OVERVIEW
The SLX is powered by an all new, lightweight 3.5 liter,
all-aluminum, double-overhead-camshaft V-6 engine which
produces 215
horsepower at 5400 rpm, and 230 lbs-ft of torque at a low 3000
rpm
providing 13% more horsepower and an incredible 22% more
torque than
the previous 3.2-liter engine. A new variable induction system
combines with four-valve-per-cylinder combustion chambers to
help
provide both high torque at low rpm and excellent breathing at
higher
engine speeds. Electronic fuel injection compensates for varying
driving and atmospheric conditions, and provides enhanced
driveability in both on- and off-highway operation. To reduce
maintenance costs, the new engine can run 100,000 miles
before its
first tune-up.
The engine is located longitudinally, moving weight to the rear for optimum handling. The standard 4-speed, electronically controlled automatic transmission is bolted as a unit to the new Torque-On-Demand 2-speed transfer case, increasing rigidity while reducing noise and vibration. The Torque-On-Demand 4-wheel drive system is engaged with the touch of a button and automatically reproportions driving force between the front and rear axles for maximum efficiency. For improved response and economy, the transmission features converter lockup in 2nd, 3rd and 4th gears.
The Acura SLX is rated with a 5000-lb (Class III) towing capacity, assuming the use of approved load-compensating trailer hitch and trailer brakes.
ENGINE BLOCK/PISTONS
The block of the new SLX engine is an aluminum casting with
cast-in
iron liners, a design known for its light weight, excellent rigidity
and good long-term durability. The crankcase is designed with a
deep
skirt and extensive webbing for added rigidity, reduced noise and
reduced vibration. To further increase engine block rigidity, a new
cast aluminum crankcase/steel oil pan assembly is applied. The
cylinder banks are set 75 degrees apart; bore centers are 102
mm
apart. The larger 3.5-liter SLX engine is an oversquare design,
with
a bore of 93.4 mm and a stroke of 85.0 mm (an increase of 8
mm.) To
reduce internal engine friction the pistons feature a short skirt
design and utilize a new piston ring design.
CYLINDER HEAD/VALVETRAIN
The SLX engine features a new double-overhead camshaft,
4-valve-per-cylinder valvetrain with pent-roof combustion
chambers.
The valves are positioned at a very narrow 19? included valve
angle
to yield straighter intake ports for better flow and a more compact
combustion chamber with a generous squish band for improved
combustion, especially at low rpms. To ensure precise valve
timing
and quiet operation, the double-overhead cams are driven by a
toothed
drive belt which drives a reduction gear mounted in each cylinder
head, which in turn drives the intake and exhaust camshafts via
special anti-backlash gears. The camshafts hold the intake and
exhaust valves open longer, and the lobe surfaces feature an
ultra-fine finish to reduce friction. The valves are now actuated
through a shim and buckle tappet configuration for lighter weight,
reduced friction and higher performance. The oversquare
bore/stroke
ratio allows for large intake and exhaust valves which improve
engine
breathing and increased power output. The cylinder heads are
aluminum
castings while the valve covers are now made of lightweight cast
magnesium.
VARIABLE INDUCTION SYSTEM/AIR INTAKE
To help generate maximum horsepower and torque over a broad
powerband, the 1998 SLX features a variable induction system.
To take
maximum advantage of the intertial "ram effect" of the incoming
fuel/
air charge, the intake manifold uses long intake runners
connected to
a large plenum chamber at engine speeds below 3600 rpm.
Above 3600
rpm, a electronic solenoid opens a butterfly valve revealing a
short
direct intake path for improved high rpm power. To help ensure
that
the engine is receiving cool, dense air, the air intake has been
relocated from the engine compartment to inside the left front
fender.
ELECTRONIC FUEL INJECTION
To help ensure optimum fuel injection performance for improved
power
and economy, fuel is metered by the Powertrain Control Module
(PCM),
based on data received from sensors that measure intake
vacuum, air
mass, throttle valve position, coolant temperature and engine
rpm.
Fuel is maintained at a constant pressure in the fuel rails above
each cylinder bank; the PCM regulates fuel delivery by varying the
opening time of each cylinder's individual injector.
ELECTRONIC ENGINE MANAGEMENT
A sophisticated Powertrain Control Module (PCM) controls and
coordinates all engine and transmission functions, resulting in
increased performance, enhanced reliability, smoother shifting
and
reduced emissions. For improved acceleration under full throttle,
the
PCM automatically disengages the air conditioning compressor.
Under
moderate acceleration, the PCM also reduces alternator drag by
reducing ampere output by 50%; if the headlights are on, the
PCM lets
charging continue uninterrupted.
STAINLESS STEEL EXHAUST SYSTEM
A highly efficient stainless steel exhaust system is used for
excellent performance and enhanced durability in difficult driving
conditions. The system uses 2 large catalytic converters, giving
quicker light-off, better flow characteristics, improved component
protection and better packaging efficiency than a more
conventional
single-converter design.
IGNITION SYSTEM
The PCM precisely controls ignition timing by monitoring a
crankshaft
angle sensor mounted in the engine block. A direct ignition
system
with six individual ignition coils is used, each providing a 33,000
volt spark to help ensure complete combustion. Platinum tipped
spark
plugs are now fitted to the SLX and do not require replacement
for
100,000 miles.
4-SPEED AUTOMATIC TRANSMISSION
Every Acura SLX is equipped with an electronically controlled
4-speed
automatic transmission. To fully utilize the potential of the new
3.5-liter engine and provide smoother, more refined shifting, the
transmission features revised programming of the Power
Control Module
(PCM) and clutch packs with additional plates to handle the
increased
power output. The solid-state PCM uses information on manifold
pressure, throttle position, drive-wheel speed and engine rpm to
determine upshift and downshift points. A "power mode" button
allows
the driver to extend the allowable engine rpm before an upshift,
letting the engine rev higher for better acceleration and downshift
sooner for enhanced engine braking. A "winter mode" button
holds the
transmission in third gear only when starting, for reduced
wheelspin
on ice or other slippery surfaces. A "torque management control"
feature in the PCM reduces torque output during shifts for
smoother
driving and enhanced durability of transmission components,
and
precludes the necessity of changing the transmission fluid for
the
life of the vehicle. To cope with severe duty conditions more
effectively, the transmission now features an electronic monitor
for
the automatic transmission fluid that can check fluid condition
instantly via the dealers diagnostic service system.
4-WHEEL DRIVE SYSTEM
The 1998 SLX is equipped with a sophisticated new 4-wheel
drive
system which offers the ultimate in convenience and flexibility.
Designed to be simple to operate, the new system allows
drivers to
switch between 2-wheel-drive and Torque-On-Demand (TOD)
four-wheel
drive modes by simply pushing a button. A total of three drive
modes
are provided: 2-wheel-drive, for normal on-road driving;
Torque-On-Demand 4-wheel-drive, for higher speed driving in
challenging driving conditions; and 4-wheel-drive low for serious
low-speed off-highway use.
2-WHEEL DRIVE MODE
When operating the SLX in 2-wheel drive mode, the transfer
case
directs 100% of the driving force to the rear wheels. Although the
new Torque-On-Demand system and powertrain enhancements
allow the SLX
to be operated in 4-wheel drive mode at any speed, the vehicle
retains the 2-wheel drive mode for quieter operation, increased
fuel
economy and reduced drivetrain wear during normal driving
conditions.
TORQUE ON DEMAND, 4-WHEEL DRIVE MODE
At the heart of the new Torque-On-Demand (TOD) 4-wheel drive
system
is a state-of-the-art transfer mechanism which is controlled
electronically by a sophisticated program incorporated in the
Electronic Control Unit (ECU). The TOD 4-wheel drive system
can be
engaged or disengaged on-the-fly at any speed below 60 mph
by simply
pushing the dash-mounted control button. Once engaged, the
SLX can be
operated in any speed range.
In the new transfer unit, power directed to the front wheels is fed through an electronically controlled multi-plate clutch that can instantly vary the amount of torque transmitted to the front wheels. Power to the front then passes through a chain and sprockets (for quieter operation), to the front drive shaft, through the front differential and to the front wheels via a new CV joint equipped varied driveshaft.
In TOD mode the amount of driving force applied to the front wheels is valued by the TOD computer program which controls the electro-magnetically actuated clutch in the transfer unit according to vehicle speed, engine load, throttle position and differences between front and rear wheel speeds.
During modest acceleration at small throttle openings, only a small amount of the total driving force is directed to the front wheels (between 0 and 15%). As the throttle is opened further, additional torque is directed to the front wheels until a full 50% of the total power output is directed to the front. However, if at any time the wheel speed sensors detect a difference in wheel speed between the front and rear wheels (i.e. wheel spin), the TOD system instantly changes the driving force to 50/50 front to rear distribution for optimum traction and control. The operation of this system is displayed on the TOD indicator in the instrument panel and the system is so smooth and seamless that it is virtually undetectable by the driver.
4 WHEEL DRIVE LOW
For the most demanding conditions, 4-wheel-drive low produces
the
ultimate in off-highly capabilities. Designed as a "locked"
part-time
system, the vehicle must be completely stopped to engage this
mode.
The floor mounted lever can be shifted directly into 4-wheel-drive
low from either 2-wheel-drive or TOD modes. Once engaged, the
front
and rear drivelines are locked, power is directed 50/50 to front
and
rear axles and a planetary gear set in the transfer unit is
engaged
to significantly reduce the overall gearing (2.48:1) of the vehicle
for low speed operation.
LIMITED SLIP DIFFERENTIAL
A longitudinal driveshaft transfers torque to both the front and the
rear differentials. The rear differential with a clutch-type limited
slip feature, automatically transferring power to the rear wheel
with
the most traction. Due to the increased power of the new engine,
the
final drive ratio has been raised from 4.55 to 4.30:1 thereby
making
the 1998 model quieter at cruising speeds. A larger diameter
ring and
pinion gear set is also used for increased durability.