1986 Acura Legend -- Drivetrain

The Legend's 2.5-liter V-6 engine is a light and compact high performance powerplant that owes much of its technology to Honda experience in Formula I racing. Its 90? "V" cylinder bore angle and SOHC configuration allow for both substantial power output and the relatively small outer dimensions which are necessary to achieve the low hood line dictated by the Legend's aerodynamic design.

Both the engine block and one-piece cylinder heads are precision die-cast from aluminum alloy, used for its light weight and heat dissipation qualities; the alloy pistons are molybdenum coated to minimize friction. The block has cast iron cylinder liners and is extremely rigid with the centerline of the crankshaft within the oil pan flange. The main bearing supports use six bolts, four vertical and two horizontal. These "cross bolted" mains are similar to those employed in racing engines.

The Legend's crankshaft, as with conventional V-6 crankshafts, has three throws and four main bearings. To overcome the problem of vibration caused by the uneven firing intervals associated with a 90° V-6, the crank pins are offset by 30°. This makes the firing interval an even 120°, resulting in smooth running, especially at idle. To further reduce vibration, the crankshaft is fitted with a dynamic damper.

The cylinder heads are complex, one-piece castings, with no separate cam case. The cams are located within the centerline of the intake valves and actuate self-adjusting, hydraulically damped finger-followers which open the valves. The exhaust valves are actuated with similar followers that transfer motion through a short link to rocker arms that open the valves.

The pent-roof combustion chamber, with a compression ratio of 9.01:1; uses four valves, at an included angle of 40°, to maximize valve area (intake valve diameter is 33 mm x 2, exhaust 27.5 mm x 2). The spark plug is in the center of each chamber for uniform and rapid flame-front propagation. This valvetrain design allows for the same efficient port shape land cross flow configuration that normally requires dual overhead cams.

The camshafts are coated with a special low friction alloy and lubricated by means of a forced-lubrication system incorporating oil galleries in the cylinder heads which provide constant lubrication to the cams, bearings arid finger-followers. A large volume, integrated oil filter/cooler is also part of the lubrication system.

Fuel delivery is by means of a multi-point-sequential, programmed fue1 injection system, which uses technology derived from Honda racing experience. The injection has three subsystems: Air Intake, Electronic Control, and Fue1 Delivery. The fuel/air ratio is kept at the optimum level by an eight bit microprocessor which analyzes information received from the following sensors:

A) Throttle Angle Sensor--A precision shaft angle transducer monitors exact throttle position. The computer uses this information to determine fuel injection quantity during all operating conditions.

B) Crank Angle Sensors (TDC and #1 cylinder) --The #1 cylinder sensor tells the computer when to start the sequential injection; and the top dead center (TDC) sensor monitors engine speed.

C) Coolant Temperature Sensor--A thermistor changes resistance as coolant temperature changes; the signal is used to tai1or injection duration to different engine conditions.

D) Intake Air Temperature Sensor--A thermistor measures intake air temperature and the computer adjusts injection duration to suit conditions.

E) Manifold Air Pressure (MAP) Sensor--A precision vacuum/pressure transducer monitors engine load; the computer uses the information to determine the proper basic injector discharge duration. Atmospheric Pressure Sensor--A transducer measures barometric pressure; its information is used by the computer to adjust injector discharge duration.

G) Oxygen Sensor--Monitors oxygen in exhaust gas; the computer uses the signal to adjust injection duration to maintain a stoichiometric air/fuel ratio for efficient NOx control by the three-way catalyst.

Utilizing information from the various sensors, the correct volume of fuel is injected into each manifold runner sequentially at a specific time just prior to the intake stroke. Fuel is automatically cut off during deceleration and interrupted at 6700 rpm to prevent over-revving.

Electronically controlled idle valves maintain a constant idle speed, and ignition is through a fully transistorized, solid-state system. A three-way catalyst is used for exhaust emission control.

Both a 4-speed automatic transmission and a 5-speed manual synchromesh are available.

To improve efficiency, the automatic transmission features a programmed lockup torque converter which can automatically lockup in 2nd, 3rd and 4th gear. This Programmed Lockup Converter system uses several sensors, including throttle opening and vehicle speed, to determine the correct lockup speed. Careful attention has been paid to the standard transmission. Shift-lever throws are short, and to insure crisp gear changes the shift-linkage mechanism is fitted with teflon bushings and a rubber bushed U-joint which isolates vibration. The clutch is operated hydraulically, and is adjusted automatically.

(5sp. Man.)
(4-sp. Auto)

Transmission Ratios:













Final Drive Ratio


The Legend's refined front-wheel drive system uses equal length driveshafts to reduce torque steer caused by unequal constant-velocity joint angles. The right side shaft is divided into inboard and outboard sections. The inboard section is supported by a bearing and connects to the outboard section by a constant-velocity joint. The length of this outboard section matches the length of the left side driveshaft. This results in equal constant velocity joint angles and the virtual elimination of torque steer.

The Legend uses power assisted rack-and-pinion steering (with a steering ratio of 17.6:2, 3.45 turns lock-to-lock, and a turning circle of 11 meters ([36.1 ft.]). The system is road-speed sensitive in that power assist progressively diminishes relative to speed. That is, maximum assist is available while parking and driving slowly, while at cruising speeds assist is reduced or eliminated as necessary to maintain road feel. For convenience, the steering column is adjustable.

To match its performance potential, the Legend is equipped with four-wheel disc brakes. The front discs are ventilated; power assist is provided by a 10-inch vacuum servo unit; and the braking system incorporates a front-to-rear proportioning valve. Dual diagonal hydraulic circuits are used to prevent total loss of braking power. In the event of hydraulic failure in one circuit, one front brake and the opposite rear brake remain operative.

The 262 mm (10.3-inch) diameter front discs are ventilated; the 260 mm (10.2-inch) diameter rear discs are solid and the rear brake caliper's incorporate a mechanical parking brake. Total front brake swept area is 1319.5 sq. cms (204.5 sq. in.) and total rear brake swept area is 1118.0 sq. cms.

To complement the Legend's power and handling capability, performance oriented Michelin MXV 205/60 R15 radial tires are used. They're mounted on light alloy, 5.5J x 15 wheels, specially coated to resist corrosion.

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