This site bears his name, so he should go first: the S14, the four-cylinder engine of the BMW M3 E30. It was not born on a marketing department’s drawing board, but out of a set of regulations — Group A required 5,000 road-legal vehicles within twelve months (BMW PressClub). What BMW built from this became the most successful touring car of its era and one of the most enduring legends of the brand.
Why four cylinders?
BMW states the reasons itself: low weight and high revving ability. The longer crankshaft of a six-cylinder begins to vibrate earlier at high revs — the short four-cylinder handles engine speed better by design. The block comes from series production (referred to in the literature as M10; BMW itself only speaks of a “crankcase from series production”). Added to this are two overhead camshafts driven by a duplex chain, four valves per cylinder, individual throttle bodies and a Bosch Motronic.
The origin story — told correctly
The cylinder head is derived from the M88 six-cylinder of the M1. This was made possible by the shared cylinder spacing of 100 millimetres. Engine guru Paul Rosche described the first prototype on bmw-m.com as follows: “We went and cut two combustion chambers off the four-valve cylinder head of the M88 and screwed a plate over the hole at the back” — in other words, two combustion chambers were literally sawn off the M88 head and the hole was sealed with a plate.
This is exactly where the story is usually shortened: the sawn-off M88 head was the prototype, not the production specification. The later production heads were their own design, based on the combustion chamber and valve concept of the M88. One more contradiction should be noted: the English Wikipedia traces the head back to the S38 — BMW’s own sources (PressClub, bmw-m.com with the Rosche quote) unanimously cite the M88. We follow BMW.
All versions at a glance
| Version | Displacement | Output |
|---|---|---|
| S14B23 (M3, cat) | 2,302 cm³ | 195 PS at 6,750/min |
| S14B23 (M3, no cat) | 2,302 cm³ | 200 PS at 6,750/min · 240 Nm |
| M3 from 09/1989 (cat) | 2,302 cm³ | 215 PS at 6,750/min |
| Evolution II | 2,302 cm³ | 220 PS at 6,750/min |
| Sport Evolution (S14B25) | 2,467 cm³ | 238 PS at 7,000/min |
| 320is (S14B20) | 1,990 cm³ | 192 PS at 6,900/min |
Compression ratio in the series was 10.5:1, while the Sport Evolution displacement rose to 2,467 cm³. The small S14B20 with just under two litres was developed for Italy and Portugal — we tell the whole story in a separate article on the 320is.
A number that isn’t one
BMW press texts mention 10,000/min. This describes the load capacity of the crank assembly on the test bench — not the rev limit of the production engine. Anyone citing this figure as a limit has fallen for one of the most persistent S14 legends. In total, 17,970 M3 of the E30 model line were built by the end of 1991, plus 786 Convertibles and the limited runs of Evolution (505), Evolution II (500) and Sport Evolution (600).
Sources: BMW PressClub (“20 Jahre BMW M3”, “Der BMW M3 wird 25”, “30 Jahre BMW M3”), bmw-m.com (Legendäre Motoren, Rosche quote), BMW Group Classic, Wikipedia (DE/EN). Photo: Beemwej (CC BY-SA 3.0), Wikimedia Commons.
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