DTM regulations required all competing cars to be slightly modified, production models, and although the motorsport division’s engineers worked wonders on the plebeian 3 Series, the model which was never designed for the track reached its limitations.
However, behind closed doors, BMW M was working on an E30-based homologation special ever since 1984. Based on a standard chassis with motorsport-derived suspension and brakes, it featured a series of aerodynamic improvements including a new front splitter, rear apron, sill panels, C-pillars, trunk lid, and rear spoiler. But the biggest improvement of them all was the new engine.
The main goal was to make the car as light as possible, so instead of using one of the company’s successful six-cylinders as the base for the new design, Roche decided to build a straight-four.
The block came from the M10, BMW’s first modern four-cylinder. Although designed in the late 1950s, the cast-iron block was so good that it was used as the base for the most powerful Formula 1 engine of all time, the turbocharged M12 which was capable of close to 1,500 hp with maximum boost.
For the cylinder head, Roche took the aluminum unit with a dual overhead camshaft (DOHC) design from the M88, another legendary mill, that he initially designed for the spectacular M1 mid-engine sportscar.
For the internals, Roche used beefy cast pistons and conrods that connected to a forged, fully counterweighed crankshaft. The compression ratio was high for a normally aspirated engine built in the 1980s. It stood at 10.8:1 in the initial 2.3-liter version, and grew all the way up to 11:1 in the larger-displacement iterations that followed.
In all versions of the S14, the cam gears were driven by dual-row timing chains that were extremely sturdy, but throughout the engine’s lifespan, BMW used different chain tensioners, some of which were prone to premature wear.
Powered by a 197-hp S14 that was linked to a Getrag 265 five-speed manual, the BMW M3 was unveiled to the public at Frankfurt Motor Show in 1985, with production kicking off several months later. It exceeded all expectations in terms of sales, and gave birth to one of the most famous high-performance sports car nameplates of all time.
On the track, the M3 made its debut in 1987, winning almost all the competitions it entered. The list of titles includes the DTM, World Touring Car Championship, European Touring Car Championship, Australian Touring Car Championship, as well as the Japanese Touring Car Championship where it would defend its crown for the following six seasons.
The biggest and most powerful S14 ever built was found under the hood of the Sport Evolution (known as Evo 3) produced in just 600 units. The engine’s displacement was enlarged to 2.5 liters by increasing the bore and stroke to 95 x 87 mm (3.74 x 3.42 in). It could produce 235 hp in road-legal guise and 374 hp in race configuration.
These revamped homologation models solidified the M3’s position as one of the most dominant cars in the history of motorsport. It continued racking up titles in various touring car championships all over the globe, and even established itself in endurance racing, winning the 24 Hours of Nürburgring five times, between 1989 and 1994.
Although the S14 was the first and last straight-four to power an M3, it’s undeniably the best four-cylinder ever created by the Bavarians, and one of the best four-cylinders of them all.
If you want to know more about this legendary engine, I highly recommend watching the video below posted on YouTube by driving 4 answers.