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13B Engine Specs

by David Marsh

The 13B designation refers to a rotary engine made by Mazda. The rotary engine differs radically from the familiar piston engine. Instead of heavy pieces of metal which travel at high speed in one direction, stop, and move in the opposite direction causing vibration and stress, the rotary engine uses parts which travel smoothly around in a circle with little vibration or metal fatigue.

Rotary Basics

Both the piston engine and the rotary engine have a space in which a fuel/air mixture is inhaled, compressed and set afire, and exhaled. The piston engine does it by moving the piston up and down within the same space; drawing in the fuel/air mixture, compressing and igniting it then pushing the exhaust gases out. The rotary engine turns from space to space within a circular housing, carrying the fuel/air mixture along with it, compressing and igniting it and getting rid of the exhaust gases. The circular housing bulges where the triangle draws in the fuel/air mixture and crowds close to the triangle to compress the fuel/air mixture and ignite it, then bulges again in the space where the exhaust gases leave the engine. The triangle has small bars sitting on springs at each corner to seal the fuel/air mixture inside as it turns. Piston engines get energy from the exploding fuel when the shock wave from the explosion pushes the piston down. Rotary engines have a long furrow along the side of the triangle that starts shallow then gradually goes deeper at the other end. It's like a ditch that starts shallow at one end and gets deeper until it ends abruptly with a vertical wall. When the fuel explodes, the shock wave expands against the vertical wall, moving the triangle further around in the circle. The same cycle occurs on all three sides of the triangle.

Comparing Rotary and Piston Engines

Because the rotary engine doesn't use combustion chamber displacement in the same way as the piston engine, the two can't be compared using just cubic centimeters of displacement. The fuel/air mixture in each combustion chamber releases the same energy, making the power output comparable. In rough terms, rotary engine displacement must be multiplied by 1.5 to get a general idea of the size of a comparable piston engine. The power curve, the horsepower and torque delivered by the engine as engine speed increases, can be compared directly. The smoothness of the rotary engine gives it a genuine advantage by extending the power curve. It can spin to a higher speed than the reciprocating piston engine. Both engines come into usable power at about the same engine speed, but the piston engine must be limited or it will shake itself to death. For passenger car piston engines, this is usually between 4,000 rpm and 6,000 rpm. Very few piston engines go faster. Rotary engines as they come from the factory go to 9,000 rpm. The power is readily available and constant as the engine speed increases.

13B Engine Basics

The 13B engine displaces 1,308 cc, uses a compression ratio of 10.0 to 1 and delivers 232 horsepower at 8,500 rpm and 159 ft-lb of torque at 5,500 rpm. In 2002, Mazda offered a turbocharged version of the 13B called the 13B-REW which produced 280 horsepower. The fuel is delivered by multi-port fuel injection and must be premium unleaded --- 91 octane. The rotor housing is made of aluminum with a chrome-steel liner. Mazda makes the side housings from cast iron.

About the Author

In 1990 David Marsh began writing a column in the "Idaho Falls Post-Register" titled "Good Things," which presented restaurant reviews, sports analysis and movie criticism. Besides newspaper columns, Marsh researched police procedures for the Federal government. He has a Bachelor of Arts in administration and a Bachelor of Science in journalism from the University of Utah.

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