The 325e was an economy-minded model developed for the American market. It used a stroked 2.7-litre version of the M20 engine that only produced 127hp but with a greatly improved fuel economy compared to the other six-cylinder models.
Produced for the American market, the 325e was part of BMW's answer to the 1979 oil crisis; using a high-efficiency, low-power, high-torque version of the M20 engine. Production of the 325e began in 1983 when BMW put the 2.7 litre engine from the E28 525e (known as the 528e in North America) into the E30 two-door. The first models were available to buy from early 1984. The following year, the four-door saloon version of the 325e was also released, alongside the 318i.
Built on the US-specification pre-facelift E30, it came with all the options you'd expect to see on an E30. Except high revs. The difference represented by the 'e' was in the engine bay; an engine designed with efficiency and economy at the top of the manufacturer's agenda. The little car took to it well, and more four-door 325e units were sold worldwide than the equivalent four-door 325i. It was the sports car for those who don't want a sports car.
In 1986 the 325eS was introduced. Only available in two-door coupé format, the eS was the sport model. It used exactly the same engine as the 325e, but had in addition a larger grille air inlet, sport suspension, firmer anti-roll bars, limited slip differential, sport seats, tech-1 steering wheel, rear spoiler, the 13-button OBC, Blaupunkt premium sound system, electric sunroof, and cruise control.
Despite the power shortcomings, and the car only being offered in the North American car market, and being around $2000 more expensive than the counterpart 325i, the 325e range was a massive success for BMW. In four-door saloon format, the e actually outsold the i despite the i being in production for a year longer than the e.
One of the most significant race successes for the 325e came in 1986, when tuner and driver Ray Korman was shot to fame after seven wins in one series, winning the Driver and Manufacturers Championship, and then placing 1st in the Watkins Glen 24 hour Race, using a modified version of the 325e.
The last of the 325e editions was in 1988, in the form of the vastly updated (facelift) "super-eta" cars, before production ended in late 1988, after a production run totalling around 189,287 units.
Many 325e are still around nowadays, high build-quality as well as their fundamental purpose of being driven gently, mean that they have generally lasted very well, and are still a popular car in America today. Elsewhere, they're often seen as useful donors for their engine blocks, to create the stroker. With the current social trend for more ecologically friendly cars, and the rising cost of fuel, it seems that the near future of car and engine design may lie in the past, with the E30 325e.
The 325e uses the M20B27 engine. This is the Eta engine; the 2.7 power-plant, built for economy and efficiency. The older B27 engines used the "200" head, as found in the E21 320/323i and also the E12 520. In the Eta engine, this head was modified, using only four cam bearings rather than seven, very soft valve springs, short duration cam, and small inlet manifold ports. This gave the characteristics of very low revving, and very low fuel consumption, but also very little power. The 200 Eta head was mounted on a long stroke, straight six block. This made an ideal pairing with the head, and despite the lack of power and engine speed, the long stroke produced a great deal of torque across a very wide power band.
Later cars, from 1987 onwards, were fitted with a different cylinder head. This was based on the "885" head used in the 325i, and is known as the Super Eta. To accommodate the new head, the engine management was updated to Motronic 1.3, new pistons were made, the intake manifold was made larger to match the larger ports, the rev limit/fuel shut-off was increased to 5300RPM, and the exhaust was fed through twin pipes. The compression ratio was also dropped, owing to some detonation problems when using 95RON fuel.
A common modification for the E30 is to mate the 2.7 engine block from the 325e, with the cylinder head from a 325i, thus creating a 327i. The torque of the long stroke block is combined with the high power of the uninhibited 885 head, increasing power substantially over the normal Eta engine; from 128bhp to around 185bhp, as well as some torque increase. There are a few methods for doing this modification. For details, see Building a 2.7.
Another effective, and much simpler, way to achieve more power from the Eta engine is by fitting a chip. Fuel delivery is increased, and the rev limit is raised. For more details, see the Chip Fitting Guide.