One of the most innovative engine designs of the
last 50 years is the Mazda rotary. With some major efficiency advantages over
traditional reciprocating engines, the rotary is capable of producing massive
power outputs from a modest capacity. It’s no wonder turbocharged versions can
produce well excess of 200kW.
In this article we’ll examine the late-model
rotary engines that provide plenty of power - with and without the assistance of
The most powerful production version of the Mazda
rotary is the 20B twin-turbo as fitted to up-spec versions of the Japanese
market JC-series (1990 – 1995) Cosmo.
Even by today’s standards, the 20B twin-turbo is
an absolute knockout. The officially quoted power output is 206kW but it’s
widely acknowledged that the actual output is around 220kW. And there’s ample
torque to go with the kilowatts – a maximum of 402Nm at 3500 rpm with over 390Nm
available from just 2200 rpm...
We’re talking V8 killer here!
The 20BTT delivers its punch thanks to an
effective combination of extra cubes and a sophisticated sequential twin-turbo
The 20B engine is a triple rotor design which has a total rotor chamber
volume of 2 litres. Interestingly, the 20B is essentially a twin rotor 13B
with another 654cc rotor chamber hung off the end. Those triple rotor
changers are boosted above atmospheric pressure thanks to a sequential
twin-turbo system that is intended to deliver a broad spread of torque. The
primary turbocharger provides meaningful boost pressure by 1800 rpm and the
secondary turbo kicks in at around 4000 rpm. The transition from single to
twin-turbo operation is kept smooth using a complex array of actuators and
pressure lines - the transition is much smoother than, say, a Subaru Liberty
B4. Maximum boost pressure is around 8.5 psi and charge-air temps are
chilled by a front-mount air-to-air intercooler.
Note that the 20B was produced in twin-turbo form
only – there was never an atmo variant. Like all Mazda rotaries, this engine is
configured for longitudinal mounting and, as far as we can determine, it comes
with a 4-speed auto only.
The 20B is always in high demand and, as a result,
you’ll pay quite a bit for one from the import wreckers. If you plan to
transplant the engine into another car you’ll need to ensure you buy a
half-cut rather than a bare engine – it’s almost impossible to configure the
twin turbos without the associated factory control system and ECU.
The second most powerful Mazda rotary is the 13B
twin-turbo as fitted to the FD Series 8 (1999 – 2002) RX-7 Type R and RS.
In Series 8 Type R and RS guise, the 13BTT makes dead-on 206kW at 6500 rpm.
The smaller capacity of this engine (1.3 litres total rotor chamber volume)
is a disadvantage compared to the 20B but it still makes bucket-loads of
torque - a peak of 314Nm at 5000 rpm and 280Nm from as low as 3000 rpm.
The Series 8 engine is the latest and greatest
version of the 13B twin-turbo which was first seen in the base-spec 1990 Cosmo.
The Series 8 Type R and RS engines produce their extra grunt thanks to altered
HT-12 turbochargers (which operate sequentially like on the 20B), slightly
increased boost pressure (up to 11 psi) and reduced exhaust backpressure. The
static compression ratio remains at 9:1. The performance of the front-mount
air-to-air intercooler is also enhanced by a redesign of the car’s nosecone to
provide greater cooling airflow. Five-speed manual or 4-speed auto transmissions
The Series 8 Type R and RS
engines are quite rare and so are very expensive. You’re much more
likely to find slightly less powerful versions at an affordable price.
The twin-turbo 13B fitted to the Series 6 and 7
RX-7 is rated at ‘only’ 187 - 195kW depending on production date, intended
market and transmission choice. The base spec JC-series Cosmo also uses a 13B
twin-turbo producing a surprisingly low 172kW. These are auto-only.
Again, if you want to run a 13B with an
operational twin-turbo set-up, your best bet is to buy a half-cut – this ensures
you have all the necessary hardware.
13B Single Turbo
Before the release of the sequential twin-turbo
13B came the single turbo version.
The single turbo 13B was first introduced in the
FC-series RX-7 of 1986. In early Series 4 versions, the 13BT delivers 136kW and
245Nm using a 8.5:1 static compression ratio, twin-scroll turbocharger and a
top-mount air-to-air intercooler. Manual or auto tranmissions were offered.
In 1988, the turbocharged 13B was also fitted to
the Japanese market Luce Limited and Royal Classic. We believe these engines are
non-intercooled and, as a result, make slightly less power – 132kW. The Luce 13B
turbo comes with an automatic transmission only.
The final incarnation of the single turbo 13B was
in the 1989 update of the FC-series RX-7 – the Series 5. The Series 5 engine
boasts a less restrictive intercooler, different rotors and a revised
turbocharger. The result is 151kW.
These single turbo 13B engines are becoming very
hard to source from Japan in good condition. You’re almost better off buying a
local engine that’s stuffed and having it rebuilt by a rotary specialist – at
least you’re assured some longevity.
When the Series 8 RX-7 was axed in 2002 it was the
end of Mazda’s affiliation with rotary engine technology. But not for long.
In 2003, Mazda released a dramatically
re-engineered version of the twin-rotor 13B known as the RENESIS rotary. The
primary goals of this major rework were to improve fuel consumption and emissions.
Compared to the original 13B, the RENESIS engine
has relocated exhaust ports, a variable intake manifold, new generation
injectors and electronic throttle control. With a high 10:1 compression ratio,
this engine can generate up to 184kW at 9000 rpm. Note how much higher a
naturally aspirated rotary needs to rev to achieve turbo-rivalling power...
Australian versions are detuned to produce 177kW or 154kW, depending whether you
select a manual or automatic transmission.
Fitted to the RX-8 only, the RENESIS rotary is not
yet available in significant numbers from Japanese import wreckers. You may be
able to find one in a crashed locally-delivered RX-8 - but don’t expect it to be