Backround
Not to be confused with a Radial engine which has the cylinders spinning around the crankshaft and was popular in aircraft up to WW2. The idea for a rotary engine goes back to 1673. In 1759 James Watt built a rotary steam engine. Patents were filed in 1929 by Dr Felix Wankel who named it the 'Grease Turbine', he was plagued by problems for the next 50 years. It has taken Mazda many years to get them where they are today, along the way many other companies tried and abandoned them in favour of simpler and cheaper technology. For the purpose of this article, I will refer only to the popular engines made by Mazda as there are many other rotary engines around the world - did you know that all Lear jets have a small rotary motor which supplies auxhiliary power? To read the full story click here

How do they work?
The motor is a 4 stroke Otto cycle engine in that it has intake/combustion/power/exhaust phases. As you can see in the diagram there are no cams, conrods or valves - which gives it less parts, and in theory makes it more reliable, at any one time there is one chamber busy with combustion, another with induction, and the third is busy exhausting or igniting gas. The plugs fire once per crank rotation (navy), where a piston 4 stroke fires once every 3rd rotatation. The firing order seems strange but if the top plug (trailing) were to fire first it would force the rotor backwards and damage the motor. The motor can and will run on the bottom plug (leading) only.
Most Mazda rotaries have 2 cylinders with the rotors at 45 degrees from each other. There are 3 (13G, 20B) and 4 rotor (R26B) motors available overseas, and even a 6 rotor motor available in England (see pic on free smalls page) All rotary engines have heavy counterweights mounted on each end of the crank for balancing.
The motors will run on petrol, alcohol, hydrogen and even kerosene (jet fuel) with a glowplug fitted.

Spark Plugs
The LeMans winning engines were fitted with 3 plugs per cylinder (late trailing) and I have seen a design of a 6 plug/cylinder motor - the theory being that you can never get enough spark, because there is a high speed wind blowing across the spark plugs. You can also see why rotary spark plugs have recessed electrodes. Normal plugs will damage the rotor apex seals.

2 Stroke Technology?
Many people are under the impression that a rotary works on the same principles as a 2 stroke motor - and they couldn't be more wrong. A 2 stroke uses it's exhaust to draw in the following intake charge and must close the intake port completely to prevent the intake charge from blowing backwards through the carb and so also boost the compression ratio, it must also have a tuned expansion chamber to reflect pressure into the cylinder at precisely the right moment. A rotary has no such problem as the cycles are seperated. A rotary uses exhaust gas suction to draw in the following intake charge and any exhaust back pressure will reduce intake velocity, which is fine - if you want an economical motor. The only thing the two motors have in common is that oil must be added to the intake mixture to lubricate the cylinder walls and this is probably where the misunderstanding originated. In fact, when Norton used rotaries against the 500cc 2 strokes - they were restricted to 380cc and one of them still holds the lap record at the Isle of Man TT circuit.

Methanol
Many drivers mistakenly run the motors on methanol thinking that it will reduce internal temperatures, but forget that methanol contaminates engine oil very quickly and damages bearings if the oil is not changed after every meeting. Also you need to keep the motor rich at all times or internal temperatures skyrocket. Mineral oils such as 2 stroke oil do not mix well with methanol which is another drawback as the motors must have oil added to the intake mixture.

Tuning
Many top tuners use exhaust manifold temperature to tune the motors because it is difficult to read rotary spark plugs correctly. A temperature of around 900 deg/C is considered optimal, less and the motor is rich, more and the motor is lean. They also use oil temperature to determine if the motor is overworking, esp in turbo motors with 140 deg/C being the alarm zone.
For more info click here

Why are they so loud?
As I explained earlier the less exhaust back pressure the better, so most race cars are fitted with a megaphone type exhaust. Also - standard engines come with a baffle plate in the exhaust port which is one of the first things racers chuck away because it restricts the exhaust port. Also the exhaust port can be widened and lengthened considerably to promote evacuation of exhaust gas and induction velocity. There are no valves to block sound waves and with a bigger port, sound travells straight down the unrestricted exhaust pipe.

Why all those flames?
Mazda rotaries run hotter than normal motors with exhaust temperatures around 1000 deg/C and oil temperatures of around 120 deg/C. They are usually run as rich as possible to cool them, when a driver brakes, exhaust temperatures rise as the motor 'leans out' and any unburned fuel and oil is ignited. A rotary motor must have oil mixed with the fuel to lubricate the cylinder walls - just like a 2 stroke and often you can see blobs of burning oil flying from the exhaust - esp as the motor is blipped after a race. A car showing a permanent flame is either way too lean or has damaged it's seals.

Why do the drivers rev them so hard, even when standing?
No - they are not being windgat, the spark plugs foul very easily because race engines run with much more 2 stroke in the mixture to prevent seizing. Genuine Mazda race plugs sell for around R100-00 each - so if you thought your plugs were expensive - think again! The answer is to run less oil in the mixture but risk rotor seizure, most drivers would rather buy plugs and rev the motor to keep them alive.

How much power do they make?
A lot less than you think - The following are rough estimations of what the various motors should be capable of at sea level:
10A - 100 bhp (std)
12A - 125 bhp (std)
12A turbo - 160 bhp (std)
13B - 135 bhp (std)
13B turbo - 182 bhp (std)
13B 2 turbo - 210 bhp (std)
13B Street/Bridge Port - 200 bhp max
13B Peripheral Port - 280 bhp max

How high do they rev?
1300cc (13B) Mazda rotaries tend to break their crankshafts between the two rotors at around 11 000 RPM, depending on the age of the crankshaft and how well the motor has been balanced.
1200cc (12A) Mazda rotaries tend to break a little higher because their rotors and counterweights are lighter.
Many overseas racers spend a lot of time and money lightening their rotors as much as possible, I believe that Titanium rotors are available but cost their weight in gold. The optimal rev range is usually between 5 - 9000 rpm, unusually the motors make maximum torque very low down (around 3000 rpm) and the torque curve remains more or less flat from there on.

What engines are available?
Click here for a list of all rotary motors.
In South Africa, only the 10A (1000cc), 12A (1200cc) were freely available. All 13B (1300cc) motors are aftermarket imports and spares must be specially ordered. Needless to say it is very difficult to source the right parts and with our exchange rate - sometimes not worthwhile.

Should they be banned?
Ten years ago the top hotrods were fitted with 1600cc pushrod engines modified by companies overseas like Mass. It was easy to build a rotary and make more power. Todays 2L 16v engines are easily capable of 280hp and more, and still remain reliable.
The Mazda rotary is probably the hardest engine to cheat with in the world. The only internal difference between the motors is the width of the rotors, the length of the crankshaft, bearings and counterweights. Porting is highly restrictive in that one cannot go too far or face seal failure.
It is almost impossible to bore or stroke a rotary - the shape of the rotor (trochoid) and epitrochoid (housing) see to that.
Let them run in a class of their own and you will have competitive and exciting racing - ie: The popular Formula Atlantic series run here a few years ago used 12A motors.
Let them run in the midgets and V8 Saloons with turbos - yes.
Ban them - what for?

To read more about rotaries in racing click here