Mazda has always stayed in touch with its buyers
and has been a leader in innovation.
In 1978 the first generation naturally aspirated 12A Rotary powered RX-7 or ‘Savanna’ in the local Japanese domestic marketplace, took
the world by storm, exceeding production expectations and causing traffic jams at the dealerships..
The 13B REW twin-rotor engine fitted to all third generation Mazda RX-7s can trace its origins to 1974 when Australians first drove the Mazda RX-4.
A lot has changed through the many years of development since then.
As fitted to the 1974 RX-4, the carbureted 13B produced 95Kw @6500 rpm and 174 Nm of torque @4000 rpm.Mazda-RX7-NA-Rotary-Motor-02
Later Rotary versions employed a unique sequential twin turbo system to produce 176 Kw at 6500 rpm and 300 Nm of
torque @ 5000 rpm.
Torque output was increased throughout the rev range with as much as 255Nm available at a low 2000 rpm.
Maximum RPM was been raised to 8000 and the rotor’s compression ratio of 9.0:1 necessitated premium grade unleaded petrol.
The Mazda Rotary engine
inherited the basic 13B geometry and epitrochoidal dimensions of
654 cc for each of its two rotors. However in 13B REW
configuration, many of the rotary’s major mechanical and
electronic systems received extensive modification. Among the
many internal upgrades were a thin wall cast-iron rotor with
fully machined combustion recesses to ensure uniform combustion.
Apex seal slots were hardened to resist wear. Modifications have
also been made to the aluminium rotor housing around the “hot
spot” spark plug area for more coolant flow. The engine’s
induction, exhaust, cooling and lubrication were modified or
redesigned when compared to the series V RX-7 engine.
Cooling and lubrication are vitally important to an engine producing the power the 13B REW. Both rotors are kept cool by splashing them internally with oil. Internal lubrication is via an electronically controlled metering system that reduces oil consumption by 25-50 per cent compared to the previous method of supply to the intake and trochoid chamber combined.
Lubrication is
fed under high pressure to the eccentric shaft bearings via a
high-efficiency multi port rotary pump. The heated oil is then
sent through two oil-coolers (one in each of the nose vents )
before being re-used. A lightweight aluminium and plastic
radiator, fully shrouded and slanted sharply to lower the RX-7’s
nose was fitted up front. Maintaining the correct temperature is
a pair of three stage thermo fans and keeping the flow is a
lightweight aluminium water pump.
The fire in the
new 13B REW was supplied by the world’s first volume-production
sequential twin turbocharger system. It produced more power than
a conventional twin turbo setup where both turbos boost at once,
and suffered far less turbo lag. The advantage of the sequential
system was the ability to utilise a small and large turbo at the
same time. At low rpm the 51mm diameter turbo with its “impact”
blade design spools very quickly, providing boost from as low as
1500 rpm. At a calculated point the second 57mm diameter turbo
is switched on, giving full boost all the way to the 8000 rpm
redline.
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