are set on a pedestal. This generation of engines set the bar high for those that came after.

BMW S38 engine

S38 in an E45 M5 showing the newer air box and MAF.


The M88 had four valves per cylinder and a modified 3.5 litre block from the M06 (M30) engine. The cylinder head comprised of two layers of aluminium castings and a cast valve cover. The lower section of the head held the valve guides, water passages and mated with the cylinder block. The upper section held the camshafts. A double row chain was used to drive the twin cams which operated the valves by means of bucket type tappets. These tappets were not hydraulic or adjustable, the clearances were set by shims.

Fuel injection was performed by a mechanical Kugelfischer system similar to that used on the 2002tii. There were six individual throttle bodies to improve airflow, these were fed by short intake trumpets which joined to a large air box - there was no intake manifold as such.

The M1 was never homologated for Group 4 racing as had been the goal. Instead a highly successful one make Procar race series was staged before Formula 1 races. M88 racing engines for this series made around 480bhp thanks to larger valves, camshafts designed for use at higher revs and a much higher idle speed, forged pistons and a slide throttle in place of the individual throttle bodies. One of the hardest tasks in developing the earlier racing 3.0CSL was that of producing a strong and well balanced crankshaft capable of running at very high revs in the long six cylinder engine, this work paid dividends now.

For use in Group 5 racing the output was raised to almost 950bhp by the fitting of twin turbos and further optimisations to support forced induction.

But sadly the M1's day came to an end, the M88 was now needed for the E24 M635CSi and E28 M5. In these cars a single row timing chain was used and more modern Bosch Motronic injection was fitted. This raised power to 286bhp and greatly increased economy. In some markets it's thought that these engines were chipped down a fair bit, to as little as 240bhp. The reasons are unclear, in fact it could be the case that an M635CSi was sold at full power and the M5 at a lower level - or vice versa! The American version had lower compression and a catalytic converter, it only made 260bhp.

The M1's exhaust manifold had been fairly straight at the engine end in order to move the hot exhaust pipes as far from the engine as possible before turning. Heat was an issue in a mid engined car. This was not the case for the front engined road cars which had more conventional tubular manifolds.

The 1988 E4 M5's engine was now known as the S38 and it's initial version was a 3.6 litre. There was a new air box with a variable length runner system which was a precursor to the DISA system later fitted to non-M engines. These engines had dual row timing chains and a new upwards facing oil filter canister which was much easier to access. A MAF replaced the air flow meter and gave lower intake restriction.

All S38s now had a catalytic converter yet power increases had been found by means of higher valve lift from redesigned camshafts, tuned intake system, improved exhaust manifold and redesigned valve ports.

For the final 3.8 litre S38 BMW fitted one coil per cylinder and abandoned the distributor. This system was pioneered on the M42 in 1989. This engine had pistons of a different design and had it's variable length intake system was controlled by a revised Bosch Motronic DME instead of a separate unit.

The exhaust manifold on the 3.8 was made from Inconel. This lightweight material is very strong and hard to work, it's very expensive and normally reserved for high end racing cars such as Formula 1. The catalytic converters on this engine are different from the 3.6, they're more compact and flow better.

I believe the 3.8 went to a dual mass flywheel, a step that seems miss-guided.

BMW S38 engine

M88 in an E28 M5.


Code Size Power
Made Bore x
Timing Weight
VANOS Used in
M88 3.5 277 @ 6500

286 @ 6500

238 @ 5000

245 @ 4500





79 - 80

86 - 90

93.2x83.8 Chain 146 No M1, E23 745i

E28 M5, M636CSi

S38 3.6


315 @ 6900

340 @ 6900

260 @ 4750

289 @ 4500





88 - 91

92 - 96

Chain 151 No E34 M5


BMW S38 engine

M88 showing its six throttle bodies.


These engines used shims of variable thicknesses to set the valve clearances, a task which must be performed periodically. When the clearances are set you need a supply of these shims, this very much limits the number of garages that can do the work.

Whilst well made and robust these are complex beasts. A mechanic who's used to working on them will perform a much better job in much less time. It's worth seeking out an old hand who knows them well.

You'll hear many stories about the merits of single vs dual row timing chains and if / when they should be replaced. I'll not add my own as I'm in no way experienced enough with the S38 to do so. But I will say that generally with BMW chains if you hear any rattling you need to act, if it's quiet all is likely well. The E34 M5's S38 is regarded as more durable than the older versions in this regard as it's dual row. There were many designs of tensioner over the years and that would be the first thing to check or upgrade.

On Motronic engines the distributor and rotor arm must be in good condition as these are vital to correct ignition timing, there is no vacuum advance or similar mechanism. A worn set can cause poor economy and a lack of high end power.

You must change the coolant regularly and maintain the efficiency of the cooling system. The heads have been known to crack if overheated.

If looked after these engines will do insane mileages, there many out there with over 300,000 miles.