Smity42

Do you think she realises that 33 won't get all the way around the world without a fuel stop?

Haha, good form John! P.S. Get a wheel alignment, you know you love them just as much as I do

I lol'd

needs more camber too

Agreed! An excellent discussion. Hopefully there is more understanding out there now

Yes, I can see both arguments clearly, which is why i said it is debatable. I was sold on it being when the original face of the rotor gets back to its original position (ie 3.9L), but now I am fence-sitting. It could be either... But as we have been saying, it doesnt matter how exactly you rate it as long as you understand how that particular method of rating it relates to the equivalent piston capacities

The only way you could fairly do that is if you do it off the crank cycle. But again, this doesn't even work between 2 and 4 stroke. So if you do it on the cycle of the 'combustion medium', whats the cycle of a rotor? One movement or Three? Its debatable... and one way you get 1.3L and the other you get 3.9L Maybe we should average the two and call it a 2.6L

Good point, and if you want to go down sydneykid's path of calling it a 'stroke' motor, which i still disagree with as stroke is a piston movement, you could then say: its a 1.3L 2 stroke or a 2.6L 4 stroke or a 3.9L 6 stroke I'd prefer to see the word 'movement' or yeah 'power pulse' instead of 'stroke' however

True. But when you look at a motor as having more than one piston, half will have pumped air in and half out so it works out pretty much the same. See my post above. Once again, it all comes down to what does capacity mean? Yes we are repeating ourselves here, and really, call it 1.3L or 3.9L, it doesnt really matter as long as you know how to relate that to how piston motors are rated you can make valid comparisons and assesments

And therein lies the problem. I can find NO definition of capacity that doesn't relate to: piston bore * stroke * number of pistons. This obviously does not work for rotarys. People have differing opinions of what capacity actually means when you take pistons out of the equation. Depending on how you define it, you could get 1.3L, 3,9L, or even 2.6L if you try hard enough.

The definition of capicity seems to be a little ambigous, especial when dealing with something not piston based. But call it what you like, the equations to relate it to its piston brothers are the same. It compares to a 1.3L 2 stroke or a 2.6L 4 stroke

he's just giving him sh1t

lol i get it

+1. A lot of what Tas says on the forums could make him look like a tool, but then so could a lot of the stuff most of us says. Its very easy to misinterpret over the net. The reality is that Tas is a top bloke, and you can take your unwarranted abuse elsewhere. Ya sister loves it moist Ditto! I'll be happy with a back seat run... Me too! Good form. Mountain run? Nothing faggy about tig old bitties

Yes, we CALL it a 2L but when we COMPARE it to a 2-stroke we DO halve it and say it is the equivalent of a 1L 2 stroke. in the same way we can CALL a 13B a 3.9L, but when we COMPARE it to a 4 stroke we multiply by 2/3 (2.6L), or when we COMPARE it to a 2 stroke we multiply by 1/3 (1.3L). The opposite argument would be to CALL a 13B a 1.3L and when we COMPARE it to a 4 stroke we multiply by 2, or when we COMPARE it to a 2 stroke we do nothing. However I agree with you that it should be called a 3.9L. The actual measurement of capacity is a little inconsistant even between 2 and 4 strokes. But what is relevant is having a way to compare them, and we do this using relative timescale, to acheive the ratios above. Going back to the pump analogy someone used a while ago (it might even have been you sydneykid), if I wanted to compare two pumps what would i look at? First i would look at how much each pumped with one revolution of the input shaft. Its not fair to spin one twice and one once. Then i would look at what is the maximum speed i can spin each one (rpm). If they both pump the same amount in one turn of the shaft, but one is capabable of spinning twice as fast, it has the potential to pump more. Then you would get into how much energy is required to turn the shaft of each one (this is where you get into efficiency, etc). You could then start to look at the physical size of the pumps, etc. I guess this is a 'black box' approach, where the internal workings of the pump are irrelevant, if we want to compare them we need to look at how they acheive what they are designed to do. So going back to our engines with this logic (black box approach): Lets take a 13B, a random 2.6L 4 stroke, and a random 1.3L 2 stroke. Lets pretend we don't know how these work, we just want to compare them. What is an engine designed to do? turn an output shaft. If we turn the output shaft once, the 13B will have pumped 1.3L of air, so will the 2 stroke, so will the 4 stroke. So they are roughly the equivalent capacity, even though they are labelled differently. Next, you would compare the max RPM of that output shaft. For the 13B this IS 9000 RPM. For the piston engines, it would depend but on average it would be a little less than that. What the internals of the engine are doing here doesn't matter remember, black box approach. The output shaft is what we are comparing. Now to compare the engines, you would have to look at the power/torque graph over the whole RPM scale, as well as fuel economies, size and weight of the engine, etc. But you have a fair comparison to do this as the capacities are EQUIVALENT. So, what if we were to put a 1:3 ratio on the output of the 4 stroke piston engine? Suddenly, its only pumping 1/3 as much air with each rotation of the crankshaft, but is capabable of spinning 3 times as fast. So you would have to take that into account when comparing to other engines, it's power curve would be the same, but spread over 18000 rpm instead of 6000 (say). It would make less torque, but spin faster. Gear ratios do not give an engine an outright advantage, they just change the rpm range it operates in. Likewise if we imagine for a second a wankel that doesnt have this inherit 1:3 ratio. Suddenly when I turn the output shaft once, its going to have pumped a full 3.9L of air. Nice. BUT, its now only capable of doing 3000 rpm, so I have to take this into account when comparing it to another engine. Basically I guess what I am saying is the workings of the engines are so different between piston and rotary engines, the only way we can compare them is with this 'black box' method. The engines still do the same job, that is to turn the output shaft, so we compare how they do this. If one has an internal gear ratio it does not matter, it will give it an equivalent capacity advantage but limit its RPM, or vice versa.

Deja Vu anyone?

well said!

Yeah i actually stuffed it up in my V12 vs 6 comparison - it would still only be half the measured capacity that has fired. The rest is still relevant but - see edited version

But wait! Rotary engines ARE a 2 stroke: Sorry, Couldn't help myself . Yes i did notice that you clarified with '2 stroke piston engine' everywhere. However, by definition a 2 stroke is a piston engine, but thats an argument you are not going to come round to, so I am not going to bother arguing it again. I am however still waiting for a definition of a 2 stroke you can point me to that you can make a rotary fit in to. Edit: I just realised why i balls'd up that comparison. I still disagree though: What you actually need to look at is crank rotations. For a 4 stroke - one complete combustion cycle of a piston rotates the crank 720 degrees For a 2 stroke - one complete combustion cycle of a piston rotates the crank 360 degrees So if we rotate the crank the same amount, the 2 stroke fires twice as much, so we double its capacity comparing it to a 4 stroke. For a Wankel - one complete combustion cycle of a rotor rotates the eccentric 1080 degrees, so to compare it to a 4 stroke we multiply by 720/1080 or 2/3. I suppose sydneykid is going to comeback now with his 3:1 ratio argument. I don't have an answer for that other than to agree to disagree. The only other argument you could put forward for doubling a 2 stroke capacity is because when we normally measure capacity we only count one half of the combustion process (the 'top' half of the piston), so we need to double it to count the other half (the 'bottom' of the piston). but this also does not apply to a rotary as we have already counted all 3 faces in obtaining our 3.9L figure.

Yeah bro, schmick as. I love a good alignment Old mate with the tats did it. He remembered it from last time he did it and set it up the same

yay car is at quickfit for wheel alignment . Had to deal with some nub but who couldn't seem to cope with the fact i yas giving him a sheet of the required settings. Both the dudes who know how to align appear to be working though, they should work it out

And once again you are back to doubling the capacity 'because it's a 2 stroke'. Forgetting for a moment that it ISN'T a 2 stroke, can you tell me what the basis is for doubling a 2 stroke's capacity when comparing it to a 4 stroke? Don't just say we double it 'because it's a 2 stroke', but tell me what the reason is that we double a 2 strokes capacity. Then ask yourself, "does the same apply to a rotory?". You will find that it does not.

Wishful thinking maybe... do they make one for 31s?

Probably because thats not what they are... Probably because thats not what they are... You mean we shouldn't ignore their 3.9L capacity, WANKEL cycle, and low(ish) compression ratio, don't you?