Mazda 12A Turbo
The 12A turbo engine was only sold in the Japanese market.
(Note, this information was sent to me from a fellow rotary
enthusiast. I think it is from the Yamaguchi book).
The TURBOCHARGED and fuel-injected 12A has been confined to the Japanese market, powering the first Cosmo and Luce cars starting in late 1982 and (in it's uprated version) the P132 RX7 from September 1983 through to the end of it's model life.
The 12A Turbo was the first production turbocharged and electronically fuel injected rotary engine.
In it's turbo guise the 12A reverted to four side intake
Air and fuel mixing is promoted at lower speeds by an air bleed to the injector nozzle receptacle, at higher rpm by a mixing plate socket, an open-sided plastic tube with twin perforated plates. The plates splash and squeeze injected fuel, aiding mixture atomisation.
The fuel injection control unit is an analogue type made
by Nippon Denso; it works in conjunction with a Mitsubishi Electric digital emission
Primary intake-port timing is unchanged from the carburetted
6PI engine: opening at 58degrees ATDC and closes at 40degrees ABDC.
Of interest in the air-only secondary intake port and
manifold are dual throttle valves.
The 12A Turbo was originally boosted by a Hitachi HT18-BM
turbocharger with a 62mm diameter, 11-blade turbine and a 63mm 12-blade
compressor supplying a relatively modest maximum boost of 320mm Hg (6.2
psi); Typical for a Japanese Turbo piston engine is about 400mm Hg (7.75
The 1982 12A turbo produced 160 BHP JIS at 6000 rpm, and a maximum torque of 224 Nm (165 lb-ft) at 4000 rpm; 15-20% should be deducted to get the approximate SAE net values.
Later, the engine was given a new turbocharger, Hitachi's HT18S-BM, with a smaller 57mm turbine and a 56mm compressor, it was dubbed an "Impact Turbocharger" by Mazda engineers because it fully exploited the rotary's forceful exhaust-gas impact with it's new turbine blade shape. The new turbo added 5 more horsepower to the engine's output, as well as improving low-end torque characteristics and minimising turbo lag.
The 12A turbo also has a knock-prevention system. Mazda
engineers found in developing the engine that knocking would only occur
under certain operating conditions: in a 2500-3750 rpm zone when intake
temperature exceeds 85 degrees celcius.
As the turbo rotary's performance and consequently the
thermal loads have been considerably increased (for the latter some 30%),
lubrication of the trochoid sliding surface and turbocharger has become
The 12A turbo engine (with all manifolds, turbo, fan, alternator, power steering and air-conditioning pumps) is 786mm long, 548mm wide and 638mm tall (30.9 x 21.6 x 25.1 inches) and weighs 162 kg (356 lb)
While now ancient history (2006), 12A turbo engines were quite popular in the late 1980s/Early 1990s due to their reasonable pricing and easy installation. The potential of these engines is fairly modest compared to the later 13B turbo engines.
These engines quite literally bolt straight into an early RX7. A stock
non-turbo RX7 5 speed gearbox would probably be OK with a standard engine,
but a slightly stronger gearbox was used with the 12A turbo motor. These
gearboxes also bolt straight in.
The stock power is around 160BHP (depending on what measurement
units (PS/JIS/SAE) are used ).
12A turbo engines seem to run successfully on virtually any injection computer around, so unless you have a complete wiring loom, airflow meter and computer it's probably going to be easier to use an aftermarket computer. Besides, the factory trapdoor airflow meter these engines used belong in the stone age, and are easily damaged by backfires. It seems the standard distributor based electronic ignition works acceptably.
As with any turbo engine the oil and water temperatures should be kept down.
I haven't seen much more information than this anywhere.
Further reading and acknowledgements:
Other relevant reading at Craig's Rotary Page (Please go via the INDEX
Other relevant sites on the Internet (Please go via the LINKS
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This page last updated 6/5/2006
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