OVERVIEW
The Integra features two distinct engines. The RS, LS and GS
models
offer an all-aluminum, 1.8-liter, DOHC, 16-valve, 4-cylinder
engine.
This powerplant produces 140 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 128 lbs-ft of torque at 6200 rpm. These impressive figures give it one of the highest specific outputs of any normally aspirated engine sold in the U.S.
VARIABLE VALVE TIMING AND LIFT ELECTRONIC
CONTROL (VTEC)
SYSTEM
The VTEC system, first pioneered in the Acura NSX, works
similar
performance magic in the 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.
The changeover point between low lift and high lift in the GS-R is 4400 rpm, for excellent 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 makes the GS-R engine 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. Because of the low surface-to-volume area of the chamber, minimal surface area is exposed to the heat of combustion and 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.
Also, the fuel injectors point almost directly toward the center of the intake valves, helping to reduce fuel condensation on the intake port walls and 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 sophisticated 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.
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 GS 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. All manual-equipped Integra models feature a short-stroke shift linkage of exceptional rigidity. The system approaches the quality feel and short stroke of the Acura NSX shift linkage system.
Both manual transmissions feature a refined 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 GS 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 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.