Why Do Rotaries Suck?

[bozodos]

hahaha good call scathing

[Birds]

Pfft I did the quarter at Calder in my Roadpacer with a caravan in tow. Had to have wheelie bars on the back of that just to stop the whole thing entering flight. Not to mention all the mortar bags we lined the engine bay with.

[GT-R32]

  Birds said:

Pfft I did the quarter at Calder in my Roadpacer with a caravan in tow. Had to have wheelie bars on the back of that just to stop the whole thing entering flight. Not to mention all the mortar bags we lined the engine bay with.

You would have had plenty of room for the mortar bags, given the dimensionally small size* of the 13B, in an engine bay fit for a V8.

*Nothing to do with displacement.

[Birds]

Yup, now that's what I call efficiency

[scathing]

  Birds said:

Pfft I did the quarter at Calder in my Roadpacer with a caravan in tow.

You should have just converted a Parkway into a motor home.

[JayTay]

Wow, epic thread, just got through the whole thing. Tech info is awesome, it should be cleaned and stickied.

On a side note I'm stoked to find out that because my rb25 is only going through the ignition phase of combustion two cylinders at a time, I can tell everyone a drive a .833 Litre motor.

Makes a rotary look kinda p!ssweak doesn't it?

From what i gather from reading so much of the excellent information and working out my own opinion, classes should work like this.

13b twin rotor (with 6 combustion faces in total) has an effective capacity of 3.9 litres. The same way a 6 cylinder piston motor (2 or 4 stroke) with an individual cylinder displacement of 654cc would displace 3.9 litres total.

I can't believe that is even up for debate.

Give the thing a 20% bonus for rubbish efficiency and the figure is still above 3 litres.

Rotaries are popular for motor racing as they have a massive class advantage.

Saying this, if you don't get at least a half wood when you hear a triple or quad rotor on song (peaking at a glorious 3,000 to 3,666.67) RPM, you probably don't have a heart.

[Birds]

Credit to you for making it through the whole thread before replying...

You can tell people your rb is a .833 litre motor if you're certain the other 4 cylinders don't have combustion occur inside them at any point. The reason capacity was up for debate is because, unlike you, not everyone here believes the rotary has 6 combustion chambers. Given combustion occurs in the same chamber for each rotor housing, some of us feel it legitimate to say the twin rotary has effectively 2 cylinders...ala as if your rb was to run on 2 cylinders. Combustion faces are irrelevant, for flipping the face of a piston in the piston engine every combustion wouldn't change the engine capacity; it would still combust the same number of times. The rotary just gets through the Otto cycle quicker, just like a 2 stroke is quicker than a 4 stroke.

Problem is, you like so many are still trying to think of rotary capacity in terms of piston engine capacity when they are quite different in the way they are measured and applied. Just as a 1 litre two stroke piston engine capacity has different meaning and class weighting to a 1 litre four stroke piston engine, different also is that of the rotary and to look at or compare capacity without using equivalence based on power and efficiency is a giant narrow minded moot point.

[GT-R32]

  JayTay said:

Rotaries are popular for motor racing as they have a massive class advantage.

Saying this, if you don't get at least a half wood when you hear a triple or quad rotor on song (peaking at a glorious 3,000 to 3,666.67) RPM, you probably don't have a heart.

You're not measuring the equalising RPM in the same place.

[JayTay]

  Birds said:

Credit to you for making it through the whole thread before replying...

You can tell people your rb is a .833 litre motor if you're certain the other 4 cylinders don't have combustion occur inside them at any point. The reason capacity was up for debate is because, unlike you, not everyone here believes the rotary has 6 combustion chambers. Given combustion occurs in the same chamber for each rotor housing, some of us feel it legitimate to say the twin rotary has effectively 2 cylinders...ala as if your rb was to run on 2 cylinders. Combustion faces are irrelevant, for flipping the face of a piston in the piston engine every combustion wouldn't change the engine capacity; it would still combust the same number of times. The rotary just gets through the Otto cycle quicker, just like a 2 stroke is quicker than a 4 stroke.

Problem is, you like so many are still trying to think of rotary capacity in terms of piston engine capacity when they are quite different in the way they are measured and applied. Just as a 1 litre two stroke piston engine capacity has different meaning and class weighting to a 1 litre four stroke piston engine, different also is that of the rotary and to look at or compare capacity without using equivalence based on power and efficiency is a giant narrow minded moot point.

The same way, that you cannot tell people a rotary has only two combustion chambers when the other faces of a rotor are carrying out combustion processes.

The interesting thing is that you say I, and so many others are using examples of the rotary engine and applying the operating conditions af a piston engine.

I say the problem with this is you are just as guilty of applying piston principles as you claim we are.

Your argument as to the two combustion chambers is based on the idea of a piston engine, whereby a combustion chamber is defined by a specific, unchanging physical location. This is, by your own logic, faulty thinking when applied to a rotary engine.

Any face of a rotor not engaged in the process of ignition is still engaged in a part of the combustion cycle.

Ignition is not combustion. It is a part of the cycle.

The principle is that there are virtual cylinders which can exist in different states at any given time. This is hard to grasp as it somewhat goes against our basic human understanding of physics, that an object can effectively be something else at any one given time.

You are absolutely right about the 1 litre 2 stroke vs a 1 litre 4 stroke. They are not evenly matched, however here you are muddying the argument into racing classes not displacement. On the matter of displacement a 1 litre 4 stroke and a 1 litre 2 stroke have IDENTICAL displacement.

For racing 2 strokes are great, as pollution, noise, oil burning and a lack of life expectancy are not issues for motors that see regular rebuilds.

2 strokes, are not particularly practical as an every day use motor, as these reliablitiy factors would not be tolerated in a street car for the masses.

Now for the above paragraph, substitute the word 2 stroke for rotary and suddenly the comparisons between a rotary and a 2 stroke become far clearer.

A rotary may be somewhat more reliable than a 2 stroke motor, however suffers from an inherently ineffecient design.

Great Thread.

[DRD-00F]

Definately a great thread... I wish people would stop replying in it

My question about the compression test is probably still my favourite bit... if there were truly only 2 combustion chambers, then you would only have to turn the E shaft 360 degrees to do a complete compression test on the engine...

"If you were to do a compression test on a rotary, how many degrees would you turn the E shaft? If it's only got 2 ignition chambers it should only need 360 degrees yeah? That's 1 cycle yeah?? Cause a compression test only requires one cycle of the engine, any more and you're repeating yourself... and we all hate that right? "

but whatever, I'm not arguing this anymore, both views are right, and motorsport plots them at about 2.6 which is fair. I can only imagine the discussion they had about this...

I class them as a 3.9L wankel cycle, nothing more, nothing less...

[bozodos]

oh and they only rev up to 3000rpm due to the 3:1 eccentric shaft

[GT-R32]

  bozodos said:

oh and they only rev up to 3000rpm due to the 3:1 eccentric shaft

Where is RPM measured? Where is BHP measured? Where is torque measured?

You're talking about rotor speed. Not engine revolutions.

[DRD-00F]

He's taking the piss matt, calm down

Birds, stop posting... I see your slanty name down there!

[GT-R32]

  DRD-00F said:

He's taking the piss matt, calm down

Birds, stop posting... I see your slanty name down there!

I'm calm as the Carribean sea (man, I wish I was back there right now).

But I get your point, I think I have been persistent enough in the past in this thread, LOL.

[Birds]

  JayTay said:

The same way, that you cannot tell people a rotary has only two combustion chambers when the other faces of a rotor are carrying out combustion processes.

The interesting thing is that you say I, and so many others are using examples of the rotary engine and applying the operating conditions af a piston engine.

I say the problem with this is you are just as guilty of applying piston principles as you claim we are.

Your argument as to the two combustion chambers is based on the idea of a piston engine, whereby a combustion chamber is defined by a specific, unchanging physical location. This is, by your own logic, faulty thinking when applied to a rotary engine.

Any face of a rotor not engaged in the process of ignition is still engaged in a part of the combustion cycle.

Ignition is not combustion. It is a part of the cycle.

The principle is that there are virtual cylinders which can exist in different states at any given time. This is hard to grasp as it somewhat goes against our basic human understanding of physics, that an object can effectively be something else at any one given time.

You are absolutely right about the 1 litre 2 stroke vs a 1 litre 4 stroke. They are not evenly matched, however here you are muddying the argument into racing classes not displacement. On the matter of displacement a 1 litre 4 stroke and a 1 litre 2 stroke have IDENTICAL displacement.

For racing 2 strokes are great, as pollution, noise, oil burning and a lack of life expectancy are not issues for motors that see regular rebuilds.

2 strokes, are not particularly practical as an every day use motor, as these reliablitiy factors would not be tolerated in a street car for the masses.

Now for the above paragraph, substitute the word 2 stroke for rotary and suddenly the comparisons between a rotary and a 2 stroke become far clearer.

A rotary may be somewhat more reliable than a 2 stroke motor, however suffers from an inherently ineffecient design.

Great Thread.

Hang on, you used piston engine analogies first...that's why I used them after you, to counter your example. Note that my paragraph stating do not apply piston principles to define a rotary came after my analogies, for a reason: I don't like using them but when other people do it kind of forces me to. Now if you want to ignore my counter to that example, that's fine, we can call it a day on piston engine analogies and define the rotary for what it is...a rotary...with it's own measure of capacity...which hasn't changed for 30 years with good reason...and needs equivalence and relatives for the piston folk to get their minds around how fast that 1.3 litres of displacement is actually used inside the housing.

Want to talk virtual cylinders? Let's go back to my hypothetical rotary with 300 rotor faces and 300 chambers: half of them carrying a mixture of air and fuel ready to be ignited and the other half carrying exhaust gases...yet combustion only occurring in one of the 300 chambers at a time. So is it a...1.3 litre engine...or an unusually inefficient 130 litre engine? Note that I realise how impossible this rotary design may be; this hypothetical example simply highlights that just because the other faces are engaged in a part of the combustion cycle...does not mean they are combustion chambers. They are merely vessels doing the dirty work of the combustion chamber.

Whenever I see "muddying" I immediately assume it's either Gary under another users account or one of his students. It was a classic term of his translated to "I don't understand your analogy, you're trying to play with my head because I can't get around it". Racing classes are what half of this debate was about so let's not ignore that at all...the point of me comparing a two stroke piston to a four stroke piston is a flawless example of how we use measures of displacement outside of the everyday 4 stroke piston engine. Converting a 1.3 litre rotary engine to a 3.9 litre just so you can understand how a rotary's displacement works in piston engine terms is worthy of a childrens picture book. It is no different to saying a 1 litre two stroke is really a 2 litre because it completes twice as many combustion cycles in the same time as a four stroke...how ridiculous does that sound? In motorsport we use equivalence but we don't actually say the engine is really 2 litres when it's really 1 litre two stroke! And I'm not comparing rotaries to pistons here, it's piston to piston. If you so much as think of a piston engine when you're deciding rotary capacity for yourself then you're guilty of pistonism and suffering from a severe case of pistonitis.

  DRD-00F said:

My question about the compression test is probably still my favourite bit... if there were truly only 2 combustion chambers, then you would only have to turn the E shaft 360 degrees to do a complete compression test on the engine...

"If you were to do a compression test on a rotary, how many degrees would you turn the E shaft? If it's only got 2 ignition chambers it should only need 360 degrees yeah? That's 1 cycle yeah?? Cause a compression test only requires one cycle of the engine, any more and you're repeating yourself... and we all hate that right? "

A compression test is different in the rotary because there is more than one seal to the "cylinder" in a rotary housing. Two combustion chambers, 3 apex seals that come in contact with each combustion chamber. Alas, again, a rotary has a completely different setup in the way it's measured, applied and tested. You're applying a piston engine compression test based on there being only one seal in each cylinder. If you want to talk piston engines again, which I absolutely loathe doing, but it seems to be the only way to get a point across in this thread...if the piston in a cylinder had a face that somehow flipped around every combustion cycle you would have another set of piston rings which would need to be tested again for their seal...yet...the engine displacement and performance doesn't change because we are only changing the faces of the piston, not adding more combustion chambers to the engine.

[Birds]

  DRD-00F said:

He's taking the piss matt, calm down

Birds, stop posting... I see your slanty name down there!

Never! I fear that as long as people post in this thread I am doomed to a life of replying in it

[GT-R32]

Good post Birds. I really think you are taking the balanced view on this.

Can we stop calling a rotary a 2 stroke or even hinting it is one, please? It's not. Factually, it is not a 2 stroke. It's a Wankel. And its operation is closer to that of a 4 stroke.

[DRD-00F]

I'm so not replying to you Birds

Matt, I think the only person saying that left about 8 pages back

I personally think it's closer to a 2 stroke, but it's neither of those anyway, it's a Wankel...

I think 4 stroke is closer to being a skateboard then 2 stroke is... however you look at it, neither of them are a skateboard.

[bigslick]

  JayTay said:

From what i gather from reading so much of the excellent information and working out my own opinion, classes should work like this.

13b twin rotor (with 6 combustion faces in total) has an effective capacity of 3.9 litres. The same way a 6 cylinder piston motor (2 or 4 stroke) with an individual cylinder displacement of 654cc would displace 3.9 litres total.

I can't believe that is even up for debate.

Give the thing a 20% bonus for rubbish efficiency and the figure is still above 3 litres.

Rotaries are popular for motor racing as they have a massive class advantage.

To say that the effective displacement to be used for classing a 13B for racing should be 3.9 litres is ridiculous.

Have a think about it.

How much does a 2.6 litre 4 stroke displace in one turn of it's output shaft? 1.3 litres.

How much does a 1.3 litre 2 stroke displace in one turn of it's output shaft? 1.3 litres.

How much does a 13B displace in one turn of it's output shaft? 1.3 litres.

That's why all 3 engines would be classed in a similar way.

[iamhe77]

  bigslick said:

To say that the effective displacement to be used for classing a 13B for racing should be 3.9 litres is ridiculous.

Have a think about it.

How much does a 2.6 litre 4 stroke displace in one turn of it's output shaft? 1.3 litres.

How much does a 1.3 litre 2 stroke displace in one turn of it's output shaft? 1.3 litres.

How much does a 13B displace in one turn of it's output shaft? 1.3 litres.

That's why all 3 engines would be classed in a similar way.

Well that settles it then!

Where were you 40 pages ago, Ben?