Hi all. In the u.k. The rx8 is taxed as a 2.6ltr engine. However I read that it is a 1.3? Is this because we have two rotors at 1.3 this making 2.6? If this is the case then does a 2.0 Subaru only have 0.5ltrs per cylinder???

Many thanks

 

It's a 1300cc engine but because it works similar to a 2 stroke and there is no exhaust stoke, it is considered equivalent to at 2.6L 4 stroke engine.

 

IMO it is BS to classify the 8 as 2.6l. Just because the rotary does it different does not mean the measurement of the motor changes.

 

If it got the fuel economy of a 1.3L 4 stoke i would agree with you

 

From what I remember it had to do something with the race classes in FIA because the engine has such a small displacement it can race with other cars in that class and therefore smoke those cars so they came up with the idea to multiply the size of the engine by how many rotors and that will even out the playing field. i remember it was something along those lines.

 

it has a displacement equal to a 2.6L 4 stroke engine because it displace air twice as fast as a same displacement 4 stroke engine.

 

Hang on, folks. The rotary is a 4-stroke engine.

The argument for the 2.6 equivalent displacement is that the flywheel on a reciprocating engine has to rotate twice for all of its cylinders to complete their combustion cycle. Therefore, some folks argue that the rotary would need to be measured by rotating twice as well, for comparison.

 

In Japan, the 13b is taxed as a 2Liter engine,

The 13b's true displacement however is 3.9L

Why may you ask?

Each FACE of a rotor displaces 654cc

654cc x 6Faces = 3924cc

 

But there's only one combustion cycle (per rotor) per rotation of the eccentric shaft. So for any given eccentric rotation, only one face is producing power.

 

UK registered rotaries were classified as 2.6 litre engines due to a Vehicle Excise Duty, known as Road Tax, law that was in place for about 4 years from 1999 to 2003 whereby engines of less than 1.6 litres paid lower duty than larger engined cars. It was an incentive for people to run more fuel efficient, less emitting motors. A wankel engined car may be many things but fuel efficient and emission friendly it is not. So they used the argument that a piston engine takes 2 crank rotations to displace its cylinders they applied the same to the rotary and thus it didn't circumvent the taxation rules.

It's academic for taxation in the UK now since all cars built since 2003's Road Tax is calculated on the basis of the CO2 emissions calculated when the car is Type Approved. Even the JDM cars imported to the UK get stung for higher tax and they get registered as 1308cc.

 

So it still comes down to one power stroke per rotor per output shaft revolution, versus one power stroke per cylinder for every other revolution of a piston engine.

Kind of scary that tax collectors are technically savvy enough to latch onto that in order to maximize their take.

Ken

 

It's actually a 1.308 liter.

 

It's a shame that all those piston engines are the ones setting the base line when they have to spin twice as much to make the same amount of work. Inefficient really. Not sure why anyone thought of that.






And off topic posts deleted.

 

In Canada, our emissions and insurance also use that 2x equation.
It's stupid if you ask me.

 

they don't have to be technically savvy, they just gotta hire someone who does, then find whatever they can tax on.

 

I think it comes down to Watt being a better salesman than Hero.

Ken

 

Question then, would you buy the 1.3 or 2.6 ??

 

Wtf

 

That was a joke, right ?

 

a 4 stroke piston engine needs two revolutions of the output shaft to have a power stroke on all of the cylinders, because they are lazy.

the Mazda rotary, however is geared 3:1, so to have a power stroke on all three faces of each rotor, you need three revolutions of the output shaft. in this case you are correct, 6 faces x 654cc per face = 3924cc.

however if we use the same amount of output shaft revolutions as a piston engine uses, two, the rotary has two power strokes per rotor, in a 13B, this is 654cc chamber times 4 = 2616cc.

if we use one rotation of the output shaft, then a rotary has one power stroke per rotor, in a 13B that is 654cc x 2 = 1308cc

this is a case actually where the piston engine is dumb, and we have to make up for its inadequacies. in racing it makes sense to just use the same 2 rotations to get displacement as a piston engine, its the most apples to apples.

this 3:1 gearing also gives the rotary 270 degree cycles, instead of 180 degree cycles, so the strokes are longer.

so the genius of the rotary is that it has longer strokes than a piston engine, AND achieves the same amount of power strokes in half the crankshaft rotations, AND its less complex.


agreed, piston engines are a dumb idea, 3x as many parts, and its all rube goldberg inside...

 

The Wankel may be more space efficient, but it is not more thermal efficient. Going places is what matters most to the average driver, and gas mileage combined with enough power to move the car is the best way to move around. Nobody is going to buy a Wankel because they can go twice as far for the same/lower price with a 1.6 I4. Too much gas is wasted in a rotary (see racecar-ish flames from stock rotaries using straight midpipes). It just doesn't burn hydrocarbons very well.

We all love motors that spin but the general populace never will because this motor is not for them.

 

I just found a few books from my childhood that I'm taking to the Library to donate. Found the 1973 How Things Work and the section on the "rotary piston". I must have realized that an RX was in my future. Features here is a 1972 wagon that would have been in the market at time of printing.