The M version of the BMW Z3 was built from
1997 to 2002 when the Z3 itself was discontinued.
(from BMW Press Release, 2002)
M Roadster and Coupe. Last year,
these two “muscle twins” among BMW sports cars were treated to the
biggest evolution since their debuts. Chief among their changes was an all new
engine, shared with the also new M3 models and endowing the roadster and
coupe with fully 75 horsepower more than the already robust 240 hp under
their long hoods.
For 2002, the M roadster and coupe continue essentially unchanged
from 2001, except that the formerly optional single-disc in-dash CD
player has been made standard. Prices are unchanged at $46,635 for the
roadster, $45,635 for the coupe, including destination charge.
These are BMW M’s huskiest, most elemental sports cars. Before
2001, they’d gained a sterling reputation as such. Yet with the dramatic new
injection of power for ’01, the raves began all over again. “Make no mistake,
the previous iteration of the M roadster was a quick pocket rocket,” wrote
Motor Trend in October 2001. “But the real story to the ’01 M roadster clearly
is its radical new S54 I-6 engine. And although a bold statement, we’ll go so
far as to say it, as well as the 333-hp version in the new M3, is the best
naturally aspirated six-cylinder we’ve ever tested. Clearly, BMW continues to
back its claim of being the ultimate driving machine.”
BRIEF OVERVIEW OF THE
2002 MODELS
Although the M roadster and coupe’s
previous engine was still earning raves in 2000, neither BMW nor BMW M
rests on its laurels. To upgrade the M models’ performance further, BMW
M created a brand-new engine, called the S54. It is essentially the same
as that powering the M3 models, except that the roadster’s and coupe’s
snug dimensions dictate a somewhat more restrictive exhaust system. The
M roadster/coupe engine delivers 315 hp and 251 lb-ft. of torque – fully
75 hp and 15 lb-ft. more than the previous engine’s output. (The M3
engine version produces 333 hp and 262 lb-ft.)
In its broad concept, the new engine,
designated the S54 1, shares the familiar basic architecture of other
BMW inline 6-cylinder engines. Virtually all of its engineering details,
however, are unique and oriented to the very highest level of
performance.
Given that other current BMW “sixes” have
an aluminum block with cast-iron cylinder liners, it may be surprising
that the new M3 engine (like its predecessor) has a cast-iron block.
Why?
Compactness is the primary reason. An
inline six is longer than a V- 6, and BMW nurtures the inline layout for
its superior smoothness and sound. An aluminum block’s cylinder liners
take up space; with liners it would not have been possible to achieve
the engine’s 3.2-liter displacement without lengthening the block.
The second reason is strength. Given that this engine develops
nearly 100 hp per liter, its internal stresses are high. According to M3 Project
Director Siegfried Friedmann, BMW engineers concluded that a cast-iron block
could best sustain the engine’s high cylinder pressures and high piston
speed at maximum rpm. The block accommodates the engine’s increased
bore and stroke of 87 x 91 mm, up from the previous U.S. engine’s 86.4 x
89.6 mm to give a displacement of 3246 cc, vs. 3152 before. Increased
displacement, however, is not the major contributor to the huge power
increase over the previous engine. More significant are the new
induction, combustion and exhaust engineering, together with the unit’s
high-rpm concept. In terms of actual hardware, the starring role here is
played by a brand-new cylinder head that could be termed “exotic.”
Feature-by-feature, the new cylinder head (of aluminum as before)
departs dramatically from the previous U.S. head, becoming more like those
of other BMW M engines. Features shared with the M5’s V-8, for example,
are noted with an asterisk (*):
Double VANOS steplessly variable valve timing*. The engine’s
Double VANOS 2 steplessly varies valve timing on the intake and exhaust
camshafts. Though this same basic VANOS system is employed in 3, Z3
and 5 Series 6-cylinder engines, as used in the S54 it varies timing over a
wider range and contributes strongly to the engine’s high power output.
Intake timing is varied by 60o, exhaust by 46 o, vs. 40 o /25 o 3 in the regular production
engines. As always, VANOS is hydraulically actuated via
electronic controls.
VANOS pressure pump*. VANOS has its own radial-piston oil pump; in
regular-production BMW engines the main oil pump supplies the pressure
for VANOS. This pump is part of the exhaust camshaft’s VANOS
mechanism, and produces up to 120 bar (1740 lb./sq in.) of pressure. The high pressure enables the system to vary valve timing more quickly at very
high rpm than would the standard system. Thus BMW M refers to the M3’s
VANOS system as High-Pressure Double VANOS*.
Unique valve mechanism. Other BMW double-overhead-camshaft
(DOHC) engines employ “bucket-type” hydraulic lifters, actuating the valves
directly with minimum noise and no periodic adjustment. For the S54’s rpm
potential, however, BMW M needed a valvetrain with less reciprocating
mass.
To achieve this, the M engineers created a new actuating mechanism,
using finger-type rocker arms. Pivoting on their own shafts (one on the intake
side, one on the exhaust), these arms reach out to form the actuating surface
between camshaft and valve. They weigh less than the bucket tappets, and
as the entire arm does not move the distance of valve lift, its effective
reciprocating mass is less than its actual mass. Altogether, the rocker arms’
effective mass is 30% less than that of the bucket tappets; in turn, this
allows lighter valve springs, which also reduce inertia. All this helps the
engine attain its 7600-rpm capability.
This mechanical system does require periodic inspection. Lead
engine engineer It is unlikely that clearance will ever actually need
adjustment, but if so it is done with shims (tiny metal discs of various
thickness) without removing the camshafts. The rocker-arm arrangement also
generates less friction.
Where the regular-production 6-cylinder engines have a simplex
(single) primary chain driving the exhaust camshaft and a smaller secondary
chain driving the intake camshaft from there, the S54 has a full duplex
(double) chain driving both camshafts directly. As usual with BMW engines,
the chain is hydraulically tensioned and needs no periodic adjustment or
replacement.
Extra-high compression ratio*. At 11.5:1, the M engine has the
highest ratio in current BMW production. (At 11.0:1, the M5 is second highest.)
Machined surfaces*. For smooth airflow the combustion chambers and
intake ports are fully machined; the exhaust ports are partially machined. For
durability, the valve seats are of especially hard steel. A 3-layer stainless steel
head gasket ensures effective sealing of the head to the block.
Head casting and sealing. Extreme strength in the cylinder head is
achieved by making it a single aluminum casting. Though more difficult to
achieve than the previous European engine’s 2-piece head casting, this
construction also saves a significant 29 lb. – at the top of the engine, helping
lower the center of gravity.
2002 M Roadster - Specifications
Curb weight, lb. 3131
Weight distribution, front/rear, @ 51.4/48.6
Wheelbase, in. 96.8 1
Track, front/rear, in. 68.5 1
Length, in. 158.5 1
Width, in. 68.5 1
Height, in. 50.1 2
Body Type Unitized
Aerodynamic drag coefficient 0.42
Engine type DOHC 24-valve inline 6-cylinder, High-Pressure Double
VANOS 4 steplessly variable intake & exhaust valve timing, 6 individual
electronically controlled throttles
Bore x stroke, mm/in. 87.0 x 91.0 / 3.43 x 3.58
Displacement, cc/cu in. 3246/198
Compression ratio 11.5:1
Power @ rpm, hp SAE net 315 @ 7400
Torque @ rpm, lb-ft. 251 @ 4900 |
