Why Do Rotaries Suck?

[PM-R33]

Holy shit this thread got to 16 pages?!?! I gotta read this!

[topher_]

Well, this is pretty dissapointing I must say. 15 pages of fkn inane natter and not one picture of:

Cake

Matured cheese

Boobs

Pick your game up kunce.

Thanks for listening,

Ken

[BoyWhoCriedWolf]

sweet

[topher_]

Thread can now be locked.

[PM-R33]

Well just read all 16 pages, what a read. Definetely one of the most interesting threads lately. Gary dead set you should be on the Australian Debating Team or something lol. Keep it coming mate, very interesting stuff indeed. I for one never knew about this whole rotor debate and find it very interesting indeed.

I understand where both parties are coming from however Gary does make some sense of this all. After a bit of searching on the net, most of what he has said is backed up on similar topics about it all. The way i look at it, pretend piston engines didn't exist, therefore you can't compare anything to a piston engine. Compare it for what it is, an engine is a mechanical air pump where fuel is added and the spark is there to ignite it all to create a reaction and transform that engery into movement. When you think of it like that, his calculations and theory are spot on are they not?

[Sydneykid]

It's ENGINE RPM!!! Not rotor RPM, you measure horsepower, torque and RPM at the flywheel, not at the piston or rotor!!!

So what? The important rpm (or cpm if you prefer) is the combustion medium, that's the rotors and they only do 3,000 rpm. After all they are what produce the horsepower and the torque. The eccentric shaft is just the same as a gearbox output shaft, it changes the ratio between the combustion medium and the wheels.

Dictionary check

"An internal combustion engine cycle completed in two strokes of the piston."

"denoting an internal combustion engine whose power cycle is completed in one up-and-down movement of the piston."

"designating or having to do with an internal-combustion engine in which a complete fuel cycle in a cylinder requires only two piston strokes"

"A two-stroke engine provides power on every other stroke of the piston. It is the most common and affordable type of engine."

I can keep going, but I don't have the time...

You don't need to, just read what you posted, note the term cycle. Now go back an read what I posted.

And you fail to see the difference in potential energy... Try breaking it down into a single rotor engine vs a single piston 4-stroke engine to make it nice and simple for you, when the single piston engine finishes its combustion cycle it has no more potential energy stored, when a single rotor completes a combustion cycle it has two more combustion cycles in progress, hence still having potential energy!!!

But a single rotor engine has 3 combustion faces, so the best you can do is compare it to a 3 combustion face piston engine. a 2 stroke one at that. Even then it's not a good comparison, but go ahead if you feel you must.

I totally agree with you they should not be classed as a 1.3L 4-stoke engine because they are not... But they are not a 3.9L 2-stroke with 3000rpm on tap!!!

But they (a 13B that is) are a 3.9L 2-stroke rotary engine with 3,000rpm on tap;

1. they pump 3.9 litres in one complete cycle of the rotors, even Rice agrees with that fact.

2. they inlet at the same time as they exhaust on opposite sides of the rotor, just like any other 2 stroke/cycle engine. Are you saying they don't?

3. the rotors only do 3,000 rpm. We all know they do, so how could you dissagre with that fact?

What I didn't say and you seem to think that I did, was that "they are the same as a 3.9L 2-stroke piston engine with 3,000rpm on tap". That's not what I said, anywhere, anytime, in any post.

Cheers

Gary

[rgr34]

this thread is getting repetative lol time to put the subject to rest mayb? haha

[bigmikespec]

Far out Gary, try explain it in a cartoon or something, maybe more people will undertand that?

[camspeed]

Why do you all keep saying the rotors "do 3000rpm" ? Wouldn't it be correct to say the rotors do 1/3 the RPM of the eccentric shaft.

I know of rotors that regularly see 11000rpm or more on the track (when measured correctly from the eccentric shaft

[bigmikespec]

Why do you all keep saying the rotors "do 3000rpm" ? Wouldn't it be correct to say the rotors do 1/3 the RPM of the eccentric shaft.

I know of rotors that regularly see 11000rpm or more on the track (when measured correctly from the eccentric shaft

He is using it as an example, we know "your mates RX3" does 11000rpm measured incorrectly at the eccentric shaft.

[SimonR32]

Gary,

We are going nowhere so I'll just leave it at that!

But I'll ask you a question along a different line...

Why when you are refering to a combustion cycle in terms of RPM and combustion strokes of just one face of the rotor but suddenly when your talking about capacity you switch to talking about all 3 sides of the rotor...

A full combustion cycle would therefore be when all 3 sides of the rotor had completed their stokes, hense a even lower "RPM" (1000rpm) to fully claim that it's a 3.9L

[VB-]

Gary, why should rpm be measured at the rotor rather than the ececntric shaft? rpm in a piston motor its taken from the crank isnt it?

not trying to start arguments here, i just dont get where your coming from...

Edited September 22, 2009 by VB-

[scathing]

Gary, why should rpm be measured at the rotor rather than the ececntric shaft? rpm in a piston motor its taken from the crank isnt it?

From a technical perspective it was mentioned earlier in the thread that your tacho reads ignition pulses, so you're arguably "taking the RPM" value from the combustion chamber.

After reading through the thread, I think that Gary's taking the stance that you should be measuring the amount of air passed through one cycle of every combustion chamber. An engine is always described as an air pump when you talk about base principles, and so the action that directly involves air moving through the engine should be the guiding factor of how you should measure its behaviour.

In a piston engine that's a 1:1 ratio between the moving part of the combustion chamber and the crank but as far as Gary's concerned its a coincidence that they're the same. An engineer could have decided to stick a gear ratio in there "rotary style", but didn't. However, the fact that it is 1:1 has mislead people into quoting the speed of the wrong thing as a measure of engine behaviour, which happens to be correct by chance rather than comprehension.

My interpretation of Gary's perspective on the engine speed (and I'm not necessarily supporting it, just explaining from what I see as his perspective) is similar to the old "boost equals power" misconception. That is an erroneous conclusion based on incomplete or mislead understanding of basic principles.

Wind up the boost in most instances people have experience with and you see power gains, so certain people think the two are always directly related. However, in reality its air flow, not air pressure, that determines the power you can gain from tuning the induction system.

Feel free to correct me if I'm wrong Gary. I'm enjoying the thread, as hard as the slog has been at times, and feel like I'm learning quite a bit.

Edited September 22, 2009 by scathing

[SimonR32]

Wind up the boost in most instances people have experience with and you see power gains, so certain people think the two are always directly related. However, in reality its air flow, not air pressure, that determines the power you can gain from tuning the induction system.

actually it's air volume

[SimonR32]

But they (a 13B that is) are a 3.9L 2-stroke rotary engine with 3,000rpm on tap;

1. they pump 3.9 litres in one complete cycle of the rotors, even Rice agrees with that fact.

2. they inlet at the same time as they exhaust on opposite sides of the rotor, just like any other 2 stroke/cycle engine. Are you saying they don't?

3. the rotors only do 3,000 rpm. We all know they do, so how could you dissagre with that fact?

In my view if it counts for anything:

Engine RPM is the output revolutions of the of a complete engine. I don't believe you can base it on ignition (a rotor will actually use it's ignition twice during a single side of the rotor combustion cycle)

Capacity is the ability of a engine to hold a maximum volume of air at any given time. This definition works well for both a rotor and a piston engine and makes a 13B a 2.6L capacity!!!

It's not a 4-stoke, it's not a 2-stroke it's a rotarty...

Edited September 22, 2009 by Cerbera

[bozodos]

I can't wait to meet another rotary owner and inform them all about the 'mazda lies' which have been uncovered in this thread

[Smity42]

Rotaries are neither a 2 stroke or a 4 stroke, I'm sorry, but they do not have any pistons, so they are neither. There is no way around that. They are however MOST SIMILAR to a 2 stroke piston engine in how they operate.

A 4 stroke engine completes it's combustion cycle in 4 strokes of the piston - the classic suck squeeze bang blow.

A 2 stroke engine completes it's combustion cycle in 2 strokes of the piston - more or less suck-squeeze bang-blow (grossly innacurate simplification )

I don't even want to try and classify a rotary, but they are in fact neither. They are similar to a 2 stroke in the way they operate, using ports not valves, and that a single rotor is performing multiple parts of the combustion process at once.

On the other hand, they do perform a classic 4 stroke cycle in the form of suck squeese bang blow, on each face of the rotor.

2 stroke / 4 stroke, irrelevant, they are neither.

RPM, thats a tricky one. I tend to agree that the output shaft is the most appropriate way to measure RPM, but if someone were to put a 3:1 gear inside a piston engine to triple the output shaft velocity, where would you then measure it?

When you look at RPM in regards to the forces acting on the parts of the motor, well then it is really the 3000rpm the rotors themselves are doing compared to the ~6000 or whatever the pistons are doing. But then, a piston needs to actually stop and change direction, while a rotor just keeps spinning the same way, resulting in far less force anyway. But this is one of the ingenious things in the rotory design.

Capacity again, a tricky one. I personally would call it a 3.9L, but with the caveat that it compares more or less to a 4 stroke piston engine of 2/3 that. But I can see the points of the other arguments.

Basically it is very hard to compare piston to rotary motors as they are so different.

I am not a rotary fan boy, I love all types of engines, 2 stroke, 4 stroke, rotary, radial, jet. If it burns fossil fuel and moves stuff around, I like it.

Edited September 23, 2009 by Smity42

[SimonR32]

Rotaries are neither a 2 stroke or a 4 stroke, I'm sorry, but they do not have any pistons, so they are neither. There is no way around that. They are however MOST SIMILAR to a 2 stroke piston engine in how they operate.

A 4 stroke engine completes it's combustion cycle in 4 strokes of the piston - the classic suck squeeze bang blow.

A 2 stroke engine completes it's combustion cycle in 2 strokes of the piston - more or less suck-squeeze bang-blow (grossly innacurate simplification )

I don't even want to try and classify a rotary, but they are in fact neither. They are similar to a 2 stroke in the way they operate, using ports not valves, and that a single rotor is performing multiple parts of the combustion process at once.

On the other hand, they do perform a classic 4 stroke cycle in the form of suck squeese bang blow, on each face of the rotor.

2 stroke / 4 stroke, irrelevant, they are neither.

RPM, thats a tricky one. I tend to agree that the output shaft is the most appropriate way to measure RPM, but if someone were to put a 3:1 gear inside a piston engine to triple the output shaft velocity, where would you then measure it?

When you look at RPM in regards to the forces acting on the parts of the motor, well then it is really the 3000rpm the rotors themselves are doing compared to the ~6000 or whatever the pistons are doing. But then, a piston needs to actually stop and change direction, while a rotor just keeps spinning the same way, resulting in far less force anyway. But this is one of the ingenious things in the rotory design.

Capacity again, a tricky one. I personally would call it a 3.9L, but with the caveat that it compares more or less to a 4 stroke piston engine of 2/3 that. But I can see the points of the other arguments.

Basically it is very hard to compare piston to rotary motors as they are so different.

I am not a rotary fan boy, I love all types of engines, 2 stroke, 4 stroke, rotary, radial, jet. If it burns fossil fuel and moves stuff around, I like it.

simon likes this!

except for the 3.9L, it has a capacity of 2.6L... yes it uses 3.9L in complete combustion of all the rotors but it only every has the capacity (volume) of 2.6L

[DRD-00F]

Capacity is the ability of an engine to hold a maximum volume of air at any given time. This definition works well for both a rotor and a piston engine and makes a 13B a 2.6L capacity!!!

Well there's another person...

At least we've moved on from 1.3L, that's a good start. But it's still not correct.

Your reasoning here would make an RB26 less then 2.6 litres. You have taken a moving item and stopped it, taken a freeze frame of the moment that it would hold (assumedly) the most amount of air at one time. Thanks to the differentiating strokes of the pistons in the RB26 engine (and any other piston engine) this would mean that there is NO SINGLE POINT that there would be 2.6L of air inside the engine. The 2.6L calculation is taken from one full 'cycle' of all the pistions, as is the 3.9L in the rotary.

But I could be wrong.

[mad082]

the big problem i see with a lot of peoples argument (those saying it's only 2.6L) is this: they are classing it as a 2.6L becuase it has only fired 2 sides of the rotor for the same duration as a piston engine would for a full cycle (2 rotations in the case of a 4 stroke). however the big flaw in this is the comparison. the simple fact is that a 2 stroke and a 4 stroke engines have their capacity based of the same theory despite the fact that a 2 stroke firing every cylinder on every stroke and the 4 stroke only having fired on half the cylinders during the same stroke. so it is only fair to then extend the same principle to rotaries who will only have complated 2/3 of a cycle in that time.

if you want to class a 13b as 1.3L on the argument that there has only been 1 combustion per rotor per rotation of the crank/eccentric shaft then you also have to class a 4 stroke as only half it's given displacement and the only engine you can class as it's full given displacement is a 2 stoke. you either class engines by displacement of chambers combusting on 1 rotation of the crank/eccentric shaft or you class it as total displacement of all combustion chambers regaurdless of the amount of rotations of the crank/eccentric shaft makes for one full cycle of the engine. 1 rule for all, not just bending the rules to make 1 seem better.

even with people (the mazda fans) saying that if calculated the same way as a 4 stroke the displacement would be 2.6L, they themselves are admitting that mazda has basically lied by calculation the displacement in a way that benefits them.

i will agree with them though on the fact that a rotary is 'similar' to a 2 stroke, but not the same.