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Rotary engine
highlight "89 RX-7 changes

terference from the exhaust of the
other rotor. This results in reduced
turbo lag and increased torque.
The wastegate on the Turbo is
now electronically-controlled,
allowing finer regulation of boost
pressure under

pressure increasing interaction be-
tween the front and rear rotors.
Immediately downstream of the
throttle valve,
branches off to the two rotors.
Further downstream,
rotary valve connecting the two

THE 1989 Mazda RX-7 models
feature a number of refinements,
including improved power and fuel
economy from their unique rotary intake tract

The heart of any sports car is its
engine, and in the case of the
RX-7, that heart is the durable and
reliable 13B rotary engine. For
1989 the normally-aspirated engine
delivers 160 brake horsepower at
7,000 rpm and 140 ft.-lbs. of tor-
que at 4,000 rpm.

The turbo-charged powerplant
generated 200 brake horsepower at
6,500 rpm and 196 ft.-Ibs. at 3,500
rpm. These increases are the result
of improved inta!
compression ratios, lighter rotors
and, in the case of the Turbo, a
revised Twin-Scroll turbo-charger.

The normally-aspirated 13B-EGI
engine makes use of Mazda’s ad-
vanced variable dynamic effect in-.
take system, which utilizes pressure
waves generated within the intake
tracts to force more air into the
combustion chamber. This is ac-
complished by maximizing

During engine operation,
flows through these tracts at high
speed when the intake ports are
these ports are
abruptly closed by the rotor, the
inertia of the air in the tract creates
a high pressure wave which then
bounces off the ports and moves
back up the tract. This pressure
wave travels back to the tract
leading to the other rotor, increas-
ing the air pressure in that tract
and forcing more air into the
combustion chamber.

The effect of these pressure
waves is determined by the length
of the intake tracts. At higher
engine speeds a shorter tract max-
imizes the pressure effect, while at
lower speeds, a longer tract is re~

stems, higher

The rotary valve between the
two intake tracts effectively
changes the length of the intake
runners, remaining closed below
4,500 rpm to let the pressure waves
travel back to the point where the
intake manifold branches off. At
speeds above 4,500 rpm, the valve
opens, shortening the intake tract.
The overall effect is enhanced tor-
que, especially in the higher rpm
ranges.

To further improve the response
and output of the engine, the
rotors are 5 per cent lighter and the
flywheel is 16 per cent lighter. This
reduces the rotational mass and
allows the rev limit on the nor-
mally-aspirated engine to be rais-

The recesses in the rotors are
now machined and shallower, rais-
ing the compression ratio from
9.4:1 to 9.7:1 in the nor-
mally-aspirated models and from
8.5:1 to 9.0:1 in the Turbo.

The airflow meter has been
changed to a linear type for reduc-
ed air resistance and more precise

31 - Friday, May 12, 1989 - North Shore News

improvements

measurement. The engine
Management computer has been
upgraded to respond quicker to
throttle inputs and the caiculating
speed of the computer has been
doubled.

In addition, the computer can
‘earn’? the engine’s operating
conditions and optimize the
amount of fuel injection for im-
proved fuel efficiency and stable
idling.

An electronically-controlled oil
pump is used on both engines for
more effective lubrication
throughout the operating range.
This new pump also reduces oil
consumption significantly.

In the Turbo model, a complete-
ly independent twin-scroll turbo-
charger has been adopted. With
this design, the exhaust ports are
directly connected to each of the
two scrolis of the turbo-charger
impeller.

This permits the powerful ex-
haust pulse generated by the open-
ing of the exhaust port to directly
hit the turbine blades without in-

varying engine
conditions, thus improving both
torque and response throughout
the rpm range.

As a result of these changes, the
Turbo engine delivers maximum.
torque at speeds between 2,000 and
5,000 rpm, dramatically improving
the car’s performance and
driveability.

In addition to the changes under
the hood, a number of other
refinements have been made to the
1989 RX-7s.

The aerodynamic: have been

high-speed stability. The frontal
lift (CL£) of the Turbo has been
teduced from 0.13 to 0.06 and the
rear lift (CLr) from 0.01 to 0.007,
without affecting the overall 0.31