1991 ACURA NSX Service Repair Manual

Outline

Description

This engine is a 2,977 cm3 (181.6 cu-in) DOHC mid-ship unit having 6 cylinders of 90° —V configuration; it is water cool-

ed and equipped with a center plug type pent roof combustion chamber. It is specified for unleaded fuel and uses a

PGM-FI system: The PGM-FI system on this model is a sequential multiport fuel injection system.
PGM-FI system. This engine incorporates a new mechanism called Honda Variable Valve Timing and Valve Lift Elec-

tronic Control System (VTEC). This mechanism, the world's first, allows the timing and lift of the intake and exhaust

valves to be changed simultaneously. The engine also includes a new electronically-controlled intake manifold system

that can change the volume of the intake chamber.ProCarManuals.com

This engine has the following new features.

Type

Displacement
Bore x Stroke
Compression Ratio
Cam, Valve Mechanism
Valve Train
Fuel Supply System Water-cooled V6—90° Cross Flow
2,977 cm3(181.6cu-in)

90 x 78 mm
(3.54
x
3.07
in)
10.2
Dual Overhead Camshafts, VTEC Belt Driven
Sequential Multiport Fuel Injection (SFI)VTEC; High output and a broad power band is achieved through control of low-speed and high-speed valve operation
by the Engine Control Module (ECM).
(Two knock sensors are used to detect octane level of the fuel.)
Titanium connecting rods ; Accomodate high rotation speed and high output. Titanium material of light weight and
high strength is used for the connecting rods.
(Strength is at the same level as iron.)
(Weight is about 30% lighter than iron.)
New mechanism to the intake system; Increased low and middle speed torque and higher output can be achieved by
switching the chamber volume of the intake manifold according to engine speed. This is electronically-controlled.
Cooling system for the mid-ship engine:
Radiator located in front compartment (An aluminum alloy radiator and pipes made of aluminum alloy)
Engine room cooling fan
Expansion tank
The cylinder block is highly rigid with deep water jackets. In order to achieve lighter weight, magnesium is used for the following parts: Cylinder head coverIntake manifold cover
Intake manifold chamber
Major SpecificationsProCarManuals.com

Variable Valve Timing and Valve Lift Electronic

Control System (VTEC)

Outline

The engine is equipped with multiple cam lobes per cylinder, providing one valve timing and lift profile at low speed and a
different profile at high speed. Switch-over from one profile to the other is controlled electronially, and is selected by monitoring current engine speed and load.

CAM LOBES FOR LOW RPM
CAM LOBES FOR HIGH RPM
PRIMARY ROCKER ARM
MID ROCKER ARM
SECONDARY ROCKER ARM
LOST MOTION ASSEMBLY
INTAKE VALVE
EXHAUST VALVEProCarManuals.com

In general, it would be ideal if the high rpm performance of a racing engine and the low rpm performance of a standard
passenger car engine could be combined in a single engine. This would result in a maximum performance engine with a
wide power band. Two of the major differences between racing engines and standard engines are the timing of the in-
take/exhaust valves
and the
degree
of
valve
lift.
Racing engines have longer intake/exhaust
timing
and a
higher valve
lift

than standard engines. The Honda Variable Valve Timing and Valve Lift Electronic Control System takes this into ac-
count.
When
valve
actuation
is set for low rpm
timing
and
lift,
low rpm
torque
is
better
than
in a
standard
engine.
When
valve actuation is then switched for high rpm timing and lift, output improves to the level given by a racing engine. Untilnow, few variable valve timing systems have been commercialized. In those that have, only the time that both valves are
open (intake/exhaust overlap) could be changed. Honda's system is the first in the world in which both the valve timing
and the degree of valve lift can be changed as needed, making it the most advanced valve train mechanism available.
Valve Timing
(exhaust/intake) Valve Lift Racing Engine

Exhaust Intake
VTEC Engine

Low High Low
Exhaust Intake
Standard Engine

Exhaust Intake

Max. Power

Low rpm Torque
Idling Stability

TDC = Top Dead Center

Low rpm

High rpm
VTEC engine
RPM switch over

point
Standard engine

rpm

BDC = Bottom Dead Center
O = Optimum Characteristic

The engine is equipped with two valve timing and valve lift settings which change according to driving conditions.ProCarManuals.com

Cylinder Head

Camshaft

The camshaft is a cast piece. By improving dimensional accuracy, it became possible to achieve minimum space be-

tween cams, thus allowing a more compact cylinder head. Each camshaft is supported on four bearing journals with forc-

ed lubrication. On the right end of each camshaft is a driven pulley. The exhaust and intake cycles require a total of 36

cam lobes to open and close the valves.

FRONT BANK

No. 6 No. 5 No. 4

S M P S M P S M P

P M S P M S P M S
EXHAUST INTAKE

S M P S M P S M P

P M S P M S P M S
REAR BANK

No. 3 No. 2 No. 1

No. 3 No. 2 No. 1
No. 6 No. 5 No. 4
INTAKE EXHAUST

P: PRIMARY

M:MID

S: SECONDARY

: Intake valve open

: Exhaust valve open
Manual Transmission

Automatic Transmission

Low-speed valve timing

High-speed valve timingProCarManuals.com

Lubrication System

Lubrication Flow

VTEC SOLENOID VALVE

ROCKER SHAFT

ORIFICES
M
M

M

CYLINDER HEAD

ORIFICE

OIL SCREEN

OIL PUMP

RELIEF VALVE

OIL FILTER

ENGINE COOLANT

ENGINE OIL

COOLER

CYLINDER HEAD

ORIFICE

ROCKER SHAFT

ORIFICES

P: PRIMARY

M: MID

S: SECONDARY
M
M

M

VTEC SOLENOID VALVE
No. 3

M
M
M
No. 1

No. 2
M

M
M

No. 6 No. 5 No. 4
Front

Rear
CRANKSHAFT

MAIN JOURNAL

MAIN BEARING

CAP BRIDGEProCarManuals.com

Exhaust System

Dual Exhaust System

A compact dual exhaust system is used to provide low back pressure.
Sound tuning has been optimized to give a sporty exhaust sound note suitable to this type of car. This is done by a col-
lection chamber in muffler.
MUFFLER

REAR
EXHAUST

PIPE

REAR EXHAUST

MANIFOLD

FRONT THREE WAY CATALYTIC

CONVERTER

REAR THREE WAY CATALYTIC

CONVERTER

FRONT
EXHAUST

PIPE

FRONT EXHAUST

MANIFOLD

Exhaust gas
from
rear bank

COLLECTION CHAMBER

Exhaust gas

from

front bank

FeaturesProCarManuals.com

Cooling

Cooling System

Two cooling systems are employed:

An antifreeze/water system with the radiator mounted in the front of the vehicle.

An air-cooling system driven by a fan mounted in the engine compartment.

BLEEDER

RADIATOR

BLEEDER

WATER VALVE

HEATER CORE
DRAIN

DRAINS

BLEEDER

ENGINE DRAIN

WATER PUMP

ENGINE OIL

COOLER

ENGINE DRAIN

FAST IDLE THERMO VALVE

IDLE AIR CONTROL (IAC) VALVE

BREATHER PIPE

THROTTLE

BODY
THERMOSTAT
TEMPERATURE SWITCH
ENGINE COOLANT
BLEEDER
EXPANSION

TANKProCarManuals.com