ROTARY HISTORY 6
This column is Copyright 1997-2001 by Edwin Krampitz, Jr., unless indicated otherwise. Please ask for permission to reproduce.
*Reprinted on http://rotarywiki.com with consent of the author.
- Part 1:The Smallest Wankel Of Them All
- Part 2: The Smallest Production Aviation Wankel
- Part 3: Biggest of Them All
- Part 4: The Citroen Connection
- Part 5: Russian Rotaries
- Part 6: The Orphan Mazdas
- Part 7: The One that Won in '91
- Part 8: Chinese Experiments
ROTARY HISTORY 6: THE ORPHAN MAZDAS
Most of you are familiar with the Mazda family of rotaries that includes the 2-rotor 12A and 13B, the 3-rotor 20B and 13G, and the 4-rotor R26B. The numerical part refers to the engine size in deciliters, excepting the 13G. All have a rotor radius (R, or actually R-prime) of 105 mm and an eccentricity (e) of 15 mm. The 12A has a rotor width (B) of 70 mm; B for these other engines is 80 mm. The 12A, 13B, and 20B have all seen extensive production for street vehicles and other applications, and the 13G and R26B were variants for racing. Of course, the R26B powered Mazda's 1991 Le Mans winner. But Mazda went into production with other, forgotten rotaries.
One was the L10A and 10A, the first variants of the 12A/13B family. R-prime and e were the same; B was 60 mm, giving a displacement of 491 cc per rotor or 982 cc (59.9 ci) for the 2-rotor engine. The L10A was used in Mazda's first production rotary car, the rare L10A/L10B Cosmo Sports of 1967-1972. A very few were exported as the 110S, after the original power rating of 110 hp at 7000 rpm. Only 343 of the original L10A Cosmo were built before the extensively revised L10B came out in 1968. With different port timing and carburetion, the 10A engine (the "L" was dropped) now put out 128 hp at 7000 rpm. When production ended, 1,176 L10B Cosmos had been built. In contrast to later Mazda practice, these 10A engines had aluminum side and intermediate housings and triple oil seals. These housings' rubbing surfaces were hot-sprayed with layers of carbon steel.
The 10A was detuned and revised for the other cars it was used in: the Familia/R-100 and Japanese and European versions of the Savanna/RX-3. The R-100 was sold here in 1970-1972 with the 10A, but the US RX-3 always had the 12A. This 10A typically put out 105 hp at 7000 rpm. It remained available elsewhere until about the beginning of 1974: using the 2x factor for equivalent displacement as European authorities did for taxes kept it in the under 2-liter class. The 10A established the normal Mazda practice of cast-iron side and intermediate housings and double oil seals. Unfortunately, the parts unique to the 10A have been unavailable for years, and most in surviving Mazdas have been replaced with 12As. Supplies started drying up as soon as the early '80s. But several years ago Mazda cast a replacement 10A rotor housing at a huge loss for an Australian restoring a Cosmo Sports. I doubt Ford would let Mazda do this now!
The 2-rotor 13A was rare even when new. It had completely different rotor dimensions: R' x e x B = 120 x 17.5 x 60 mm, for an engine displacement of 1309 cc (79.9 ci). It produced 126 hp at 6000 rpm and 127 lb-ft of torque and had a 9.1:1 compression ratio and a 6500-rpm redline. The 13A was used in one car: the 1970-1972 R130 Luce rotary coupe, never exported here. It was styled by Bertone and related to the rear-drive piston-powered Mazda 1500/1800 sedans. This was the only production front-drive rotary Mazda, though only 976 were made, and the 13A was designed just for this application to give relatively more low-speed torque. The R130 was capable of 118 mph. The 13A was never developed further or offered in any other vehicle, but the Aussie Cosmo restorer--who also restored an R130--found that some parts were still available from Japan!
Mazda made many experimental and developmental rotaries, and the 20B's status is questionable. Also note that early 12As are almost completely different from late 12As. But the (L)10A and 13A qualify as true orphans.
POSTSCRIPT FOR INTERNET: If you're aware of how Japan taxes cars, you may wonder how Mazda has been able to sell any cars there with the 12A, 13A, or 13B. Taxes shoot up dramatically when displacement exceeds 2 liters. Japanese authorities use a 1.5x factor to tax rotary engine displacement instead of the 2.0 used in Europe and elsewhere. This means that even the 13B still is taxed as an under 2-liter car.
- Mazda in Japan http://www.mazda.co.jp