1993 Acura Integra- Powertrain

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OVERVIEW

The goal of the engineers who designed the engine for the 1993 Integra was to provide more power and increased torque, while retaining the strengths and basic design of the 1.8-liter, second-generation Integra powerplant. The engine received a 10-hp increase in the 1992 model year, raising it to 140hp. It is an all-aluminum, transverse-mounted, 4-cylinder, dual overhead earn, 16-valve design.

A standard 5-speed manual transmission, and an optional electronically controlled 4-speed automatic, with driver-selectable Sport Mode are available. The GS-R 5-speed manual transmission features shorter (numerically taller) gear ratios to fully exploit the added horsepower. No automatic is available in the GS-R. The Integra uses equal-length halfshafts to virtually eliminate torque steer.

CYLINDER HEAD AND INDUCTION SYSTEM

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

This combustion chamber shape is widely accepted as the best configuration for a 4-valve-per-cylinder internal combustion engine. Its layout is nearly identical to the design of Honda's championship-winning Formula One engines.To further improve volumetric efficiency and boost low-end power, a new high-efficiency intake manifold was developed.

PROGRAMMED FUEL INJECTION (PGM-FI)

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

MANUAL TRANSMISSION

The manual transmission's gear ratios were revised in the 1992 model year to match the power and torque curves of the engine. Due to increased engine output, it was possible to use slightly taller ratios for first, second, third and fourth gears; the final drive ratio has been shortened slightly. The gear ratios of the GS-R 5-speed manual transmission are numerically higher than those of the rest of the Integra line to fully optimize the performance of the 160-hp engine.

AUTOMATIC TRANSMISSION

The automatic transmission has a programmed lockup torque converter that's operational in second, third and fourth gear when accelerating, and third and fourth gear 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 "S4" 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.

GS-R POWERTRAIN OVERVIEW

The GS-R engine is a development of the 1.6-liter VTEC engine used in the Japanese-market Integra. Using this engine as a starting point, the engineers increased displacement to 1.7 liters by lengthening the stroke from 77.4mm to 81.4mm. The stroke of the GS-R engine is 7.6mm shorter than that of the standard 1.8-liter Integra engine; this was necessary to achieve the high revving capability required for the VTEC engine.

The GS-R engine is a 1678cc, all-aluminum, transverse-mounted, 4-cylinder design with pent-roof combustion chambers and 4 valves per cylinder.Valve actuation is by dual overhead camshafts, driven by a toothed, rubber-composite belt. The GS-R engine produces 160 horse power at 7600 rpm, and 16.1 kilogram/meters (117Ibs-ft) of torque at 7000rpm. Engine redline is 8000 rpm; fuel cutoff is set for 8100 rpm. The 8000-rpm redline makes the GS-R engine the highest-revving 4-cylinder production powerplant sold in the U.S. Its redline equals that of the manual transmission equipped NSX.

ENGINE BLOCK, CRANKSHAFT AND CYLINDER HEAD

The cast-aluminum engine block is a deep-skirt design, with the walls of the block extending downward a significant distance below the centerline of the crankshaft. This stiffens the block, helping to reduce vibration and maintain bearing alignment at very high rpm levels. Steel cylinder liners are cast into the aluminum of the block.

The crankshaft of the GS-R is a steel forging, and the journals are polished to much closer tolerances than is customary in production engines. This expensive micro-finish polishing process is used in the NSX and in hand-built race engines, such as the Honda Formula One engines. The roughness of the bearing journals is decreased from 0.8 microns to 0.4 microns, compared to the conventional lapping process, and the allowable variation in the roundness of the journals is reduced from 7 microns to 4 microns. The extremely precise finishing of the crankshaft improves durability at extremely high engine speeds, and reduces overall friction significantly.

The cylinder head is a low-pressure aluminum casting.The combustion chambers are of a pent-roof design, with a generous squish area outboard of the valve seats to enhance mixture turbulence and increase combustion efficiency. The compression ratio is 9.7:1.The spark plugs are centrally located for optimum flame propagation. Because of the high rpm potential of the engine, special measures were taken to ensure adequate cooling. The pistons are cooled byjets of pressurized oil directed at the underside of the piston crowns, a technique also used in the Honda Formula One V-6 turbo and V-10 normally aspirated engines.The resulting lower piston temperatures allowed the pistons to be made lighter, reducing reciprocating weight and improving throttle response.

VARIABLE VALVETIMING AND LIFf ELECfRONIC CONTROL (VTEC)

Without question, the Variable ValveTiming and Lift Electronic Control (VTEC) system is a breakthrough in engine technology that eliminates the traditional tradeoffs between low-end torque and high-end power. The VTEC system used in the GS-R is essentially identical to that used in the NSX.

The heart of the VTEC system is a unique camshaft and rocker arm system. For each cylinder's set of two intake (and exhaust) valves there are three corresponding lobes on the camshaft. The two outboard lobes each have a profile suited for ]ow-to mid-rpm operation. The third, or center, cam lobe has a dramatically different profile designed for longer duration and higher lift-this lobe profile is designed to optimize breathing and horsepower production at high engine speeds. At part throttle, and in low-load situations, this third lobe is inactive.

During high-speed operation, the VTEC computer sends a signal to a spool valve, whichin turn delivers engine oil to small pistons in the rocker arms. Oil pressure causes the pistons to slide between the rocker arms, locking all three rocker arms together. Once locked together, the rocker arms are forced to follow the center cam lobe, with its higher lift and increased duration. The crossover from low lift to high lift occurs in 0.1 second and is virtually undetectable to the driver.

To promote swirl in the combustion chamber and improve combustion efficiency, the two individual intake (and exhaust) valves for each cylinder operate with different timing and lift specifications during low-speed operation. Once the VTEC system engages, the intake (and exhaust) valve pairs for each cylinder operate together. VTEC uses a dedicated CPU which monitors a number of engine operating parameters and activates the system only when certain conditions are met. It's designed to engage at approximately 5500 rpm, and will not engage under a "no load" situation, such as when the transmission is in neutral or when the clutch is disengaged.

To further improve intake efficiency,the GS.R intake valves are 33mm in diameter, 2 mm larger than those of the 1.8-liter Integra engine. The exhaust valves are 28 mm in diameter, the same diameter as those of the 1.8-liter engine.

INDUCTION SYSTEM

The GS-R engine uses a "high response" intake manifold for improved engine breathing at high engine speeds. The diameter and length of the aluminum manifold runners are tuned for maximum inertia effect, and to optimize resonance effects which help to increase the volume of air moving into each cylinder. To smooth airflow as much as possible at high rpm, the intake tract is nearly straight from the intake plenum chamber all the way to the intake port.

PROGRAMMED FUEL INJECTION (PGM-FI)

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 (PGM-FI) system uses a 16-bit microprocessor, which ensures that the correct amount of fuel is injected into each intake port at the proper moment.

COOLING

To meet the increased cooling requirements of the more powerful GS-R engine, a new radiator was used, similar in design to the radiator of the NSX. The core of the radiator is aluminum, for reduced weight and improved heat dissipation. The radiator top and bottom sections are molded of high-temperature resin, for reduced weight.

The GS-R engine also uses a special liquid-cooled oil cooler in which engine oil is routed through a heat exchanger that uses coolant from the radiator to extract heat.

TRANSMISSION

The GS-R is equipped with a special 5-speed manual transmission. All forward ratios, and the final drive ratio, are shorter (numerically higher) than in the standard Integra transmission, complementing the higher power peak and redline of the GS-R. Dualcone synchronizers are used for second gear, and even reverse gear is synchronized. The synchronizers for second, third, fourth and fifth gears are larger in diameter than in the standard Integra 5-speed, to accommodate the greater power output of the GS-R engIne.

The GS-R is fitted with a special lightweight fly wheel with 14% less rotational inertia, for quicker revving and enhanced throttle response.

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