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Mazda 13G (3 rotor engine)

Introduction / 13G-Racing / 13G-Production prototype / More Information


3 Rotor engines Introduction

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 gear/bearing)
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 - racing engine

13G (RACE) picture (640x480)
13G race engine (640x480)
(Bigger version - 1024x768)
13G (RACE) components (640x480)
13G race engine parts (640x480)
(Bigger version - 1024x768)
13G (RACE) 2nd intermediate (640x480)
13G race engine centre bearing
640x480
13G (RACE) cross section (640x480)
13G race engine cross section
640x480
13G (RACE) japanese specs (640x480)
13G engine specs (Japanese)
280x480
Source of these pics (640x480)
Source of these pictures
340x480

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 tapered section.
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.

13G Racing Engine specifications
Origin Based on early 80's 13B
Capacity 654cc x 3 rotors = 1962cc
Compression ratio 9.4:1
Induction Naturally aspirated peripheral port, electronic fuel injection (2 injectors per rotor)
Exhaust Peripheral Exhaust Port
Ignition Distributorless CDI ignition (2 plugs/rotor)
Power/RPM 450ps@8500rpm
Torque/RPM 40kgm@8000rpm
Max RPM 9500 RPM (Optimum 6000-9000rpm)
Dimensions Length 675mm Width 549mm Height 520mm (Complete engine)
Weight 143kg (Complete engine)
Special Features Dry Sump


13G - prototype production engine

13G prototype prodution engine picture (640x480)
13G "Prototype production" engine (640x480)
13G prototype prodution engine cross section picture (640x480)
13G "Prototype production"
engine cross section (640x480)
Mazda MX-03 concept car - 1984  (640x480)
Mazda MX-03 concept car
(Year: 1984) (640x480)
Mazda MX-03 concept car brochure (320x480)
Some of These pictures from
Mazda MX-03 concept car
brochure (320x480)

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 show)

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.

13G "Production Prototype" Engine specifications
Origin Closely based on early 80's 13B
Capacity 654cc x 3 rotors = 1962cc
Compression ratio (Unknown)
Turbo Boost (Unknown)
Induction Turbocharged (single turbo)/intercooled, electronic fuel injection
Exhaust Peripheral Exhaust Port
Ignition Distributorless electronic ignition (2 plugs/rotor)
Power/RPM 320ps@7000rpm
Torque/RPM 40kgm@3800rpm
Max RPM (Unknown, probably as for 13B of the time) MX-03 Tacho scale ends at 12,000
Dimensions (Unknown)
Weight (Unknown)
Special Features Dry Sump


More Information

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 1990-1996).
Racing Beat sell 13G parts, but price would be "on application".

Further reading and acknowledgements:
* Special thanks to Mr Nishizawa in Japan for sending me the LeMans and MX-03 items
* I have not seen any other information about this engine or the MX-03 in any books

Other relevant reading at Craig's Rotary Page (Please go via the INDEX page):
* World's fastest rotary page (Racing Beat Bonneville RX7 900hp triple turbo peripheral port)
* 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 page):
* Asmic's page has some pictures of the 13G engine


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This page last updated 16/3/2001
Update History:
16/3/2001 - Converted all text to new standard (Headings as Heading1, Some sub-headings (e.g. tables) as 14 point normal bold italic, Most text as Normal, Internal page links at top not all uppercase)
11/3/2001 - Changed from Netscape to FrontPage and from EWK2.HTM to PG19.HTM (& all sub files). EWK2.HTM changed to redirection page. Background image changed to PG00_02B.JPG
3/10/1997 - Previous known update (May have been some before this)

Special thanks to Mr Nishizawa from Japan
for sending me some info, and to
Tikuzen
for helping translate it for me!!

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