Mazda have made several prototype and experimental engines
over the years ranging from the 6A (a single rotor version of the 12A,
intended for use in Japanese "Kei" cars), the 2002 "4 rotor
10A" to the massive R-II 21A with 2x1046cc rotors
Several 3 rotor prototype and racing engines have been
produced over the years. Generally speaking these engines were constructed
using the modular nature of the rotary engine (that is to say, the parts
can be "stacked" together).
This allowed comparatively cheap production items (rotors, rotor housings,
side housings, seals etc) to be used in conjunction with some specially
made (expensive) parts (eccentric shaft and centre housing with rotor phasing
There has been only ONE passenger car 3 rotor engine - the 20B, which was
a twin turbo fuel injected engine.
Generally speaking, the following 3 rotor engines were
"available" from the early 1980s:
13G Racing engine (1984-1989), 13G "Production Prototype" (1984/1985),
20B Production engine (1990-1996), 20B Race engine (1990-now)
13G race engine parts (640x480)
(Bigger version - )
13G race engine centre bearing
13G race engine cross section
13G engine specs (Japanese)
Source of these pictures
This engine was produced around 1983/1984 for the 1984
LeMans 727c race car, and was used until about 1989.
The engine was based on the 13B engine of the time, with some special parts:
*Special centre housing with phasing gear
*Eccentric shaft to suit the 3 rotor design
*Different front housing (which has holes for the tension bolts to go through,
as the tension bolts screw into the special centre housing).
*The rotor housings were the type with the water seal groove. (But, the
external shape of the housings is narrower than the 13B)
*Most other parts, while virtually identical to the 13B, were custom-made
for this engine
The eccentric shaft used was a new design not previously
tried by Mazda. Previous designs were made from modified 2 rotor eccentric
shafts joined together with bolts and keyways, which were not rigid enough
for extended periods of reliable operation.
Essentially it was a 2 rotor shaft with a long extension on the front of
it that went all the way to the front pulley. Then for the front rotor
there is an eccentric shaft "sleeve" which slides over the front extension
on the eccentric shaft until the angled section of the main eccentric
shaft meets the corresponding section in the "sleeve" (Just like
the flywheel does in any Mazda rotary).
The bearing/spacer/bolt down plate used to adjust the backlash (as in any
Mazda rotary) performs the task of pushing the extension sleeve onto the
The extension sleeve is indexed (so the rotor is in the correct phase with
the other rotors) by a small keyway.
NOTE: There was also a 4 rotor engine very similar to
this engine called the 13J It was made a few years later that the 13G - see my 4 rotor engine
page for details.
Some of These pictures from
Mazda MX-03 concept car
This engine was produced around the same time as the 13G
racing engine, for the MX-03 concept car (shown at the 26th Tokyo motor
This engine was similar in construction to the 13G race
engine, but it appears to use more standard 13B components. This indicates
that this engine may have nearly been a commercial reality.
In fact, the MX-03 was a more than just a show car; it was a prototype for a
high end luxury sports car, expense would have stalled the project but the later
Eunos Cosmo embodied most of the ideals of the MX-03.
(Unknown, probably as for 13B of the time) MX-03 Tacho scale ends at
13G engines are extremely rare (and expensive).
I think the 20B engine that Mazdaspeed (Japan) and Mazda Motorsports
(USA) sell is actually a 13G, however these are very expensive ($US 20,000+ for the core engine alone).
Realistically the only option if you want a 3 rotor engine is to get a
used 20B (which were a production item used in the Japanese Cosmo from
Racing Beat sell 13G parts, but price would be "on
Further reading and acknowledgements:
* Special thanks to Mr Nishizawa in Japan for sending me the LeMans and MX-03
* I have not seen any other information about this engine or the MX-03 in any
Other relevant reading at Craig's Rotary Page (Please go via the INDEX
* World's fastest rotary page (Racing Beat Bonneville RX7 900hp triple turbo
* 20B engine page (the 20B is a 3 rotor engine used in a production car)
* Eunos Cosmo page (20B powered car)
Other relevant sites on the Internet (Please go via the LINKS
* Asmic's page has some pictures of the 13G engine
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This page last updated 16/3/2001
16/3/2001 - Converted all text to new standard (Headings as
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3/10/1997 - Previous known update (May have been some before this)
to Mr Nishizawa
for sending me some info, and to Tikuzen
for helping translate it for me!!
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