1.2: BMW Motors
(by Rick Kjeldsen)
BMW's middle name is "motor", and the quality of their engines lives
up to it. Long lived, they are just getting broken in around 30k
miles, and with care easily last 200k and more. They are overdesigned
enough to take major HP modifications in stride. The performance versions,
as in the M cars, produce as much or more HP/Liter as any contemporary
(normally aspirated) production engine. They run smooth, eagerly pull
to redline and can run hard at redline all day without missing a beat.
Combine all that with a clean design which makes them a joy to work on.
The early cars (2002, early 3 series, etc) were powered by variations
on a well designed 4 cylinder block. This same basic engine has been
in use for over 25 years, and forms the basis of the very successful
E30 M3 race engines. Rumor has it that blocks for 1000+ HP Formula 1
race cars were simply selected off the manufacturing lines.
Later BMW added a large (3+ liter) in-line 6 for it's larger cars
and a small (~2.5 liter) 6 to improve the performance of it's smaller
cars. Each of these has gone through several variations over the years.
More recently BMW has built several new engines, including a V12 for
it's largest cars, V8s in a couple of sizes and a new aluminium block
2.8 liter in-line 6.
The M engines started with a major modification of the big 6 block
for the M1. It included several elements tuned for racing, including
o-rings instead of gaskets, one throttle per cylinder, etc. Later
the same technology was applied to the 4 cylinder block with a
4 valve/cylinder head to produce the E30 M3 engine.
The small-6 SOHC engine is designated the M20 series. This motor started
out in 1978 with the E21 320/6 and 323i models. As the names suggest,
the 320/6 was a 2-liter with a 4-barrel carb, and the 323i was a
2.3 liter with K-Jetronic injection.
The ETA engine, at 2.7 liters, is basically a bored and stroked version
of the 2.3 liter with Motronics, a special economy camshaft, lighter
valve springs, and a special long and small diameter runner intake
manifold. The head was basically the same as the 2.3 otherwise, with
smaller valves and ports.
The E30 325i motor is another derivation of this series of motors.
For this one, BMW shortened the stroke of the ETA engine, and used
a cylinder head with bigger ports and valves, along with a more
radical cam and stiffer valve springs (over the ETA). A larger throttle
body was also included in the package with the 323i style manifold.
The M50 engine (92-on 325i, 525i) is pretty much more or less a new
design. It is, however, based on the M20 engines.
The E30 M3 engine used the same basic block as the '84-'85 318i, and
all the other M10 4-cylinders that came before it. ('63 1500 through
the 2002 through the 320i through the early 318i) The single cam
version had a 23+ year run. The M3 version has siamesed cylinders
and a longer stroke crank, along with the 16-valve head.
The M40 engines found in the '91-on 318i's are not related to the
earlier motors in anyway.
Hope this helps,