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Old 11 Sep 2007, 07:14 pm
Join Date: Aug 2007
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Default 2008 Acura RL - Powertrain

Torrance, Calif. - Sep 11 —


The RL powertrain features a 3.5-liter SOHC V-6 engine, VTEC® valvetrain
operation, a Sequential SportShift 5-speed automatic transmission with steering
wheel mounted paddle shifters and Grade Logic Control, and Super Handling All-Wheel
Drive™. The crankshaft of the RL is positioned transversely (side to side)
rather than longitudinally (front to rear), which allows the RL engine to be
packaged more tightly for better handling agility, without sacrificing interior

The advanced VTEC® engine develops 290 horsepower and 256 lb-ft of torque.
Fuel economy is EPA rated at 16/24 mpg* (city/highway) and it meets CARB LEV-2
ULEV requirements.

While not as powerful as some V-8 engines, the RL's high output V-6 is lightweight
for better acceleration and more nimble handling. To more effectively put power
to the ground, the RL comes standard with a Sequential SportShift 5-speed automatic
with steering wheel mounted paddle shifters that allow easy finger-tip-activated
manual operation.

To maximize available traction and to provide exceptional handling balance,
the RL comes standard with Super Handling All-Wheel Drive™ (SH-AWD™),
the first and only all-wheel drive system that distributes the optimum amount
of torque not only between the front and rear wheels but also between the left
and right rear wheels. The system's direct yaw control makes the cornering character
of the RL exceptionally neutral when under power.



  • 3.5-liter, SOHC, VTEC® V-6 engine produces 290 horsepower at 6200 rpm
    and 256 lb-ft of torque at 5,000 rpm

  • VTEC® (Variable Valve Timing and Lift Electronic Control)

  • 11.0:1 Compression ratio

  • Two-piece, dual-stage intake manifold

  • Direct ignition system with detonation/knock control

  • Variable flow exhaust system

  • Drive-by-wire throttle system

  • Computer-controlled Programmed Fuel Injection (PGM-FI)

  • Maintenance Minder System optimizes service intervals

  • 100,000 miles or more tune-up interval

Emissions/Fuel Economy

  • High-flow, close-coupled catalytic converters plus under floor catalytic

  • High capacity 32-bit RISC processor emissions control unit

  • Meets CARB LEV-2 ULEV standard

  • EPA estimated 16/24 mpg (city/highway)

Noise, Vibration & Harshness (NVH)

  • 60-degree engine cylinder V-angle for inherently smooth operation

  • Automatically tensioned, maintenance-free serpentine accessory drive

5-speed automatic with Sequential SportShift, paddle shifters and
Grade Logic Control

  • Quick-response Sequential SportShift allows semi-manual operation

  • Steering-wheel mounted manual-mode F1®-style paddle shifters

  • Coordination between drive-by-wire throttle system and transmission makes
    for quicker, smoother shifts

  • Wide gear ratio spacing for strong acceleration and good fuel economy

  • Advanced shift-hold control limits upshifts during spirited driving

  • Advanced Grade Logic Control System reduces gear "hunting" on steep hills

Super Handling All-Wheel Drive™ (SH-AWD™)

  • Fully automatic, full-time traction and handling enhancing system

  • Distributes torque between the front and rear wheels and between the left
    and right rear wheels to directly control the yaw moment of the vehicle

  • Understeer is reduced when cornering

  • Outer wheel capable of being overdriven by up to five percent during cornering


The 3.5-liter SOHC VTEC® V-6 in the RL is the most powerful sedan engine
in Acura's history and incorporates many of the refinements and improvements
that have been developed in other Acura powerplants. The RL engine has a smooth-firing
60-degree V-angle and compact overall dimensions. Aluminum alloy construction
saves weight and improves cooling, while free-breathing VTEC® cylinder heads
operate four valves per cylinder.

A high inertia intake system, increased compression ratio, close-coupled catalytic
converters and high flow exhaust help make the RL engine the most powerful normally
aspirated 6-cylinder engine in its class.


The lightweight, heat-treated die-cast aluminum-alloy cylinder block has cast-in-place
iron cylinder liners. These thin-wall, centrifugal-cast iron liners help reduce
the block's overall length and weight. With their rough outer surfaces, the
liners bond securely to the surrounding aluminum during the manufacturing process,
enhancing liner-to-block rigidity and heat transfer. The cylinder block also
incorporates a deep-skirt design for rigid crankshaft support and minimized
noise and vibration.


The RL V-6 uses a forged-steel crankshaft with revised counterweights to accommodate
the weight of higher compression pistons. With taller, reinforced crowns, these
new pistons provide a compression ratio of 11.0:1. Part of the reason the elevated
compression ratio is possible is due to an oil jet system that sprays cooling
oil on the underside of the piston crowns to help keep temperatures in check.
New steel connecting rods are forged in one piece and then the crankshaft ends
are broken, creating a lighter and stronger rod with a perfectly fitted bearing


Like the TL, the RL uses cast alloy single overhead camshaft (SOHC) cylinder
heads that incorporate tuned exhaust manifolds as an integral part of the casting.
Made of pressure-cast, low-porosity aluminum, these lightweight cylinder heads
improve overall packaging, enhance exhaust flow and allow the optimal positioning
of a primary close-coupled catalytic converter on each cylinder bank. To ensure
positive sealing, the RL has a three-layer type head gasket like that used on
the TL. A single Aramid-fiber reinforced belt drives the overhead camshafts.
The RL cylinder heads have 36mm diameter intake valves and 30mm diameter exhaust


Acura VTEC® (Variable Timing and Lift Electronic Control) is a major contributor
to the engine's large gains in horsepower and torque. The system operates the
12 intake valves in two distinct modes, so that the operation of the intake
valves continually changes to optimize both volumetric efficiency and combustion
of the fuel-air mixture. At low engine speeds, the intake valves have low lift
and are open a comparatively short period of time during cylinder filling. At
high engine speeds where breathing is critical, the valves switch to high-lift,
long duration mode to deliver improved volumetric efficiency. The VTEC®
changeover point occurs at 4950 rpm and is undetectable to the driver.

The RL uses a 3-rocker-arm VTEC® system similar to that of the MDX and
TL. This configuration allows each of a given cylinder's intake valves to be
controlled by its own low-speed cam lobe, allowing for staggered valve opening
and lift. (By comparison, with 2-rocker VTEC, a single low-speed cam lobe controls
both intake valves for each cylinder). Better air/fuel mixing in the cylinders
improves both combustion speed and combustion stability. When the engine reaches
4950 rpm, the powertrain control module (PCM) triggers the opening of an electric
spool valve that routes pressurized oil to small pistons within the intake valve
rocker arms. The rocker pistons slide into position to lock together the three
intake rocker arms in a given cylinder, which then follow a single high-lift,
long-duration cam lobe. The intake and exhaust valve timing and duration are
unique to the RL.


The RL uses a dual-stage intake manifold that is designed to deliver maximum
airflow to the cylinders. The 2-piece cast-aluminum manifold is also has the
advantage of being very light, reducing weight by 2.6 pounds over the previous

Working in concert with the VTEC® valvetrain, the induction system significantly
boosts torque across the engine's operating range. Internal passages and two
butterfly valves commanded by the powertrain control module (PCM) provide two
distinct modes of operation.

The valves are closed at lower rpm. In this mode, the three cylinders on each
bank draw air from only the nearer half of the manifold's internal plenum. The
volume of the plenum and the length of inlet passages are tuned to maximize
the resonance effect, wherein pressure waves are amplified within each half
of the intake manifold during certain rpm ranges. The amplified pressure waves
significantly increase cylinder filling and the torque produced by the engine
throughout the lower part of its rpm band. Funnel-shaped intake ports—similar
to those used on racing engines—are built in at the uppermost end of each
intake runner to improve airflow.

As the benefits of the resonance effect lessen with rising engine speed, the
butterfly valves open at 4000 rpm to interconnect the two halves of the plenum,
thus increasing its volume. An electric motor, commanded by the powertrain control
module, controls the connecting butterfly valves. With the valves open, each
cylinder draws intake air from the full plenum chamber. The inertia of the mass
of air rushing down each intake passage helps draw in more charge than each
cylinder would normally ingest. This phenomenon is the same effect produced
by a low-pressure supercharger. The inertia effect greatly enhances cylinder
filling and the torque produced by the engine at higher rpm.


The RL power afforded by the high 11.0:1 compression ratio is made possible
by a powertrain control module (PCM) that continually monitors engine functions
to determine the best spark timing. An engine block mounted acoustic detonation/knock
sensor "listens" to the engine, and based on this input, the PCM retards
the ignition timing incrementally to prevent potentially damaging detonation.
The RL has iridium alloy-tipped sparkplugs, each with an individual coil unit
positioned directly above it.


The Programmed Fuel Injection (PGM-FI) system monitors the exact state of
the exhaust gas and tracks multiple engine inputs including throttle position,
intake air temperature, coolant temperature, intake manifold pressure, and more.
Based on these inputs, PGM-FI continuously adjusts and optimizes the amount
of fuel delivered to each cylinder.


The RL utilizes a drive-by-wire throttle system that eliminates the need for
a conventional throttle cable. The system monitors various parameters like throttle
pedal position, throttle valve position, road speed, engine speed and gear position,
then adjusts the moment-to-moment relationship between pedal position and throttle
opening. By altering the amount of "gain" between the pedal and butterfly valve,
significant improvements in drivability and acceleration linearity are possible.

For smooth launches from a standing start the system has relatively little
gain, so that engine response is smooth and progressive. At higher speeds, the
gain increases to provide responsive acceleration for passing and hill climbing.
The Sequential SportShift 5-speed automatic transmission and Vehicle Stability
Assist™ (VSA®) with traction control are fully integrated with drive-by-wire.


The exhaust manifolds of the RL are cast directly into the alloy cylinder
heads to reduce weight and to position the engine's two primary catalytic converters
as close as possible to the combustion chambers. The 600-cell per-square-inch,
high-efficiency converters mount directly to the exhaust port of each cylinder
head for extremely rapid converter light off moments after the engine starts.
By eliminating traditional exhaust header pipes, this arrangement results in
a significant weight savings.

A hydroformed 2-into-1 collector pipe carries exhaust gases to a single 350
cell-per-inch secondary catalytic converter located under the passenger cabin.
To balance the engine's need for proper exhaust backpressure at low speed and
free flow at high speed, the exhaust system incorporates a variable flow rate
feature. An exhaust pressure-operated valve in the system has two operating
modes. The low speed mode has a flow rate of 130 liters per second; when the
engine reaches about 4000 rpm, the exhaust pressure raises enough to open the
valve, which increases the flow to 150 liters per second.


Although the RL's 3.5-liter V-6 has made power advances, it has also become
much cleaner. The V-6 now meets tough CARB LEV-2/ULEV emissions standards and
is certified to this level of emissions performance for 120,000 miles.

Many advanced technologies contribute to this emissions performance. The cylinder
head-mounted close-coupled catalysts light off quickly after engine start up,
and a 32-bit RISC microprocessor in the powertrain control module (PCM) boosts
computing power to improve the precision of spark and fuel delivery. Particularly
right after startup, better fuel atomization is provided by high-efficiency
multi-hole fuel injectors that better direct fuel around the intake valve stems.

Current CARB* Emission Standards (gram/mi.)






LEV-I LEV @ 100k




'04 3.5 RL

LEV-I ULEV @ 100k





LEV-2 LEV @ 120k





LEV-2 ULEV @ 120k




'05-'08 RL

LEV-2 SULEV @ 150k










*California Air Resources Board


With its 60-degree V-angle and compact, rigid and lightweight die-cast aluminum-alloy
block assembly, the new RL powerplant is exceptionally smooth. Other factors
that reduce noise and vibration are a rigid forged crankshaft, die-cast accessory
mounts, and a stiff, cast aluminum-alloy oil pan.


The RL requires no scheduled maintenance for 100,000 miles or more, other
than periodic inspections and normal fluid and filter replacements. This first
tune-up includes water pump inspection, valve adjustment, replacement of the
cam-timing belt and new sparkplugs.


To eliminate unnecessary service stops while ensuring that the vehicle is
properly maintained, the RL has a Maintenance Minder system that automatically
monitors the vehicle's operating condition. When maintenance is required, the
driver is alerted via a message on the Multi-Information Display (MID).

The system monitors operating conditions such as oil and coolant temperature
along with engine speed to determine the proper service intervals. Depending
on the operating conditions, oil change intervals can be extended to a maximum
of 10,000 miles, potentially sparing the owner considerable money and inconvenience
over the life of the car. The owner-resettable system monitors all normal service
parts and systems, including

oil and filter, tire rotation, air-cleaner, automatic transmission fluid, spark
plugs, timing belt, coolant, brake pads and more. To prevent driver distraction,
maintenance alerts are presented when the ignition is first turned on, not while


To maximize acceleration performance, fuel economy and driver control, the
RL has a standard 5-speed automatic with Sequential SportShift, paddle shifters
and Grade Logic Control. Mechanically related to the extremely compact transmission
that made its debut in the previous generation MDX, the RL unit has upgrades
and enhancements to suit the greater power output and higher engine speeds of
the RL.

Designed for low maintenance and a high level of durability, the RL transmission
requires no scheduled service until 120,000 miles when operated under normal
conditions. To provide strong off-the-line acceleration coupled with a relaxed,
fuel-efficient cruising rpm, the unit has the widest ratio spread of any 5-speed
automatic transmission in the RL's class.

Automatic Mode

The Sequential SportShift transmission can be operated in a conventional fully-automatic
mode via a front center console-mounted gated shifter. When in automatic mode,
the transmission incorporates an advanced Grade Logic Control System and Shift
Hold Control, both of which work to reduce gear "hunting" and unnecessary

Shift Hold Control keeps the transmission in its current (lower) gear ratio
when the throttle is quickly released and the brakes are applied (as might be
the case when decelerating to enter a corner). Shift Hold Control leaves the
chassis undisturbed by excess shifting, ensuring that abundant power is immediately
available without a downshift.

Grade Logic Control alters the 5-speed automatic's shift schedule when traveling
uphill or downhill, reducing shift frequency, and improving speed control. Throttle
position, vehicle speed and acceleration/deceleration are continuously measured,
then compared with a map stored in the transmission computer. The Grade Logic
Control System then determines when the car is on a hill; if this is the case,
the shift schedule is adjusted to automatically hold the transmission in a lower
gear for better climbing power or increased downhill engine braking.

Manual Mode

The Sequential SportShift transmission can be shifted into manual mode by
moving the front center console-mounted selector lever laterally to a special
gate to the left of the "Drive" position. The RL offers two ways to
change gears when in manual mode: either by a push or pull of the shift lever,
or via F1®style paddle shifters mounted on the steering wheel. A digital
display in the tachometer face indicates which gear the transmission is in.
To heighten control and driver involvement, special shift logic in manual mode
delivers quicker, firmer shifts than when in fully automatic mode.

To help protect the engine and drivetrain from damage, an array of preventative
features are active when the transmission is in manual mode. In second, third
and fourth gears, the logic changes and the transmission ECU cuts off fuel flow
to the engine if there is a possibility of over revving.

In the rare situation where the fuel cutoff alone is unable to prevent engine
over revving (as could happen on a steep downhill), the transmission will automatically
upshift to prevent engine damage. And finally, when downshifting, the transmission
won't execute a driver-commanded downshift that would send the engine beyond
redline in the lower gear. The Sequential SportShift transmission will automatically
downshift to first gear as the vehicle comes to a stop as to prevent lugging
away from a stop in second gear.


The RL benefits from an innovative 5-position shift gate that simplifies the
operation of the transmission. The gate features a quiet linkage and a speed-controlled
reverse lockout solenoid to prevent transmission damage. When operated in automatic
mode, the transmission lets the driver choose D (1st through 5th gear) or D3
(1st through 3rd gear). Engine braking can be provided by moving from D to the
D3 position, downshifting from 5th, 4th or 3rd gear, depending on the vehicle


Both shift speed and smoothness are improved by cooperation between the drive-by-wire
throttle system and the electronically controlled automatic transmission. The
engine can be throttled by the engine management system during upshifts and
downshifts, the function of the engine and transmission can be closely choreographed
for faster, smoother shifting. As a result, the peak g-forces (or "shift
shock") are reduced significantly during upshifts and downshifts.


Super Handling All-Wheel Drive™ (SH-AWD™) is an innovative all-wheel
drive platform that distributes the optimum amount of torque not only between
the front and rear wheels but also between the left and right rear wheels. SH-AWD™
goes a step beyond conventional all-wheel drive by actively controlling the
torque delivered to each rear wheel during corning. The result is more neutral,
accurate steering when cornering under power that front-drive, rear-drive or
conventional all-wheel-drive can't equal.

Torque splits are as follows:

  • During straight-line cruising and moderate cornering below half throttle,
    up to 70-percent of engine torque is delivered to the front wheels.

  • In full-throttle straight line acceleration, up to 40-percent of the power
    is sent to the rear axle.

  • In hard cornering, up to 70-percent of available torque goes to the rear
    wheels for enhanced chassis balance. Up to 100-percent of this torque can
    be applied to the outside rear wheel that can also be overdriven up to five
    percent by a built-in acceleration device if the situation dictates.

SH-AWD™ ingeniously varies the amount of torque to the left and right
rear wheels. When cornering, a planetary gear set overdrives (or accelerates)
the rear wheels while individual right and left clutch packs direct torque to
either or both rear wheel(s), faster than the average of the front wheels to
dramatically enhance the cornering, steering feel, overall handling and stability
of the RL. The result is class leading cornering precision as well as enhanced

Direct Yaw Control System Theory

SH-AWD™ counters understeer with a Direct Yaw Control System when under
power. Spinning the outside rear wheel faster than the average speed of the
two front wheels allows the system to use engine power to yaw the vehicle while
turning. By relieving the front tires of some of the work of turning the car,
the system reduces understeer and the vehicle stays more balanced and controllable.
In addition, with the cornering load more evenly distributed between the front
and rear tires, the total cornering grip is increased. In conventional cars,
cornering is created almost entirely by the steering angle of the front tires.
With the RL, cornering is created by steering angle of front tires combined
with the extra drive torque supplied by an outside rear tire.

This is a significant advance over conventional drive systems. To deal with
high power output, front- or rear-drive systems generally use some type of limited-slip
device to maintain traction under power. The linking effect of the inside and
outside drive wheels in these systems resists turning, however. This is a factor
that works against the front tires as they attempt to turn the car. Conventional
AWD systems have a similar linking effect between the inboard and outboard tires
and front and rear axles, causing a similar resistance to turning. This is part
of the reason why traditional AWD systems typically lack the more nimble feel
of the best two-wheel drive systems. By using drive torque to help turn the
car, the RL is more responsive, neutral and predictable, while simultaneously
offering all of the usual benefits of all-wheel drive.

Electronic Controls and Parameters

The logic and control of SH-AWD™ is integrated with the RL Engine Electronic
Control Unit (ECU) and Vehicle Stability Assist™ (VSA®) ECU. The Engine
ECU provides engine rpm, intake manifold pressure, and transmission gear ratio
data. The VSA® ECU provides data on lateral g, yaw rate, wheel rotation
speed and steering angle. The SH-AWD™ ECU monitors the status of the acceleration
device and the right and left Direct Electromagnetic Clutch torque. Traction
is calculated based on the information from the engine ECU. During an acceleration
situation, lateral g and steering angle are used to calculate the torque split
between the right and left rear wheels. At the same time, this data is used
to control the acceleration device.

SH-AWD™ System Layout

SH-AWD™ is a full-time all-wheel drive system that requires no driver
interaction for operation. A torque transfer unit is bolted directly to the
front-mounted transaxle. Attached to the front differential ring gear is a helical
gear that provides input torque to the transfer unit. A short horizontal shaft
and a hypoid gear set within the case turn the propeller shaft ninety degrees
and move it to the vehicle center line. A lightweight carbon fiber reinforced
composite propeller shaft carries power to the rear drive unit.

The rear drive unit of the RL contains three planetary gear and clutch sets.
Torque from the propeller shaft passes through the first clutch/planetary gearset,
which as a unit is called the Acceleration device.

Output torque from the Acceleration device is carried a short distance rearward
to a hypoid gear that turns the output 90-degrees and drives the rear axle shafts.
A matched pair of Direct Electromagnetic Clutch systems, one on each side, send
power to each rear wheel. These clutch systems can be controlled as a pair to
alter the front/rear torque split, or depending on the situation, the rear wheels
can receive between 30- to 70-percent of the engine's total output. The right
and left Direct Electromagnetic Clutch systems can also be controlled independently,
to allow up to 100-percent of the total rear axle torque to go to only one rear

Acceleration Device

Positioned at the front of the RL rear drive unit, the Acceleration device
typically passes torque to the rear axle at very close to a one-to-one ratio.
In cornering, however, the Acceleration device's output shaft spins faster than
its input shaft.

The Acceleration assembly uses a compact planetary gearset to achieve its
speed increase. Hydraulic actuators operate clutch packs that control the planetary
gearset. When the input shaft is locked with the planetary gear carrier, there
is no ratio change (this is the straight-line mode). During cornering, the carrier
is coupled with the case, and the output shaft speed increases up to five percent.
A speed sensor at the hypoid gear, downstream of the Acceleration device, provides
a feedback loop to the SH-AWD™ Electronic Control Unit to ensure that
the system is working properly.

Direct Electromagnetic Clutch Systems

Located on either side of the hypoid gear that drives the rear axle, two identical
Direct Electromagnetic Clutch systems control the amount of drive torque that
reaches each rear wheel, and provide limited-slip differential function. An
electric coil controls the pressure applied to a clutch, which slows the sun
gear in a planetary gearset to modulate the torque that is sent to the wheel.
The amount of torque transmitted to each rear wheel can vary continuously, between
zero and 100-percent, depending on the conditions.

Under deceleration (throttle closed) while cornering, torque to the outside
rear wheel is varied to change from an inward to an outward yaw moment, helping
vehicle stability. A search coil sensor allows the ECU to estimate the clutch
plate coefficient of friction (that changes with heat) and then adjusts voltage
sent to the electromagnetic coil that controls the clutch to compensate. To
ensure that the amount of torque transmitted remains optimized as miles and
wear accumulate, a coil provides a feedback loop that the ECU uses to adjust
voltage to the electromagnetic clutches to compensate for clutch wear.

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