1995 Acura Integra- Powertrain
The Integra features two distinct engines. The RS, LS and Special Edition models offer an all-aluminum, 1.8-liter, DOHC, 16-valve, 4-cylinder engine. This engine, while similar to that of the second-generation Integra, has undergone a number of refinements to improve reliability and durability, improve efficiency and provide smoother power delivery. Among these features are the use of an axial-flow air cleaner, which reduces restriction 20%, and an eight degree change in the angle of the fuel injectors, for improved driveability and engine response. This engine produces 142 horsepower at 6300 rpm, and 127 lbs-ft of torque at 5200 rpm.
The GS-R model features a 1.8-liter engine equipped with the Variable Valve Timing and Lift Electronic Control (VTEC) system pioneered in the Acura NSX. It also features Programmed Fuel Injection (PGM-FI), a dual-stage intake system, a knock sensor, a crankshaft reinforcing bridge, oil jet piston cooling and a number of other innovations to improve reliability and durability, and to provide smoother operation. All this adds up to 170 horsepower at 7600 rpm and 128lbs-ft of torque at 6200 rpm. These impressive figures give it one of the highest specific output of any normally aspirated engine sold in the U.S., and its relatively long stroke and high redline give it the highest piston speed of any automobile engine in the world, even faster than the latest Formula One engines.
Variable Valve Timing and Lift Electronic Control (VTEC) System
The VTEC system, first pioneered in the Acura NSX and introduced in the 1.7-liter engine of the Integra GS-R, has been further refined in the current-generation Integra GS-R. As the performance of the NSX has already amply demonstrated, VTEC is an innovative solution to an age-old automotive engineering problem. It elegantly solves the trade-off between tuning an engine for either high-end horsepower or low-end torque. With VTEC, Acura engineers no longer have to compromise between the two. VTEC-equipped engines can have the best of both, especially when the system works in conjunction with the dual-stage intake manifold.
The VTEC system uses three cam lobes and three corresponding rocker arms for each pair of valves. The VTEC system operates on both the intake and exhaust valves. The two outer cam lobes have a profile that optimizes low-speed torque and response. The middle lobe has a high-lift, longer-duration profile that is designed to optimize high-end horsepower.
At low rpm, the middle rocker arm is idle. At a predetermined engine load and speed, the middle rocker arm is activated by means of a computer-controlled hydraulic piston, which locks all three rocker arms together. The middle rocker arm forces the two outer rocker arms to follow the higher lift and longer duration profile of the middle cam lobe, allowing the engine to draw and expel more air and consequently produce more power. This simple, yet elegant, design has proven its effectiveness as well as its reliability in both the NSX and the previous generation Integra GS-R.
In the previous GS-R, the changeover point between low lift and high lift was 5600 rpm. In the second-generation GS-R, the changeover point has been lowered to 4400 rpm, to enhance midrange torque and to fully exploit the benefits of the dual-stage intake manifold. By carefully balancing the 4400-rpm VTEC changeover point and the 5800-rpm opening of the second intake runner of the dual-stage intake manifold, the GS-R has an almost flat torque curve from 2500 rpm to 7200 rpm. This change makes the GS-R engine more responsive under all operating conditions, and especially when going from part-throttle, steady-state cruising to full throttle.
The GS-R engine utilizes the latest combustion technology to provide a combination of fuel efficiency and power. By carefully redesigning the combustion chamber, the engineers were able to lower the surface-to-volume area of the chamber.
By exposing less surface area to the heat of combustion, more heat is retained in the expanding gases, resulting in increased thermal efficiency. And the "squish" area around the combustion chamber is also increased, yielding increased gas turbulence, faster flame propagation, and even better efficiency.
The angle of the fuel injectors has also been changed by eight degrees, pointing more directly at the center of the intake valves. This reduces fuel condensation on the intake port walls, improving driveability and engine response.
Dual-Stage Intake Manifold
The dual-stage intake manifold on the GS-R engine features two intake runners for each cylinder, one longer than the other. When operating under 5800 rpm, only the longer of the two runners delivers air to the cylinder. Above 5800 rpm, a butterfly valve in the bore of the short runner opens to allow the passage of additional air to the cylinder. This has the desired effect of boosting midrange and high-end power output.
Pistons and Connecting Rods
In conjunction with a lightweight piston design, the GS-R engine also uses a newly developed connecting rod design. Constructed of high-strength steel, this connecting rod is thinner and lighter than a conventional connecting rod, yet it's 26% stronger.
The combination of lightweight pistons and connecting rods helps to reduce reciprocating inertia and enhance throttle response significantly.
Oil Jet Piston Cooling
To help ensure long-term durability and reliability, the GS-R engine uses an oil jet cooling system. A jet of pressurized engine oil is directed to the underside of the piston to help dissipate the extreme heat generated during sustained high rpm operation. This technology has proven itself in Formula One and other top-level racing engines.
Surface-Oriented Crystal Bearing Material
The use of a surface-oriented crystal bearing material was pioneered in Formula One racing and has been adapted for use in the GS-R VTEC engine. Unlike the surface of conventional bearing material, the crystal bearing surface has molecules oriented into a pyramid shape. This surface traps a layer of oil and holds it far better than conventional bearing surfaces, reducing friction and enhancing reliability. The load-resistance properties are so significant that the width of the bearing has been reduced 2 mm, but the load resistance has been improved by 35%.
5-Speed Manual Transmission
The Integra features two different manual transmissions. The transmission used in the GS-R model features different ratios, bearing design, clutch, flywheel, second, third and fourth gear synchronizers and reverse idle gear than the transmission for the RS, LS and Special Edition engines. The differences were necessary to handle the higher output of the GS-R engine, to ensure durability and reliability and to maximize fuel economy.
The main design goals of the GS-R transmission were to take advantage of the additional low- and midrange power and to enhance the GS-R engine's response without excessive rpm in freeway driving. The ratios of the GS-R transmission are roughly 7% taller than the previous-generation GS-R ratios, for increased fuel efficiency and quieter operation.
To reduce shift stroke, enhance driving fun and improve shifting precision, all manual-equipped Integra models feature a newly designed shift linkage. The shift stroke has been reduced 12 mm and shifter rigidity has been increased by 200%. The new system approaches the quality feel and short stroke of the Acura NSX shift linkage system.
Both manual transmissions feature a newly developed hydraulic clutch unit to provide progressive engagement and low clutch-pedal effort.
As in the past, all Integra models feature equal-length halfshafts, which virtually eliminate torque steer.
Electronically Controlled 4-Speed Automatic Transmission with Grade Logic Control System
The optional, electronically controlled 4-speed automatic transmission, available in RS, LS and Special Edition models, is a highly refined unit designed to offer a superb blend of sporty response and sophisticated manners. It features an ignition retard system to reduce shift-shock, a torque-load control shift sequence, a low-hold feature to enhance performance on driver demand, a large-capacity torque converter to reduce slippage and provide a more direct feel, and the newly developed Grade Logic Control System to reduce unwanted shift hunting on up- and downhill grades.
In conventional automatic transmissions, driving on a grade at a steady, partial throttle setting often causes frequent shifting between third and fourth gear. This is due to the fluctuations in the vehicle speed and throttle opening as it crosses into and out of the speed and throttle opening thresholds established for each gear in the transmission.
In operation, Grade Logic Control compares the actual driving condition with a map stored in the ECU (electronic control unit) memory. Based on the degree of variance between actual driving conditions and the map, the system either allows shifting or prevents it, in order to minimize frequent gear changes. In essence, the Grade Logic Control can estimate the grade of a hill by measuring the vehicle speed and throttle angle and comparing these to the map in the ECU. The system holds the transmission in a lower gear for better uphill acceleration and also provides additional engine braking in downhill driving.