1990 Acura Integra - Drivetrain

Design Objectives

Power and performance are inseparable. and the goal of the engineers who designed the 1990 Integra's engine was to provide more of both. The new engine they developed produces 130 horsepower. a 10 percent increase. It is a 4-cylinder. dual overhead cam.16-valve engine with a displacement of 1.8 liters.

The new engine is specifically designed and tuned to provide power over a wider rpm range. improving all-around driving performance in general. and low- and mid-range performance in particular. To this end. torque has been increased 17.5 percent. to 121Ibs.-ft.. with the biggest improvement coming in the 2000 to 5500 rpm range. There is approximately 15 percent more torque at 2000and. as revs increase. it builds to a 17.5percent increase at 5000 rpm. where maximum torque occurs.

New transmissions -- a standard 5-speed manual and available electronically-controlled 4-speed automatic with driver-selectable sport mode -- were developed to accommodate the Integra's additional power and improve driveability. The manual transmission uses a larger clutch and synchronizers to improve shift quality. The automatic transmission has three parallel shafts instead of two. making it shorter and more compact.

As before, the new Integra uses equal-length half shafts to virtually eliminate torque steer.

Engine

- Cylinder Head and Induction System -

The Integra's cylinder head is a compact, aluminum die casting with pent roof (modified hemisphere) combustion chambers and centrally located spark plugs. With multiple valves and carefully tuned intake and exhaust ports, the cylinder head is able to "breathe" very efficiently.

This combustion chamber shape is widely accepted as the best configuration for an internal combustion engine. Its layout is nearly identical to the design of Honda's championship-winning Formula 1 engines.

To further improve volumetric efficiency and boost low-end power, a new high-velocity intake manifold was developed with narrower and shorter runners that are 38.5 mm (1.52 in.) in diameter and 296 mm (11.6 in.) in length. Valve timing was changed to accommodate the higher velocity and valve size was increased -- both the 31 mm (1.220 in.) intake and 28 mm (1.102 in.) exhaust valves are 1 mm (0.039 in.) larger than before.

Valve actuation is by means of finger-follower type swing arms. These permit a more compact design since the camshafts can be located closer to the center line of the cylinder head. Also, the finger followers, compared to rocker arms, are lighter to reduce reciprocating weight.

- Cylinder Block -

Like the first generation Integra engine, the new engine's cylinder block is die-cast aluminum. But since its bore centers are 90 mm (3.54 in.) apart, 6 mm (0.236 in.) further than before, it is substantially different. The additional spacing made the block somewhat longer, but it allowed for ,an increased bore and permitted the use of a more rigid crankshaft.

The engine block is cast with an integral main oil gallery, a refinement that cut 1.5 kg (3.3Ibs.) from its weight. Even though it is lighter, the new block is more rigid due to its heavier main bearing webs and a 30-35 mm longer skirt. The changes in the block design also helped reduce noise and vibration by raising the basic powerplant resonant frequency by 750 rpm. Engine height is virtually unchanged, an important consideration which makes it possible for the Integra to retain its distinctive sharply sloping hoodline.

The new engine's larger displacement, 1.8 liters as against the previous 1.6, is a result of increasing the bore to 81 mm (3.19 in.) from 75 mm (2.95 in.). The stroke is actually slightly less, going from 90 mm (3.54 in.) to 89 mm (3.50 in.). The larger, displacement and improved induction helped raise horsepower by 10 percent, to 130 at 6000 rpm. Torque has risen by 18 foot-pounds, 17.5 percent more, to 121 at 5000 rpm.

Additional changes were made to improve both drive ability and reliability by reducing vibration, including the development of a new crankshaft torsional damper and driven pulley, and the use of improved drive belts for accessory systems.

Programmed Fuel Injection

Precise control of fuel induction is essential for instant throttle response, smooth acceleration and engine efficiency. To provide such control, the Integra engine's programmed fuel injection uses an eight-bit microprocessor. It directs the system so that the correct amount of fuel is injected into each intake port at the proper moment.

Fuel injection timing is determined by monitoring seven engine factors: throttle angle, crankshaft angle, coolant temperature, intake ah temperature, manifold air pressure, atmospheric pressure, and exhaust gas oxygen content. The computer analyzes this information and continually adjusts the injection system to maintain the optimum fuel/air ratio. A fully transistorized ignition controls the timing, duration and intensity of the spark.

Several modifications have been made to the induction system to improve drive ability. An eccentric drum is used in the throttle body so that the transition from idle to full throttle is smoother and more progressive. Pedal feel has been improved by replacing brass bushings with ball bearings.

The transmission itself has been redesigned to accommodate larger diameter synchromesh gears -- from 61 mm (0.240in.) to 66 mm (0.260 in.) -- to improve durability and assure positive gear changes. The mounting flange of the transmission has also been redesigned to incorporate a double-wall flange that helps reduce noise and vibration while increasing driveline rigidity.

The manual transmission's gear ratios have been revised to match the power and torque curves of the new engine. Due to increased engine output, it was possible to use slightly higher ratios for third, fourth and fifth gears. The new Integra offers improved acceleration while maintaining fuel economy at cruising speeds.

Automatic Transmission

The Integra's automatic transmission is a new design that uses three parallel shafts instead of two to make it more compact. It incorporates a number of changes that improve shift quality and reliability, including a larger diameter clutch with 24 percent greater load capacity. Like the standard transmission, the automatic has a double-wall flange around its outer perimeter for better load dispersion and reduced vibration.

There's also a new cruise control system which uses an electric motor to operate the throttle so that the speed selected by the driver is maintained. With electric control, response time is quicker and a constant speed is more easily held because the system is not influenced by changes in vacuum pressure. When driving on long grades or mountainous roads this electric system can hold a chosen speed with more consistency than a vacuum system. It has the further advantage of being 55 percent smaller in size for more efficient use of under-hood space.

Manual Transmission

To match the higher output of the Integra's new engine, significant driveline changes were made to insure that durability and reliability are equal to performance.

For manual transmission-equipped Integras, there's a larger clutch. Its diameter is increased from 200 mm (7.87 in.) to 220 mm (8.66 in.) to reduce its operational load and improve both pedal feel and wear resistance. The clutch case is perforated to aid cooling and the clutch disc is lined with non-asbestos material. As in the first generation Integra, the transmission is rod-actuated and each shift throw is short, crisp and precise.

For improved performance and efficiency, the new transmission has a lockup torque converter that's operational in second, third and fourth gear when accelerating, and third and fourth when decelerating.

There's also a driver-selectable Sport mode which permits the driver to choose a shift pattern more appropriate to spirited driving. When the driver selects the "S3" mode, the transmission shifts at higher rpm points, at partial throttle openings, from first to second, and second to third gears. To shift to fourth gear in the Sport mode, the driver presses the "84" button. Using the Sport mode increases responsiveness and is useful on long grades or mountain roads to keep the transmission from "hunting" for gear ratios.

All automatic transmission Integra automobiles are equipped with a shift lock system requiring that the brake pedal be depressed by the driver before the car can be shifted from "Park".

Front Wheel Drive

One of the innovative technical features that made the first generation Integras among the best handling cars in their class was their equal-length half shaft front-wheel drive system. The new Integras use an evolutionary progression of that system, and Integras with manual transmissions use new, refined tri-pod driveshaft joints that reduce vibration.

The most beneficial effect of this system is to virtually eliminate torque steer, a characteristic of some front-wheel drive cars to pull in one direction or another under hard acceleration. This tendency is minimized by equal-length half shafts because the angles of the constant velocity joints of each axle are the same. This symmetry keeps the car tracking true even under acceleration.

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