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Mazda engines / How Wankel rotaries work / Brief Mazda rotary history

Mazda Engines

Mazda has produced dozens of different prototype engines over the years, and many variants of final production versions.
Here is a chart that will give a quick indication as to the maximum power developed by each engine for the year that it was produced. Since 1997 there have been a number of prototype non-turbo 13B engines, the most recent version in the RX8 making nearly 300hp.
Quick chart of mainstream mazda engines producedNotes:
*Power figures from many different sources, so may be in-accurate
*All engines and years listed here were years that specific engine was available from Mazda

*10A = 491cc x 2 rotors
*12A = 573cc x 2 rotors
*13B = 654cc x 2 rotors
*20B = 654cc x 3 rotors
*R26B = 654cc x 4 rotors

*"T" at end of engine name means turbocharged
*If not turbocharged, all race engines are Peripheral ported
*All race engines fuel injected after about 1982

How Rotaries Work:

How rotarys work (640x480)

The wankel rotary works by the volume of the chamber enclosed between the rotor and the rotor housing changing.
Intake, Compression, Ignition, Expansion, Exhaust all work as for in a piston engine, but as the rotor has three sides it is all happening at the same time.
Despite this, as each rotor gives a power stroke per revolution it is therefore the same as a two stroke. So effectively all of the engine's capacity is being used for every rotation of the output shaft (as for a two stroke). Therefore the actual volume used is twice that of a 4 stroke.

ie a 1.3 liter 13B engine is 'equivalent' to a 2.6 liter 4 cylinder 4 stroke in terms of power pulses and the capacity of the engine used.

Motorsport bodies however apply a 'correction factor' to the rotary's volume anywhere from 1.8 to 3.0

Rotarys make high power for their size because of their volumetric efficiency, which is a measure of the volume of air going into the engine divided by the capacity of the engine. (for example a 1.0 liter engine at 100% volumetric efficiency intakes 1.0 liters of air per revolution). Obviously, more air going in means more fuel and thus more power.
Most stock piston engines only have a VE of 50-60%. A stock rotary is about 70%. Peripheral ported rotarys can go over 100% (which means that it is more air than the engine's volume). This phenomemon does not occur in normally aspirated piston engines (except in highly modified race engines). It does occur in turbocharged engines fairly often though.

On the other hand, rotaries use more fuel than a piston engine of the same size. This is due to their poor "thermal efficiency" (which means that more of the fuel is used to heat up the engine than the working gasses within it). This poor thermal efficiency is because of the very long and thin combustion chamber (more surface area thatn the same capacity piston engine).

All production rotarys made by Mazda use two spark plugs per rotor to ensure that as much of the mixture is ignited as possible. In reality the power output of the extra plug is marginal (5% perhaps), however it is mainly used to lower the emmissions from the engine.
However, the Le Man's R26B engine has a third "late trailing" spark plug even higher up the combustion chamber. This, combined with a variable length intake manifold and peripheral porting gives 700 JIS PS from what is effectively two normally aspirated 13B engines (350HP from a non turbo 13B is quite impressive).

A brief history of Mazda Rotarys

Return-Path: ^^x22mrmazda (Felix Miata) ^^ Date: Fri, 24 Oct 1997 20:37:30 -0400 Reply-To: mrmazda@gate.netT Organization: Quite Short of Ideal To: Craig Pugsley <> Subject: More History

>From another old Mazda publication I forgot I had "The Mazda Rotary Engine: A Ten-Year Revolution" (Jan '78):
6107 Rotary engine license agreement with Audi NSU/Wankel validated by Japanese Government and rotary engine development began.
6111 First prototype rotary engine with one rotor completed.
6204 Prototype rotary engine with two rotors completed.
6405 Prototype rotary engine with four rotors completed.
6503 Research on rotary engine's exhaust emissions began.
6703 Thermal reactor development began.
6705 Cosmo Sports (Mazda 110S) introduced.
6712 Development of rotary engine with direct fuel injection system began.
6801 Mazda received Motor Trend Magazine Award for production application of rotary engine.
6807 Familia Rotary (Mazda R-100) introduced.
6808 Cosmo Sports (Mazda 110S) won 4th place in 'Le Marathon de la Route 1968, 84 hour endurance race.
6910 Luce Rotary Coupe (Mazda R-130) introduced. Mazda R-100 with a thermal reactor approved in the exhaust emission certification test by the US department of HEW.
7005 Capella Rotary (Mazda RX-2) introduced.
7006 Export of rotary engine cars to the US market began (Mazda R-100).
7109 Savanna (Mazda RX-3) introduced.
7110 Devolopment of fuel injection rotary engine with pre-chamber began as an emission reduction concept.
7201 Mazda RX-2 received 1972 Car of the Year Award from Motor Fan Magazine of Japan. Mazda RX-2 received 1972 Import Car of the Year Award from Road Test Magazine of the USA.
7210 Luce (Mazda RX-4) introduced. Development of stratified charge rotary engine with fuel injection system began as a NOx reduction concept.
7301 Mazda RX-3 Rotary Wagon received 1973 Import Car of the Year Award from Road Test Magazine of the USA.
7302 Mazda RX-3 & RX-4 met the 1975 Statutory Emission Standards in the tests carried out at the EPA.
7303 Mazda testified at the EPA Hearing for the 1975 Statutory Emission Standards.
7311 Switchover to the redesigned new series of rotary engines.
7312 Luce (Mazda RX-4) mounting 13B engine added.
7403 Mazda testified at the Committee on Motor Vehicle Emissions of the National Academy of Science that the significant improvement in fuel economy was possible in Mazda 1976 models.
7404 Mazda Rotary Pickup introduced in the US market.
7407 Parkway Rotary 26 introduced.
7411 Models with improved fuel economy for Japanese market went on sale.
7503 Roadpacer introduced.
7510 Cosmo (Mazda Cosmo or RX-5) introduced. Models with improved fuel economy for Japanese market went on sale.
7511 Models with improved fuel economy for the US market went on sale.
7601 Mazda Cosmo AP received 1975 Car of the Year Award from Motor Fan Magazine of Japan.
7606 Mazda awarded a letter of commendation by the Japanese Environment Agency for its outstanding efforts in emission control.
7607 Rotary engine license agreement with Audi NSU/Wankel revised.
7707 Cosmo L introduced.
7710 Luce introduced

This page last updated 16/1/97

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