Why Do Rotaries Suck?

[Beer Baron]

I never knew my RX7 was a 3.9 litre elliptical engine produced 230rwkw at 3,000rpm. first turbo must be kicking in at 800rpm and second one at 1800rpm holding strong to the 3,000 range. I like engines. I like my RX7s 13BTT, I like the SR20 in my silvia and I love the RB26s in my GTR. hey the VR38TT in my R35 was pretty kick ass too. getting an EP3 civic type R soon and I love the 2litre 4 pot in them too. I guess I just like engines. they all have their strong and weak points.

my 13b would possibly break if I look at it the wrong way. so will my RB26.

the SR20 don't like too much revs and may decide to break rocker arms just to piss me off.

the 13b and the RB26 drinks fuel like it's zohan drinking a fizzy bubbler

the NA EP3s motor lacks that fat midrange my turbocharged motors have.

the VR38 is just too good at what it does and in some ways that's depressing too.

I quite like the whateverthefk engine is in my nissan atlas truck too. it makes a massive 98kw but has some giant torque figure and for it's purpose it's perfect. and it's a 4.2l 4 cylinder and it has a redline of about 3,000 too. don't think it works the same as a 3.9l 3,000rpm rotor though....

[Sydneykid]

The biggest problem here is that Sydneykid is enginist.

I like that word, "enginist", thanks, I might continue to use it.

He feels that all engines should conform and assimilate to the white man's piston engine.

Not true, I just object to Mazdas 40 years of lying.

No rotary should be allowed to compete with pistons in motorsport because they are not the same, they are not equal.

Again not true, what I object to is Mazdas 40 years of lying. As a result rotaries have been able to compete unfairly in all forms of motorsport. It's cheating, gross cheating and that's what I don't like.

All rotaries do is influence our children through their terrible exhaust note that can hardly be called music. They should all move out of the Mazda wreckers and get real jobs like driving trucks, just like piston engines. Piston power, piston power!

You really don't know me very well at all, right at the moment I am working on a rotary engined car with another rotary on a engine stand next to me.

As I said before, if it is true about Mazda "lying" (which it isn't, because it has been pointed out numerous times in this thread that comparing rotary engines to piston engines based on the characteristics of a piston engine is nothing short of ridiculous),

I haven't compared the method of measuring the capacity of a rotary with the method of measuring the capacity of a piston engine. All I have done is measure the proper capacity of a rotary engine. The fact is a 13B pumps 3.9 litres of air in one revoltion of the rotors, that's an irrefutable fact. Hence it's a 3.9 litre rotary engine, indesputable mathematics. There is no argument. There is also no argument that the rotors rev at 3,000 cpm, another irrefutable fact. Yes, I used cycles per minute as someone objected to the term revolutions being applied to a rotary, not that it matters in this context.

I agree that comparing a rotary engine with a piston engine is fraught with difficulties. But that's irrelevant to the fact that a 13B is a 3.9 litre engine that revs at 3,000 cpm. If you want to debate those facts then let's do it, don't try muddying the water with irrelevancies.

the only people who would give a shit about this are involved in motorsport.

That's me.

The only thing that matters in the real world (i.e. consumer markets) is the perceived value of the engine.

Surely that isn't a positive, because rotary's general public perceived value would be zero. Unreliable, expensive to maintain, lousy fuel ecomomy and a big polluter would be the most common terms applied.

For an engine only produced by one manufacturer in one model at a time there sure are alot of rotaries still around.

For 40 years

Cheers

Gary

[Birds]

Agreed Streeter.

Where they are allowed to compete, homologation takes note of their advantage and attempts to correct it as best it can through estimation of this advantage in the form of a displacement ratio. You can only compare rotary and piston engines on the end product they produce...anything in between...the workings of them...it's friggen pointless.

/thread.

[ylwgtr2]

were onto somthing here.....tacho's should read in piston speed

[Sydneykid]

The point is that how the ignition affects the drive shaft is what's important.

But there's a gearbox in between the engine and the driveshaft. So how we measure the engine rpm depends on what gear the box is in? Surely not!.

That's the problem, the gear ratio between the rotor and the eccentric shaft is exactly that, a gear ratio. It's purpose is exactly the same as a gear ratio in a gearbox or a diff ratio. That is quite simply to change the ratio between the number of revolutions (cycles if you prefer) of the rotors and the number of revolutions of the tyres. Whether that gear ratio is inside the engine, inside the gearbox or inside the diff doesn't matter, it's still just a gear ratio, nothing more.

The fact remains, the rotors are doing 3,000 rpm, an indesputable, irrefutable fact.

In the case of a rotor the rotor itself ingites 3 times per revolution but the eccentric shaft is only rotated by one of these ignitions for it's revolution. The exact same effect as a two-stroke. This is what mazda seem to have based their definition of a 1.3ltr high revving engine on.

No it's not, go and read the original books on rotaries. What Mazda did was take the capacity of one chamber, like it was a cylinder in a piston engine. The rotor is then a piston in that cylinder. Hence a 2 rotor engine's capacity is simply the capacity of one cylinder multiplied by 2. They conveniently ignored the fact that each rotor has 3 combustion "sides", unlike a piston that has one. For those of you complaining about comparisons to piston engines, well Mazda started it with how they measured the capacity.

I somewhat agree with their definition because the driveline is what affects how the power is output, the fact that the rotor spins three times slower can either be viewed as being similar to having more pistons or as mazda would like to see it, the same "pistons" on their next cycle.

How does the number of piston/cylinders change the rpm? I'm confused.

You're right though, comparisons to piston engines don't really mean anything... unless you're trying to figure out what category rotarys should be lumped into for motorsport.

And therein lies (sorry) the problem. A 3.9 lite engine has been competing illegally as a 1.3 litre engine for far too long.

Cheers

Gary

[Birds]

I think we should remove the lobes from a piston engine's crankshaft. It provides the piston engine with an unfair torque advantage in turning the crankshaft, just like the rotary engine with it's 3:1 eccentric shaft gear ratio. Then again, a piston engine wouldn't get far without the lobes would it...hold on...neither would a rotary without it's gear ratio. Also, should we take engine REVOLUTIONS per minute from the product of the engine, i.e. the crankshaft, which just happens to be relevant to whatever application we use the term RPM in...or should we take revolutions from the parts that move up and down...and in the case of rotaries...orbit eliptically. Changing it from revolutions per minute to cycles per minute gives the argument a very different meaning...no one is disputing that an eccentric shaft turns at 3 times the speed of the rotors...given we were originally talking about engine RPM, i.e. a crankshaft, you are incorrect.

[gotRICE?]

This is awesome.

No matter what gets thrown, Gary throws back.

If it waas me i would have gotten pissed off and given up long ago!

[Birds]

Of course he throws back, I could have told you from his first response that this thread would go on and will continue to go on for pages and pages. You can pick the kind of people who will do it (I'm one of them). A stubborn mule + tired rhetoric that originally stemmed from a case of devil's advocate + selectively responding to argument = a debate that's never settled courtesy of ego. Welcome to the internet.

[Sydneykid]

Not that it has anything to do with this thread by my versions of the baron's post.

I always knew an RX7 was a 3.9 litre elliptical engine that produced 230rwkw at 3,000rpm. first turbo kicking in at 800rpm and second one at 1800rpm holding strong to the 3,000 range. It's blatantly obvious.

I like engines,. I like the RX7s 13BBP, I like the RB31DET in my Skyline and I love the 3 Litre straight 6 in my M3. Hey the RB25DET in my Stagea is pretty kick ass too. Working on an Evo X 4G63 on and off, plus getting an Evo 7/8/9 soon and I love the 2 litre 4 pot in the Integra TR's. I guess I just like engines. they all have their strong and weak points.

the 13BBP's break if I look at them the wrong way.

the RB31DET don't like too much revs and may decide to break an oil pump just to piss me off.

the 13BBP's and the RB31 drink fuel like it's me on a Jack Daniels

the NA K20A motor lacks that fat midrange, but its getting a 2.4 litre crank to fix that.

the M3 is just too good at what it does and it's never depressing, I love the song of a BMW I6.

I quite like the Cummins 12 litre VGT (variable geometry turbocharger) that is in the race team transporter. It has 1600 ftlbs of torque and 425 bhp and for it's purpose it's perfect. It has a redline of about 2,500 too, so I think it works the same as a 3.9l 3,000rpm rotor, except it's not a 2 stroke.

Cheers

Gary

[Sydneykid]

Of course he throws back, I could have told you from his first response that this thread would go on and will continue to go on for pages and pages. You can pick the kind of people who will do it (I'm one of them). A stubborn mule + tired rhetoric that originally stemmed from a case of devil's advocate + selectively responding to argument = a debate that's never settled courtesy of ego. Welcome to the internet.

Ah excellent, since you have decideed to attack the man not the argument I assume that means you have lost and give in. Understandable, since I'm right and eventualy that reality dawned on you.

Cheers

Gary

[iamhe77]

Of course he throws back, I could have told you from his first response that this thread would go on and will continue to go on for pages and pages. You can pick the kind of people who will do it (I'm one of them). A stubborn mule + tired rhetoric that originally stemmed from a case of devil's advocate + selectively responding to argument = a debate that's never settled courtesy of ego. Welcome to the internet.

Aaahhhh. So that's what this internet thingy is for! Cheers Birds!!

[Birds]

Ah excellent, since you have decideed to attack the man not the argument I assume that means you have lost and give in. Understandable, since I'm right and eventualy that reality dawned on you.

Cheers

Gary

Apologies if you took that as a personal attack, it wasn't intended to be as such...I was merely describing people like you and I. Far from feeling I've "lost" or wanting to "give in" (I don't see this as a game you can win or lose, just a search for truth and I'm not here to be wrong or right), I can't be bothered further arguing my points when 50% of them (incidentally the most important ones) are being ignored by yourself.

Birds out.

[Sydneykid]

Apologies if you took that as a personal attack, it wasn't intended to be as such...I was merely describing people like you and I. Far from feeling I've "lost" or wanting to "give in" (I don't see this as a game you can win or lose, just a search for truth and I'm not here to be wrong or right), I can't be bothered further arguing my points when 50% of them (incidentally the most important ones) are being ignored by yourself.

Birds out.

OK, let's break this down into 3 simple questions and answers;

Firstly RPM, I have stated that the rotors only do 3,000 rpm, are you denying that is correct?

Next capacity, a simple question really, how much does a rotary engine (say a 13B) pump in a complete cycle of it's 2 rotors? The answer is 3.9 litres, surely undeniable isn't it?

Lastly rotary = 2 stroke, again a very simple question. A rotary inlets, compresses, combusts and exhaust in one revolution of the rotor. If that is true, and it is, then they are a 2 stroke, agree?

These are my 3 statements, simple and concise, no muddy water. You either agree or dissagree, if you dissagree then please tell me why.

Now which 50% of your arguments am I ignoring?

Cheers

Gary

[Birds]

I don't deny the rotors orbit 3000 times per minute while the eccentric shaft is doing 9000rpm. But when someone asks me the engine rpm of a rotary engine, I will quote them the eccentric shaft speed because that is where engine rpm is forever relative and relevant.

As for displacement, I ask you...how much air does the 13B pump in a complete cycle of it's eccentric shaft? The air travelling through a rotor in its complete cycle is irrelevant, because the engine's crankshaft revolves thrice in that time. If you want to compare rotors to pistons for air intake, you need to compare their air intake to crankshaft revolution because that is the only thing these engines share in common and that is what Mazda's figure is based on. Follow this formula and we get 1/3 of the 3.9 litres you quote these engines as having. Surprise, surprise...the 13B uses 1.3 litres of air for every turn of the eccentric shaft. Just like a four stroke piston engine (let's say 2 litres displacement) will use 2 litres of air for every rotation of its crankshaft.

Now further to this, given every measurement of rotary engine displacement has always been based on Mazda's original formula, how can Mazda possibly be lying about anything? Everyone knows what a 1.3 litre rotary engine is capable of. Everyone knows what a 2.0 litre rotary engine is capable of. Should another manufacturer build a rotary engine the same capacity as the 13B it will also be considered to have 1.3 litres displacement, and no one will care. Everyone knows that the 1.3 litres of a rotary engine is different to the 1.3 litres of a naturally aspirated four stroke piston engine...I learnt this one looking through my Mazda car show brochures when I was 8 and I'm not that bright.

I would never call a rotary any sort of stroke because it's combustion cycle doesn't move in a stroke. Stroke is a term that refers to movement of a piston, i.e. up and down. Rotary is around and around. The differentiation between two and four stroke is the number of strokes the piston must make to complete the combustion cycle...well in a rotary you can call it one stroke if you like. But given they have three combustion chambers in the one moving part...just another reason I think it is ridiculous comparing rotors to pistons and basing this comparison on the science of piston engines. You need to acknowledge that rotaries are so different that they need to have their own rules...it doesn't matter what Mazda want to say about them or what people want to believe about them.

Your argument seems to be based on the eccentric shaft not playing a part in any comparisons, when in fact it is the only thing giving these engines anything in common.

[ylwgtr2]

they lied there way to international engine of the year in 2004

Edited September 18, 2009 by ylwgtr2

[martyt]

I actually have never owned a rotary engine, but I 100% with the above comments from birds. I think the main arguments against the rotary are really just anti-rotary gripes.

Argument 1 : They are inefficient. Most people assume efficiency though use of fuel = petrol. But this is just wrong. everyone says " thats a lot of fuel to use for a 1.3 litre engine" assuming that its a cylinder engine. the 1.3 litre capacity means very different things in the 2 completely different engine types.

Argument 2 : They are unreliable. What is actually unreliable about an engine that if you maintain as per the manufacturer's instructions, will last as long as the manufacturer's stipulated warranty?

[rgr34]

I don't deny the rotors orbit 3000 times per minute while the eccentric shaft is doing 9000rpm. But when someone asks me the engine rpm of a rotary engine, I will quote them the eccentric shaft speed because that is where engine rpm is forever relative and relevant.

As for displacement, I ask you...how much air does the 13B pump in a complete cycle of it's eccentric shaft? The air travelling through a rotor in its complete cycle is irrelevant, because the engine's crankshaft revolves thrice in that time. If you want to compare rotors to pistons for air intake, you need to compare their air intake to crankshaft revolution because that is the only thing these engines share in common and that is what Mazda's figure is based on. Follow this formula and we get 1/3 of the 3.9 litres you quote these engines as having. Surprise, surprise...the 13B uses 1.3 litres of air for every turn of the eccentric shaft. Just like a four stroke piston engine (let's say 2 litres displacement) will use 2 litres of air for every rotation of its crankshaft.

Now further to this, given every measurement of rotary engine displacement has always been based on Mazda's original formula, how can Mazda possibly be lying about anything? Everyone knows what a 1.3 litre rotary engine is capable of. Everyone knows what a 2.0 litre rotary engine is capable of. Should another manufacturer build a rotary engine the same capacity as the 13B it will also be considered to have 1.3 litres displacement, and no one will care. Everyone knows that the 1.3 litres of a rotary engine is different to the 1.3 litres of a naturally aspirated four stroke piston engine...I learnt this one looking through my Mazda car show brochures when I was 8 and I'm not that bright.

I would never call a rotary any sort of stroke because it's combustion cycle doesn't move in a stroke. Stroke is a term that refers to movement of a piston, i.e. up and down. Rotary is around and around. The differentiation between two and four stroke is the number of strokes the piston must make to complete the combustion cycle...well in a rotary you can call it one stroke if you like. But given they have three combustion chambers in the one moving part...just another reason I think it is ridiculous comparing rotors to pistons and basing this comparison on the science of piston engines. You need to acknowledge that rotaries are so different that they need to have their own rules...it doesn't matter what Mazda want to say about them or what people want to believe about them.

Your argument seems to be based on the eccentric shaft not playing a part in any comparisons, when in fact it is the only thing giving these engines anything in common.

this thread is nuts by the way lmao..... i dont have anything to add as my knowledge is basic but for what its worth the above to me makes the most sense in regards to explaining and making some type of comparison between the 4 storke piston engine and rotary engine...

Edited September 18, 2009 by rgr34

[Sydneykid]

I don't deny the rotors orbit 3000 times per minute while the eccentric shaft is doing 9000rpm. But when someone asks me the engine rpm of a rotary engine, I will quote them the eccentric shaft speed because that is where engine rpm is forever relative and relevant.

OK so you agree with me that the rotors only do 3,000 cpm. Let's leave it at that and carry on.

As for displacement, I ask you...how much air does the 13B pump in a complete cycle of it's eccentric shaft? The air travelling through a rotor in its complete cycle is irrelevant, because the engine's crankshaft revolves thrice in that time. If you want to compare rotors to pistons for air intake, you need to compare their air intake to crankshaft revolution because that is the only thing these engines share in common and that is what Mazda's figure is based on. Follow this formula and we get 1/3 of the 3.9 litres you quote these engines as having. Surprise, surprise...the 13B uses 1.3 litres of air for every turn of the eccentric shaft. Just like a four stroke piston engine (let's say 2 litres displacement) will use 2 litres of air for every rotation of its crankshaft.

So you agree that a 13B pumps 3.9 litres in one complete cycle of it's rotors.

Now would you like to go back and check the 2 litre 4 cylinder 4 stroke engine pumping 2 litres for every rotation of its crankshaft? It actually pumps 1 litre, it takes 2 revolutions of the crank to pump 2 litres. So using your logic of eccentric shaft revolutions somehow making a difference to an engine's capacity, then a 2 litre piston engine should really be rated as 1 litre. Now I don't know about you, but I don't do that for a piston engine so why should you expect anyone to do it for a rotary engine.

The lies started when Mazda convinced the Japanese registration authorities to only measure one side of the rotor. This resulted in two things, firstly cheaper registration because rego in Japan was based on engine capacity. Secondly it was marketing trick, small engine lots of power. Once the lies started they couldn't stop and so they spread to motorsport, which is where I have the most problem.

Now further to this, given every measurement of rotary engine displacement has always been based on Mazda's original formula, how can Mazda possibly be lying about anything? Everyone knows what a 1.3 litre rotary engine is capable of. Everyone knows what a 2.0 litre rotary engine is capable of. Should another manufacturer build a rotary engine the same capacity as the 13B it will also be considered to have 1.3 litres displacement, and no one will care. Everyone knows that the 1.3 litres of a rotary engine is different to the 1.3 litres of a naturally aspirated four stroke piston engine...I learnt this one looking through my Mazda car show brochures when I was 8 and I'm not that bright.

You believed the lies, that's OK you were only 8.

Back to your point, it's only unfair when a supposed 1.3 litre rotary engine is compared to 1.3 litre piston engine. That's where Mazdas marketing was aimed at, that's where their motorsport homologation was targeted. And it's all based on untruth, even using Mazdas "formula" it should be 2.6 litres. Using any logic of an air pump, which after all is what an engine is, it's a 3.9 litre.

I would never call a rotary any sort of stroke because it's combustion cycle doesn't move in a stroke. Stroke is a term that refers to movement of a piston, i.e. up and down. Rotary is around and around. The differentiation between two and four stroke is the number of strokes the piston must make to complete the combustion cycle...well in a rotary you can call it one stroke if you like. But given they have three combustion chambers in the one moving part...just another reason I think it is ridiculous comparing rotors to pistons and basing this comparison on the science of piston engines. You need to acknowledge that rotaries are so different that they need to have their own rules...it doesn't matter what Mazda want to say about them or what people want to believe about them.

You are confusing the meaning of "stroke" (up and down) in relation to an engines "cycle", it is quite common to replace the term "2 stroke engine" with "2 cycle engine". You are doing exactly what you accuse me of, trying to compare a piston engine with a rotary. Don't do it, think of it as a rotary engine, forget pistons and up and down. Now if you still have a problem with the term "stroke" being applied to a rotary then substitute it with "cycle". So back to the question, is a rotary a 2 cycle engine? The answer is yes it is, absolutely.

Your argument seems to be based on the eccentric shaft not playing a part in any comparisons, when in fact it is the only thing giving these engines anything in common.

I'm sorry I don't understand, piston engines have crankshafts, rotaries have eccentric shafts so there is nothing common there. Why are you trying to make something that is inherently different somehow the same when the fact is they aren't.

Cheers

Gary

[_Ryan_]

i was thinking this myself today... was on the freeway with a clean FD... some old guy driving.

i guess it's just too alternative for a lot of people

I want an FD, figured a 32 was a good alternative on traineewage... revy, torqueless, handles decent, RWD

[myRB25DETT]

woww, this is the sh!t right here...i didnt know forum like this could be much fun.. now im learnin...keep it comin boys..at least i could use some of these info. when arguing with my mates Rx7 comparing my GTT to his one...lolz...this is GOLD ....