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Cosmo Sports/Mazda 110S and it's 10A engine

Introduction / Cosmo L10A / Cosmo L10B / Specifications / Sales brochure / Racing / 2002 Cosmo? / More information


The COSMO SPORTS, or for later export versions the MAZDA 110S was officially launched on 30 May 1967. The world's first two rotor production car, it beat even the NSU Ro80 to market by three and a half months (Note, Mazda paid NSU hefty licence fees for the use of the Wankel design. All Mazda rotor housings have "NSU licence" cast into them).

The start of the Cosmo project was in December 1962, with Mazda's first two rotor engine prototype in July 1963. The first prototype cars were produced by August 1963, and in October 1963 the head of Mazda, Tsuneji Matsuda drove the prototype known as 'Project L402A' to the Tokyo motor show. See picture below where they are returning from the motor show, judging by the smiles on their faces this car was a real hit!

This car used the prototype engine known as the L8A (or 0353), with 2x398cc and a combination of peripheral  and side intake porting.

The L8A evolved to the L10A (or 0810-pictured below), with 2 x 491cc and size intake ports. The peripheral ports were dropped* and the engine size increased to give better operating characteristics (Better torque at a lower RPM). All production Mazda rotary engines since have used side intake ports.

The prototype engines and cars progressed and in April 1966* a pre-production run using of 80 Cosmos were made (L10A engine), 60 of which were sent out as evaluation models to Mazda dealers in Japan, accumulating over 600,000km in 6 months.

The design was finalised in late 1966 and production would have commenced soon after for the 30 May 1967 launch date.

*Note 1: Regarding the date of the Cosmos going to dealers, one source says January 1965, while another claims April 1966.
*Note 2: One source claims the peripheral port intake was re-introduced for the final production engine, however I think this is incorrect.
Note 3: Most Mazda engines are known by a 'common' name such as L10A and an engine code name such as 0810

Cosmo type L10A and it's engine.

cosmo prototype returns from tokyo motor show (640x480)
Cosmo after Motor Show
Cosmo type L10A sketch (640x480)
Cosmo type L10A sketch
(640x480)(Also 640x480)
L10A cosmo final clay model (640x480)
Cosmo type L10A final clay
model for production (640x480)
Cosmo type L10A (640x480)
Cosmo type L10A
Cosmo type L10A dashboard (640x480)
Cosmo type L10A dashboard
L10A cosmo engine (type0810) (640x480)
L10A ('0810') engine
L10A cosmo production line (640x480)
Cosmo type L10A production
German Magazine Mazda Cosmo Sport L10A (640x214) (2069x692)
German Magazine L10A
German Magazine Mazda Cosmo Sport L10A (346x480) (1587x2200)
German Magazine L10A
German Magazine Mazda Cosmo Sport L10A (352x480) (962x1310)
German Magazine L10A
German Magazine Mazda Cosmo Sport L10A (640x480)
German Magazine L10A

N.B. 1587x2200 version of German magazine file to be fixed

The L10A name was shared by both the car and the engine.

While the car was mostly conventional late 60s sports car, it boasted several 'high tech' items, such a de-dion rear suspension, front disc brakes and an 'aircraft inspired' dashboard. (With Tachometer, Speedometer, Oil Pressure gauge, Water Temperature gauge, Ammeter and Clock).

The L10A Cosmo was only sold in Japan.

The engine is the main point of technical interest. Called the L10A (or 0810).
With 2x491cc rotors and 110 hp it featured the same Trochoid dimensions ('stroke') as nearly all production engines (10A/12A/13B/20B), meaning a 13B rotor would fit into a L10A rotor housing, except the 13B rotor is much wider.
Incidentally the only production Mazda rotary with different 'stroke' was the 13A, used in the Luce R130.

The rotor housings were hard chrome plated cast aluminium, the side housings were also made of cast aluminium (the only production Mazda rotary ever to use this), they were sprayed with carbon steel for wear resistance.

The rotor was made from cast iron and featured twin side seals and triple oil seals (today's 13B has a single side seal and twin oil seals). Apex seals were aluminium impregnated carbon - found to wear under 1.0mm in 100,000km driving. Before this "new" apex seal design the rotor housings had severe "chatter" marks, so Mazda was overjoyed to solve that problem. The eccentric shaft was made from expensive chrome-molybdenum steel.

Most of the other techniques used in the engine are standard practice today - oil spray to cool the rotors, oil cooler, gear type oil pump, oil metering pump to put a small amount of oil into the intake, axial flow water cooling etc. Ignition timing was Leading 2 degrees ATDC / Trailing 7 degrees ATDC

The engine weighed 102kg (225lb) and was 508mm long x 594mm wide x 544 mm high.

By 1967 standards the L10A Cosmo's performance was excellent. It's 400m/quarter mile time of 16.3 seconds is still comparable to some contempary cars (e.g. The 2001 MX5/Miata is 16.4 seconds over 400m).

Cosmo type L10B and it's engine.

L10B cosmo side shot (640x480)
Cosmo type L10B
L10B cosmo on speed track (640x480, 1024x768)
Cosmo type L10B
L10B cosmo front/side (640x480, 1024x768)
Cosmo type L10B
L10B cosmo rear (640x480)
Cosmo type L10B rear
L10B cosmo interior (640x480)
Cosmo type L10B interior
L10B cosmo engine (10A type 0813) (640x480)
L10B ('0813') engine

As with the earlier model, the L10B name was shared by both the car and the engine.

This model was started production on 13 July 1968.

The newer version of the Cosmo was slightly updated, with a 5 speed gearbox, power assisted brakes and optional air conditioning fitted behind the seats on the rear parcel shelf, the wheel base was lengthened by some 150mm (5.9 inches), which tended to make the car look more balanced. The car was also given a much larger radiator grille (probably to improve cooling). Larger 15 inch steel wheels were used. The overall weight was up by 50kg to 990kg.

The engine L10B (or 0813) had more power at 130 bhp, thanks to revised port timing and carburetion, however the basic internal design was unchanged. The air filter enclosure was modified to have two intake tubes, the earlier Cosmo only had one.

The L10B Cosmo was mostly sold in Japan, however as NSU granted Mazda a "world-wide" licence in 1968, a limited export program was undertaken. Due to the low volume/high costs the car was only sold to countries that had or allowed right hand drive cars, including France, Holland, Denmark, Belgium, Germany and Canada.

None were officially sold in Australia, however one was officially imported for evaluation and about 5 have been privately imported - see below for information about one on display in Melbourne.

Interestingly the exported cars were fitted with the earlier Cosmo's L10A 110hp engine, 4 speed gearbox, 14 inch steel wheels, presumably avoid maintenance troubles.
The export model was known as the MAZDA 110S (the 110 coming from 110 horsepower and the S meaning Sport)

With 130bhp (20 more than the earlier Cosmo), the L10B was even faster, it's 400m/quarter mile time of 15.8 seconds is comparable to sporty cars such as the 2001 BMW 330i at 15.9 seconds.


Cosmo Sports quick facts
Type L10A Type L10B
Start production
Stop production
Number made
May 30, 1967
July 1968
343 made
July 13, 1968
September 1972
1176 made
Price 1.48 million yen (=$US4100) 1.58 million yen (=$US4390)
Motor L10A
(engine code 0810)
(engine code 0813)
Motor design Alloy rotor housings
Alloy side housings
Side intake ports (2 per rotor)
Peripheral exhaust port

Same rotor dimensions as
all 10A/12A/13B/20B
(Only the width changes)


(but revised port timing for more power)

Intake Zenith-Stromberg 4 barrel
(but new 2 intake air cleaner housing)
Ignition Twin Distributor
Conventional points
Two spark plugs per rotor
Twin coils
Power 110 bhp@7000 128 bhp@7000
Torque 13.3 kgm@3500
(=96 lbft)
14.2 kgm@5000
(=103 lbft)
Capacity 491cc x 2 rotor Same
Compression 9.4:1 Same
Gearbox &
ratio (1st)
ratio (2nd)
ratio (3rd)
ratio (4th)
ratio (5th)
ratio (R)
Final drive
4sp Manual
(no 5th)
5sp Manual
Wheels &
14x4.5 Steel wheels
165 SR 14
15x4.5 steel wheels
155 HR 15
Unequal length "A" arms
Coil spring
Tubular shock absorber
Anti roll bar
51mm solid De-Dion
Semi elliptic springs
Upper trailing links
Brakes Front Disc/Rear Drum
No Assistance
Same, but with vacuum
servo assistance.
Steering Rack and Pinion
Adjustable steering column
Exhaust "Twin system" Same
Fuel Tank 57 litres (15 US gal) Same
Weight 940kg (2070lb) 990kg (2183lb)
Length x width
x height
4140 x 1595 x 1165 mm
(163.0 x 62.8 x 45.9 in)
4130 x 1595 x 1165 mm
(162.6 x 62.8 x 45.9 in)
Wheelbase 2200mm (86.6 in) 2350mm (92.5 in)
Air Conditioning Not Available Optional
Top speed 200 km/h (actual)
185km/h (Mazda advertised)
200 km/h (Mazda advertised)
Actual?? Maybe 220????
0-100 km/h 8.8 seconds 8.0 seconds (My estimate/guess)
1/4 mile 16.3 seconds
(at about 130 km/h)
15.8 seconds
(at about ? km/h)

Notes about the above table:

There are several "used car" magazines in Japan that occasionally have a Cosmo Sport advertised for sale. IF you can find one they cost around $US20,000 - $30,000 depending on condition. Other than that, I have NO IDEA where you would look for one!!

The 'De-Dion' axle arrangement can be thought of as being halfway between a conventional live axle and fully independent suspension - the differential is mounted to the car's frame, with allows less unsprung weight for better handling. The two wheels are solidly locked together by the de-dion axle. The two wheels are therefore not independent.

Regarding the L10A's slower top speed claim, 200 km/h (124mph) was the measured top speed, however Mazda de-rated this to "guarantee" 185 km/h (110mph), as well as be safer on the specified tyres.

Cosmo Sales Brochure

Mazda Cosmo Sport postcard (640x400, 1024x643)
Cosmo Sales "Postcard"
Mazda cosmo sales brochure (558x480) (893x768)
Brochure page 1 (558x480)(893x768)
Mazda cosmo sales brochure (559x480) (895x768)
Brochure page 2 (559x480)(895x768)
Mazda cosmo sales brochure (640x284) (1024x455)
Brochure page 3 (640x284)(1024x455)

They are original copies of sales literature for the Cosmo Sport. The postcard is of the earlier L10A model, and the Brochure is of the L10B model.
Please excuse the mis-match of the images in the brochure, the brochure was too large to fit in the scanner so I had to do it in several passes and paste them together in a paint package.

Racing Cosmos

L10A racing cosmos (640x480, 1024x768)
Cosmo type L10A Race cars
L10A race car at nurburgring (640x480)
Cosmo type L10A race car
L10A Racing motor (640x480)
L10A Cosmo racing motor

Mazda sent several L10A Cosmos to Nurburgring in Germany to prove the reliability of the cars and particularly the engine. I am looking for more details about this.

Mazda Cosmo 21

pg16_25b.jpg (54822 bytes)
Cosmo 21 (500x350)
pg16_26b.jpg (24178 bytes)
Cosmo 21 (500x350)
pg16_27b.jpg (59746 bytes)
Cosmo 21 (500x350)
pg16_28b.jpg (70601 bytes)
Cosmo 21 (500x350)


At the (January) 2002 Tokyo Auto Salon there was a "new" Cosmo! Styled to look like the original Cosmo on this page, it is in fact an MX5(Miata) with a body kit plus an RX8 engine - I understand that it was built by "Mazda Sangyo" which seems to be a subsiduary company that does engineering work, ambulance conversions etc.
I suspect that the "21" means 21st century, because it isn't the 21st anniversary of the original Cosmo. (But, I don't know exactly why they picked 21). The exterior styling has definite Cosmo cues, but the original definitely looks leaner. The interior is nothing like it except the fabric on the seats.

Rumour has it that the Cosmo 21 is going on sale in Japan (hmmm.. it looks too over the top to be anything but a show car, but there have been a lot stranger Japanese cars than this in the past), great news if it does as there might be hope for a rotary MX5. At the show there was also a new Coupe version of the MX5 with a non-removable roof - a rotary MX5 coupe would be close to the original RX7 in concept.
With a greater push for common car platforms the next generation RX7, RX8 and MX5 are rumoured to be the same basic car.


Specs from Japanese press release
Item Spec My comment
Engine RENESIS 13B 654cc x 2rotor i.e. the new generation 13B for the engine for the RX8
184kW (250PS) at 8,500rpm
220Nm (22.4kg-m) at 7,500rpm
Gearbox 5 speed Probably RX7 based (RX8 is 6 speed)
Wheels 17x7JJ  
Tyres 215/40 ZR 17  

The specs in Japanese alse eluded to ABS and the like. I can't read Japanese, there were other items but they are probably of little consequence.
The car is undoubtebly longer, wider and shorter than the original and probably weighs more too. But with that sweet engine this car should be a real hoot to drive.

More Information:

For those wanting to see a Cosmo, I have confirmed (March 2001) that there is one on display at:
Max Kirwan Mazda, 120 Bell St, Preston, Victoria, Australia.
Ph +613 9480 3555 Fax +613 9484 7591
The car was imported to Australia by a Japanese diplomat and was purchased from the diplomat in about 1981.  It is in excellent condition and wears the Victorian registration plates "Mazda". It was about the only thing of interest on the Mazda stand at the 1999 Melbourne motor show.
I'm hoping to get some photos of this car for my page.

Further reading and acknowledgements:
* Special thanks to Mr Nishizawa in Japan for sending me the Sales Brochure/postcard.
* The first edition of 'RX7' by J. Yamaguchi
* An old book from the 70s I saw in the library many years ago, which I photocopied the Cosmo pages from.
* Japanese magazine "CAR GRAPHIC" (most of the L10B photos), August 1996.
* Thanks to Werner Cassel for the scans of the L10A from the German Magazine.
* Fast Fours and Rotaries Magazine, Volume 9 Number 2 (1995)
* Japanese website for Cosmo 21 pictures. More can be found at

Other relevant reading at Craig's Rotary Page (Please go via the INDEX page):
* Books (RX7 by J. Yamaguchi and FF&R back-issues)

Other relevant sites on the Internet (Please go via the LINKS page):
* There are a few snippets of Cosmo information around, see links page
* has a copy of the Japanese press release documents.

This page last updated 17/3/2002
Update History:
17/3/2002 - Added Cosmo 21
16/3/2001 - Major revision of text; re-wrote some sections. Added information about Max Kirwan Cosmo. 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 - Minor content update (Spelling mistakes, tidy up). Background image changed to PG00_02B.JPG
26/4/1999 - Previous known update (May have been some before this)

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