The displacement thing...

This is all complex as the accpeted way of measuring the displacement of a piston engine is by looking at the volume of all cylinders. I.e. 4 cylinders of 250cc each = 2 litres, or 8 cylinders of 712.5cc = 5.7L.

So Mazda say there are 2 combustion chambers of 654cc each = 1.3L displacement. The difference is in how often the 654cc of mixture is inhaled, and burned to make power.

Think about a single cylinder (reciprocatin) 4 stroke engine of 654cc. The "displacement" of 654cc of air/fuel mixture produce one "bang" or power pulse for every 2 revolutions of the output shaft.

Compare this to a SINGLE ROTOR rotary engine with a chamber volume of 654cc, and look at the attached animation.

The rotor turns at 1/3rd the speed of the output shaft. Each time the output shaft has turned 1 full revolution, there has been one power pulse from a 654cc volume of air/fuel mixture.

Therefore, the rotary engine produces twice as many "bangs" per engine revolution as an equivalent capacity 4 stroke. Or think of it this way - for 2 revolutions of the output shaft of the single rotor - we get the "effectiveness" of 1308 cc of air/fuel, compared to 654cc in the piston engine.

(It is a little bit like comparing a 654cc 2-stroke with a 654cc 4-stroke.)

So - we take our single rotor 654cc, and put another rotor on it - that makes it into a 13B. For each revolution of the output shaft, we get 2616cc of air/fuel burning.

So a twin rotor rotary of 654cc displacement (per chamber) is "equivalent" to a 4 stroke of 2.6L

Comparing the 2 rotor to a multi-cylinder piston engine... Our 2 rotor gives 2 power pulses per revolution. With a 4-stroke piston engine you get one power stroke per 2 revolutions per cylinder. So to achieve the same number of power pulses/revolution as the rotary, the piston engine needs to have 4 cylinders ( = 4 power pulses for 2 revolutions, which is equivalent to 2 power pulses / revolution).

A 2.6L four is a bit "big" to have a nice reving engine though, (due to the large pistons/reciprocating masses)

The other thing that makes it a little more complex, is that the tourqe fluctuations in the rotary produce power for more degress of crankshaft revolution than in a piston engine. So the torque fluctuation (smoothness) is more comparable to a 6 cylinder 4-stroke piston engine.

There you go. I write software, and now I think I can explain things as well :p

insert :teacher: smilie here

Cheers,
Hymee.

 

And Kas,

Great news, whatever it is...

I would have been happy for a free new engine (or a free condensor in my case).

Cheers,
Hymee.