what's the point of fast cars?

I can sort of see the French way of looking at it but the USA's one is just stupid "It's got 3 sides so it must be a 3.9!" could be something to do with the fact they were thrashing everything over there in racing.

Am I alone in thinking a renesis powered Elise would be a great idea?

Definitely not.

Someone in Germany is building a Renesis powered RX8, and I'd love to stick a rotary into the Sera.

Richard

Don't Mazda already do that?

How did you work out the 1.3 size?

Argh! I mean MX5. *bangs head*

Richard

It has two chambers and a swept volume of 654cc per chamber. I didn't 'work it out' - that's what it is, by specification.

Richard

It's the number of rotors x by the largest volume of the combustion pocket during the cycle.

RichardK waffled thus:

Just out of interest, what does it show as on the logbook?

I believe, 26xx (2612 or something) - the lease company has the logbook.

They're in the highest band for emissions, too.

Richard

It should be 3930cc

No, it should be 1308cc. My insurance and the DVLA rate it as 2616.

Where do you get 3930 from, aside from thin air?

Richard

Lol, I haven't a clue, it should be 654cc x2chambers x2rotors =2616cc

You only have one rotor per chamber ;)

Richard

By chamber I ment the spaces left between the rotor and the walls.

Wankel for legal stuff like tax just like any other positive displacement engine is rated on swept volume PER revolution of the output shaft. This is because when the rules where made on how to rate engines for legal and tax purposes there were only Otto 4 stroke piston engines and the law makers can't be arsed to rate different engines properly.

Using induced charge to size engines, the working volume of all 4 stroke piston engines is actually 1/2 the rated capacity as they only induce a fresh charge of air every other stroke. Ignoring valve timing the compression and power stokes do not move air in and out of the engine. This is how makers of Wankels declare the chamber size - on amount of working air induced not rated displacement. This is the critical volume for working out anything like volumetric efficiency and would be a much more sensible way to rate engine size. It's too big a mind shift for any government to sell to the public, too many people would complain that they had been deprived of engine capacity or the government was stealing some of their engine and would then insist they need engines twice the size to make up for the loss.

For Wankel chamber size, if you want the method using integration of the locus of the tip on the chamber wall at inner and outer dead centre and subtracting the rotor profile to find swept volume you can work your way though this.

Total capacity of each rotor is 3 x 3^0.5 x R' x w x e. R' - nominal rotor tip seal contact point to rotor centre. w - rotor width e - radius of eccentric on output shaft. times number of rotors for multi rotor engines.

Rated size is twice this as it does the full 4 stroke cycle every rev and not half of a cycle. USA it's rated as 3x because they didn't want the poor sad under performing domestic V8 dinosaurs showing up so badly. Or, they found they could decide what the rated size of a Wankel was without messing with current rated size of 4 strokes, so they seized on the opportunity to c*ck it up even more.

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Thanks, that's exactly the answer that I was looking for.

Which is 1308cc. There are three 'sections' on the rotor. The output shaft rotates 3 times per rotation of the rotor. The swept volume of the chamber is 654cc and there are two chambers.

One rotation of the output shaft, 1/3 rotation of the rotor (but, one complete intake/combustion/igntion/exhaust cycle).

And this is presumably why we have the tax and legal ratings of 2616cc for the Renesis.

Richard

[...]

It makes more sense to triple the "swept volume" than double it as whilst each chamber is analogous to one cylinder each rotor is analogous to *three* pistons and there are three firing pulses per rev...

Bit like "not quite the clock speed" processor numbers or citrus apples.

A