1993 Acura Legend Coupe Powertrain
1993 Acura Legend Coupe Powertrain
The 1993 Legend Coupe Type II engine has the same 3206cc displacement and
9.6:1compression ratio as the Type I engine. This engine, however, produces
230 hp at 6200 rpm and 206 1bs-ft of torque at 5000 rpm. To achieve this higher
power rating, a number of refinements were made to increase intake and
exhaust efficiency. In typical Acura fashion, power increase was achieved
through refinements of the existing operating systemsrather than by add-on
power-enhancing devices or the all-too-common approach of increasing
displacement - which tends to increase weight. This ability to attain
horsepower increases without sacrificing efficiency is a hallmark of the
engineering philosophy behind every Acura automobile.
Valve Timing, Lift and Size
Valve timing was altered to enhance high-end power over 5000 rpm while still
maintaining ample low-end torque. The intake valves open sooner and close
later when compared to the engine of the 1992 Coupe. The exhaust valves open
sooner but close at the same time as the 1992 Coupe engine.
|Type I||Type II|
|Valve Timing Change||200 HP||230 HP|
|Intake valves open||15ATDC||10ATDC|
|Intake valves close||30ABDC||40ABDC|
|Exhaust valves open||30BBDC||35BBDC|
|Exhaust valves close||10BIDC||10BTDC|
In addition, overall valve lift was also increased:
|Valve Lift Change||Type I||Type II|
|Intake valves||9.6 mm||10.2 mm|
|Exhaust valves||9.2 mm||9.5 mm|
The intake valve area was also increased to promote better breathing:
|Valve Diameter||Type I||Type II|
|Intake valves||33 mm||34 mm|
|Exhaust valves||28 mm||28 mm|
Six-Speed Manual Transmission
To fully utilize the benefits of the increased engine power, and to improve
efficiency at cruising speed, the Legend Coupe features a newly developed
6-speed manual transmission. Third, fourth and fifth gears are lower in order to
enhance acceleration. This gives the Coupe a decidedly more sporty personality.
At the same time, fuel efficiency at cruising speeds is also enhanced due
to the tall, overdrive sixth-gear ratio. To avoid accidentally shifting into reverse
while shifting into sixth, the transmission features an electric lockout system.
To reduce noise, vibration and tip-in shock, the 6-speed manual transmission
has been equipped with a dual-mass flywheel. Rather than having a
conventional flywheel, this unit is divided into two flywheels with torsion
springs and a viscous damper sandwichedbetween the two. In addition to
providing significantly smoother clutch engagement, this design reduces
flywheel inertia, which contributes to enhanced transmission durability and a
reduction of shift load and shock. This also reduces the level of transmission
noise at idle as well as under power.
Four-Speed Automatic Transmission
The optional, electronically controlled, 4-speed automatic transmission has
significantly refined for 1993. To minimize shift-shock during upshifts and downshifts, refinements were made in the oil pressure control unit. By exercising more precise control over oil pressure changes during automatic shifting, gear engagement is now smoother and less abrupt. In addition, the ignition timing is also momentarily retarded during upshifts to reduce engine power and achieve smoother shifting.To reduce shift-shock when changing from neutral to drive, a variable orifice valve has been developed. Similarly, to reduce shift-shock when shifting from neutral to reverse, the accumulator volume has been increased. To add a further measure of refinement, the gear tooth contact has been improved in order to reduce gear noise.
Traction Control System (TCS)
The LS Coupe features a Traction Control System (TCS) similar to that found in the NSX. It is designed primarily to enhance performance and stability. Although the basic technology is the same as that of the NSX, some alterations were necessary to adapt it to the different power and packaging demands of the Legend Coupe. This unit features an exclusiveDC motor and control unit, a second throttle valve, alateral acceleration sensor and a new indicator system. Using the wheel-speed sensors of the Anti-Lock Braking System (ABS), the TCS control unit measures the rotational speed of the front and rear wheels.
Using the rear wheels to estimate road speed, traction control is activated
the rotational speed of the front wheels exceeds that of the rears by a specified
amount. Based on the road speed and the speed difference between the right and left rear wheels, the ECU calculates the vehicle's actual yaw rate. This is compared with a reference yaw rate model in the ECU, based on steering wheel angle, to obtain a yaw rate difference. If this difference between actual and reference yaw rate exceeds a predetermined limit, the control unit signals the throttle actuator to partially close the throttle valve and reduce engine power. This helps the Coupe maintain good directional response and path following. The lateral acceleration sensor is used in combination with a longitudinal acceleration estimate from the wheel-speed sensors to estimate total vehicle acceleration. Based on a friction ellipse concept, this is used to further modulate throttle opening to improve traction performance.
A similar sequence of events occurs on a split friction surface where one front
wheel has more traction than the other. If the difference in speed is significant, engine power is reduced. A unique feature of this system also comes into play on rough road surfaces by sensing the variation in wheel speeds, as they accelerate and decelerate over bumps and holes, and allowing a controlled amount of wheel spin to improve acceleration.
1993 Acura Legend Coupe Chassis
Specific objectives for the Legend chassis performance called for active, driver oriented handling characteristics, very low noise and vibration, and excellent braking feel. The 1993 Coupe was refined to accommodate enhanced performance characteristics, which include new damping settings, new compliance bushings and better handling and ride.
A fundamental factor contributing to the precise handling of the Legend is
excellent 60/40front/rear weight distribution. Chassis engineers consider this the ideal distribution for a front-drive automobile with sporting aspirations.
The Legend powertrain incorporates a unique aluminum front subframe. This
is not only lighter,but more rigid compared to a steel subframe. It is mounted to themain structure at eight optimum points with specifically tuned bushings designed to isolate vibration and distribute loads throughout the structure. While these bushings are soft enough to block out vibration, they are still hard enough to prevent torquing and shifting which could, in an inferior design, disrupt suspension alignment and upset the carefully calibrated geometry.To improve ride quality, the front bushing of the lower control arm has been recalibrated from 20kg/mm to 45 kg/mm for 1993.
The double-wishbone front and rear suspension features widely spaced upper
and lower wishbones that give precise suspension action. The coil-over spring/damper units are designed to be free of the binding caused by the side-loading inherent in less sophisticated strut-type designs.
The rear suspension features upper and lower lateral arms carried on a steel
subframe. Two tubular trailing arm elements, bolted together into a unit, perform the function of fore/aft location and countering of braking torque. This system reduces unsprung weight by almost 20 lbs over the first-generation Legend, and it is also more rigid overall. The Coupe suspension has been specially tuned to provide more precise handling and response and to maximize traction. The rear bushing of the lower control arm has been recalibrated from 1000kg/mm to 750kg/mm to enhance steering effect under lateral force in cornering. The trailing arm bushing has alsobeen recalibrated from 45 kg/mm to 50 kg/mmto further minimize suspension movement and enhance rear suspension precision.
Shock Absorbers And Stabilizer Bars
Sophisticated gas-pressurized shock absorbers also contribute to the ride comfort and handling of the Legend. They feature an exclusivevalve mechanismcalled the HondaProgressive Valve (HPV). In this design, the valve opens and closes progressively, rather than being simply open or closed. This improves the shock absorbers' response to quick wheel movements and results in better rebound control as well. In both cases, tire-to-road adhesion is enhanced. The front and rear shock absorber damping rates have been revised and fine-tuned for enhanced ride quality as well as improved handling precision. Suspension bushing hardness was also increased front and rear and changed to a linear rate, rather than a progressive rate, in order to minimize suspension deflection, thus improving precision.
Stabilizer bar diameters have been matched to the suspension geometry,
springing and shock absorbers. The tubular front bar is 1.13inches (28.6mm) in
diameter with a wall thickness of 0.14inch (3.5 mm). The rear bar is tubular, with a 0.75inch (19.1mm) diameter, and a 0.12inch (3.0 mm) wall thickness.
The Legend features rack-and-pinion steering with a speed-sensitive, variable power assisted system. For optimum steering feel, the variation in power assist is more linear. The system's vane-type assist pump has high capacity for immediate response to quick steering wheel motions, while operating quietly.
For 1993, the Legend Coupe features power-assisted, four-wheel disc brakes with new dual-piston front brake calipers. The dual-piston front calipers are exclusive to the Coupe and offer enhanced braking force. The front rotor thickness has been increased from 23mm to 28mm for 1993. The ventilated front and solid rear discs are 11.0inches (280 mm) in diameter. A drum-in-disc parking brake is used in order toenhance parking brake power.
Anti-Lock Braking System (ABS)
Standard in both models is a Honda R&D-designed Anti-Lock Braking System
(ABS), which has four wheel-speed sensors and three channels. This system
modulates each front wheel individually and modulates the rear wheels as a single
unit. In order to ensure maximum reliability, this system uses a separate accumulator and brake fluid reservoir system. Even in the event of a complete loss of ABS brake fluid, the hydraulic braking system will still continue to operate and provide effective braking force.
In operation, the four wheel-speed sensors monitor changes in wheel speed. If
the sensors detect impending lockup under hard braking, they signal the control unit which then very rapidly modulates brake line pressure. By creating this pumping motion in the brake line pressure, it allows the wheels to continue rotating and thus allows the driver to retain steering control under maximum braking effort.
Wheels And Tires
The L model Coupe features 6.511x 15-inch alloy wheels with Michelin MXV4 All Season 205/60R15 91V tires. The LS Coupe model features 6.511x 16-inch alloy wheels with Michelin XGT-V4 All Season 215/55R16 91V tires. The LS tire and wheel package has been specially developed to maximize performance, handling, road feel, steering precision and stability.