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4 Rotor Engine info
(Mazda factory and aftermarket conversions)

Introduction / 3805 Engine / 2002 Engine / 13J Engine / R26B Engine / Aftermarket 4 rotors / More information


Four rotor engines have been even more of a dream for the average rotary enthusiast than three rotor engines. A four rotor engine is capable of incredibly smooth delivery of power, as smooth as or even smoother than a V12 piston engine. During the early days Mazda experimented with several three and four rotor engines, however due to cost and practicality reasons never produced any production versions, (except the 13J and R26B racing engines)

The Mazda 3805 four rotor engine.

The 3805 4 rotor engine was one of the early prototypes. Produced in 1963 it was a relative of the early families of rotary that would develop into the production 10A engines.
The 3805 was derived from the L8A engine (0353), which also had a 3 rotor variant, the 3804.
The 3805 was tested in a prototype sports car (designated R16A, by 400cc rotor displacement x 4 rotors = 1600cc, or "16").
The target power output was 160hp @ 7000rpm, phenomenal for a mid 1960s Japanese car, however there was no test results to prove this.

Mazda 3805 four rotor engine (640x480)
3805 four rotor engine
Mazda R16A four rotor concept car (640x480)
R16A concept car

The Mazda 2002 four rotor engine.

The 2002 was essentially two 10A motors joined together using a 'Curvic Coupling'.
It was produced in September 1971 which would imply being the type of 10A used in the R100 coupe. Power output was measured at 180hp@6000 rpm, with the engine capacity being twice that of a 10A (491cc x 4 rotors=1964cc), while the 10A of the time was making around 100hp, the 2002 was intended for a flagship sedan.
This engine would have been reasonably practical to manufacture due to the only special parts being the eccentric shaft made from modified stock 10A parts and the centre housing in the middle of the engine (which was wider to accommodate the coupling components of the eccentric shaft).

The main problem with the early forms of eccentric shaft coupling was that the were not sufficiently rigid to cope with continuous operation engine, as they were essentially two shafts with a spline to transmit the power and a bolt through the centre to hold the assembly together.
This problem was rectified in later multi rotor engines by having a single rigid shaft through the whole engine, with the rotor bearing lobes for the rear rotors as part of the shaft and the front rotor(s) using rotor lobes as an "auxiliary shaft" that slips over the top of the main shaft. See below for an explanation diagram, also see my 13G or 20B pages for a picture of this.

Mazda 2002 4 rotor engine (640x480, 1024x768)
2002 four rotor engine
Mazda 2002 4 rotor engine eccentric shaft (640x480)
2002 Eccentric shaft

(Note- the bottom eccentric shaft was from a prototype single rotor engine for Japan's "Kei" car class- possibly the X002, which was "half a 10A")

The Mazda 13J four rotor engine.

Mazda 13J-M 4 rotor engine (440x385)
13J-M four rotor engine
Mazda 13J-MM (possible 13J-L) 4 rotor engine (435x400)
13J-MM Engine (435x400)
(may possibly be 13J-L)
pg03_09c.gif (45213 bytes)
Eccentric shaft explanation

This engine was produced around 1988 and used until about 1990 when it was replaced by the R26B.
It was based on the 13G 3 rotor engine, which in turn was based on the 13B (2 rotor engine) of the time, with some special parts:
*Special centre housing with phasing gear
*Eccentric shaft to suit the 4 rotor design (see diagram above).
*13J engine has 4 bearings (in the front housing, the first and third intermediate housings and the rear housing). Unlike the 2002 engine with only 3 bearings for the eccentric shaft (quite acceptable for a road car, but undesirable in a racing engine).
*Most other parts, while virtually identical to the 13B, were custom-made for this engine (The only common parts with 13G/13B were the rotors and rotor housings)

There were several revisions of the basic engine design, with minor improvements each time:

(M = modified). 500bhp@8500rpm Peripheral port with fixed length intake trumpets, EFI, 2 plugs/rotor. Used in the 1988 LeMans 767 racer.

630bhp@9000rpm Peripheral port intake with variable length intake trumpets (2 steps only), EFI, 2 plugs/rotor. The 13J-MM has ceramic apex seals and the side housings were hot sprayed with a ceramic surface for wear&friction resistance. Used in the 1989 LeMans 767B racer.

Much the same as the 13J-MM Used in the 1990 LeMans 767B racer.

The R26B four rotor engine

The R26B four rotor engine was developed for Mazda's racing program in 1990.
It was an all new design derived from the 13J engine (specifically the 13J-MM), but with few interchangeable parts.

The major differences from the 13J are:
* Three spark plugs per rotor-The additional one at the top is called a "late trailing".
* The variable length intake trumpets were multi-step in the 1990 R26B, continuously variable in the 1991 version (for maximum possible torque at any RPM).
* The rotor housings and side housings were hot-ceramic coated

The LeMan's specification engine produces 700bhp@9000rpm, 607Nm/448ftlb@6500rpm, and engine capacity is 654cc x 4 rotors=2616cc
The Mazda LeMans 787B racer powered by this engine won LeMans in 1991, the making both the first Japanese manufacturer and the first non-piston engine to win.

Acceleration of the 787B is impressive, as it weighs 800kg, giving it a power to weight ratio of 1.2kg/bhp (2.6lb/bhp).
As a comparison consider the following: Ferrari F40 2.6kg/bhp (5.7lb/bhp), Porsche 911 turbo 4.5kg/bhp (9.9lb/bhp)
This will allow a 0-100m (328ft) sprint in ~2.5 seconds, and a 1/4 mile with a terminal speed of 250km/h (155mph) - somewhere around 9 seconds!
(actually maybe about 10 or 11, as the car is not set up for drag racing)

Unfortunately the rotary was banned from European racing by FISA in 1992.

To a certain extent the USA's IMSA GTP series is very similar to LeMans style racing and the RX-792P carried the rotary flag for a while.
The R26B used in this car was down a little in power and torque, 650bhp@8500rpm, 570Nm/420ftlb@6500rpm

Mazda R26B 4 rotor engine (640x480, 834x575)
R26B Engine
Mazda R26B 4 rotor engine drawing (640x480, 1024x768)
R26B drawing
Mazda R26B 4 rotor engine (640x480, 1024x768)
R26B Engine
Mazda R26B 4 rotor engine parts (640x480)
R26B Engine parts
Mazda R26B 4 rotor engine eccentric shaft (640x480)
R26B Eccentric shaft
pg03_09c.gif (45213 bytes)
Eccentric shaft explanation
Mazda R26B 4 rotor engine variable intake (640x480)
R26B variable intake 
Mazda R26B 4 rotor engine (640x480, 1024x768)
R26B Engine

R26B Engine

R26B Engine

R26B Engine

Aftermarket 4 rotors:

Yashiro Iron Works
in Japan make components that convert 13Bs into "YR26B" engines. They use a built up eccentric shaft design and significantly there is a bearing on each side of each rotor (5 bearings vs 4 in the Mazda design)
Capacity 654cc×4
Maximum Power 500ps/8500rpm
Maximum Torque 40kg-m/8000rpm
Intake Peripheral port with downdraught Weber style carburettors
Dimensions 820×549×520(mm)
Weight 200kg

The power output of this engine is a bit less than might be expected, however this was done with simple carburettors and standard 13B spark plugs, none of the fancy variable intakes, EFI or triple spark plugs used on the factory engine. I also understand that the engine is a work in progress.

Update March 2005, from Jarle in Norway via email:
Thay have changed their name to Yashiro Engineering.
They do deliver 4 rotor eccentric shaft, and complete engine.
The price for complete engine, no electrical, ignition, or manifolds, carbs, injection.. is aprox 9000 euro.

Hurley engineering (England)
have also made 3 and 4 rotor engines from standard Mazda parts for many years. I visited there in 2001 but unfortunately much of the multi rotor work was not available for viewing. There is a Hurley page elsewhere on this site. Read there for further details.

I also understand there is an engineering company in New Zealand working on a 4 rotor engine. They have already made a 3 rotor engine so a track record is in place.

Jeff Bruce (New Zealand)
I sent a query Apr 06:
Hi Jeff,
I have a rotary website would you mind writing a paragraph about what services you can provide, pricing etc .. about 3 & 4 rotor engine suppliers and the only ones I know of are Hurley, Yashiro and yourself. Do you have a real working 4 rotor engine?

Hi Craig,
Basically we make driveline parts for race cars etc. Mainly flywheels, axles, pulleys and gearbox alterations (ratio changing etc) . The rotary parts have come mainly from my conversion to fit a front stationary gear into a centre housing which makes the three and four rotor engines a reality. There are lots of engines running around the world, mainly in drag cars it seems. Probably the most notable are some in Puerto Rico as one there is currently the second fastest rota in the world. In Australia the best there is (was) the "Barbie" car, which is a BMW 3 series with a turbo quad in it, has 1130 rwhp so they say (approx 1400 hp) at engine. There are a couple of pp quad engines here, a mate has a n/a one and another guy a turbo version. Also several are in the build at the moment. If you want any other bits let me know , there are a few videos around too so I'm told. regards Jeff Bruce

General Info on Rotary Kits 01/12/2005
This is a general list of parts available to convert Mazda 13b/12a type engines to 3 or 4 rotor variants, only the modified parts are listed as most others are Mazda items or are easily fabricated by a competent engine builder. All prices are in NZ$ and are ex factory so no allowances for shipping etc have been made . NZ customers should note that gst is charged on top of these prices.

1. 3rotor crank assy NZ$2200 (12a based version same price)
2. 4rotor crank assy NZ$3200 (includes special rear c/weight)(12a same price)
3. Centre housing modification for 3 or 4 rotor kits NZ$700 (2 req for 4 rotor)
4. Thru stud set (10mm) for 3 rotor NZ$225
5. Thru stud set (10mm) for 4 rotor NZ$245 (12mm also available)
6. Dowel set for 3 rotor kit NZ$120
7. Dowel set for 4 rotor kit NZ$150
8. Direct oil feed for 3/4 rotor kits centre housing NZ$90 (2 req for 4rotor) this mod is not a necessity only an upgrade for the oiling system.
9. Replacement 20B shaft assy NZ$2200.
10. 20b shaft assy , 3 piece with extra needle bearing assy NZ$3000 (3rotor version same price)
11. 13b/12a centre bearing crank kit NZ$1900

Note that the centre housing mod cost is only for the mod, it does not include the cost of a std front gear or the housing ,these items esp the housings vary greatly in price depending on the year/type. They can be priced on submission of version required.

Grannys speed shop (USA)
has made a 4 rotor engine for racing but they are not a production item. See links.

More Information:

Information about 4 rotor engines is very sparse

Further reading and acknowledgements:
* The first edition and second editions of 'RX7' by J. Yamaguchi
* Thanks to Asmic ( for the 13J engine pictures.
* Thanks to Lance ( for the first of the R26B pictures.
* Thanks to for the R26B pictures with the 55 car
* Thanks to Aero Rotary Engine Newsletter ( for the last two R26B pictures 

Other relevant reading at Craig's Rotary Page (Please go via the INDEX page):
* 13G Engine (3 rotor engine related to the 13J)
* Books (RX7 by J. Yamaguchi)
* Weird Ideas (Home made 4 rotor engine)

Other relevant sites on the Internet (Please go via the LINKS page):
* Asmic's page has some pictures of the 4 rotor engines
* has also has some R26B pictures
* Hurley engineering in the UK make 3, 4 and 6 rotor engines from standard Mazda 2 rotor parts
* Yahsiro Iron Works YR26B engine.
* Granny's speed shop has a page about joining two 13B engines.
* is working on a 4 rotor powered RX7
* Jeff Bruce in New Zealand email address precisin %
* 4 rotor engine in a BMW drag car

This page last updated 6/5//2006

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