Why Do Rotaries Suck?

[mad082]

  Cerbera said:

sorry, my bad... i explained it incorrectly, maximum capacity of a indiviual bank times by the number of banks

a full cycle using you theory of a 2.6L RB is actually 5.2L

no, using full cycle theory (a cycle being the amount of time it takes for every cylinder to fire, which in the case of a 4 stroke is 2 rotations) it is only 2.6L but using the 1 rotation of the crank theory it is 5.2L

  Cerbera said:

capacity (Volume) of a single rotor in a 13B at it's maximum is only ever 1.3L, times that by 2 and you get 2.6L... , you can never actually have 1.95L air by volume at any time in a single rotor like sydneykid suggests

you can never have 2L of air in a 2L piston engine at any point either, yet they are still classed as a 2L engine.

note: i was slightly off in my calculation earlier. a 2.0L 4 cylinder engine will have 1.5L of air in it at any time, not 1L.

[Birds]

  bozodos said:

I think the main problem is your continuing acceptance of the Mazda lies Birds

Quiet troll

  Smity42 said:

Well, that definitely gives you 3.9L then. 6 combustion chambers * .652L (i think?) per chamber = 3.9L.

But since a rotory takes 1080 degrees compared to 720 degrees of a 4 stroke, that would make it ROUGHLY the equivalent of 2.6L 4 stroke (3.9 * 720/1080), which I think we are starting to come to an agreement in this thread on?

However, by this logic, shouldn't we double the capacity of a 2 stroke?

If you treat the rotor as a single combustion chamber, you get 2 combustion chambers * capacity of entire chamber (~1.3L) = 2.6L.

No matter what way you swing it, you can't get 1.3L

I'm going to stick with calling it 3.9L, roughly equivalent to a 2.4L 4-stroke or 1.3L 2-stroke

We do double the capacity of a 2 stroke when comparing it to a 4 stroke

That's why the rotary engine when compared is often considered equivalent to a 2 stroke 1.3 litre or a 4 stroke 2.6 litre. Even though its full rotor combustion cycle uses 3.9 litres. Yes, we are starting to agree lol. It's not as difficult as this thread has made it out to be!

Anyway above all arguments and discussions, Wankel invented the rotary, he can say whatever displacement he likes. As long as all rotary engines are measured in the same way, it's irrelevant what displacement it is...we'll just use a different formula to work out what piston engine it should be run against in motorsport categories. End of story! Rotaries are their own engines and they can have their own rules.

[Mendoza]

Rotary's like piston engines do indeed suck, then squeeze, then bang, then blow

If you look at how far the rotary engine has come in a relatively short amount of time by very few engineers i think it's incredible. They might not be best suited for every application but the size and power to weight ratio are excellent.

I also like pepsi, fords and am just here to get my post count up

[DRD-00F]

^^^ This guy for president ^^^

[Smity42]

  Birds said:

We do double the capacity of a 2 stroke when comparing it to a 4 stroke

True lol, what I meant is we should double their actual measured capacity, ie call a 1.3L 2 stroke a 2.6L 2 stroke, since really each piston has 2 combustion chambers not one.

+1 to president vote

[SimonR32]

  mad082 said:

no, using full cycle theory (a cycle being the amount of time it takes for every cylinder to fire, which in the case of a 4 stroke is 2 rotations) it is only 2.6L but using the 1 rotation of the crank theory it is 5.2L

you can never have 2L of air in a 2L piston engine at any point either, yet they are still classed as a 2L engine.

note: i was slightly off in my calculation earlier. a 2.0L 4 cylinder engine will have 1.5L of air in it at any time, not 1L.

actually one rotation of the crank is 2.6L, two rotations of the crank is a full cycle and 5.2L

in a full combustion cycle of a rotor it actually takes in 3.9L for the 3 sides x 2 rotors that are full combusted, plus 2 extra sides on each rotor 1.3L by 2 remaining in the engine... so why don't we now call it a 6.5L by your reasoning

think about your second comment... your thinking about it the wrong way... capacity is max amount of air a single cylinder or rotor can hold times by the amount there are, not the whole engine at one given time

Edited September 23, 2009 by Cerbera

[Beer Baron]

seriously guys who gives a fk? the question was why do rotaries suck and the correct answer is they don't suck. they are a great engine. and just like any engine they need to be fitted to an appropriate car to really shine.

I would be one of the few people here who've actually owned and driven a number of GTRs from old 32s to whiz bang 35s and a 2001 FD 13BTT and I can tell you comparing any of them is a waste of time. they are all good. they all have different strengths and weaknesses and I can tell you a couple of "facts" from my own experience and from the way I drive.

My rotor was pretty thirsty. part of it may have to do with the fact that it has a tiny primary turbo which is on boost from about 2,000rpm and I like to have fun when I drive.

the 35 was pretty thirsty too, but they may have more to do with the cars weight, it's a good 500kg more than the RX7, that is staggering in itself.

my dead standard R34 GTR was not too bad. it's about 250kg heavier than the FD RZ I had and about 250kg lighter than the R35 and it was still not excellent.

I don't get why you have to hate one engine to like the other? there are differences between them. I don't give a f**k if the eccentric shaft multiplies the rotor RPM by a factor of 3. some girls may think my shaft is eccentric too but they have the decency not to laugh at it.

there is no easy way to express the properties of a rotor in the same way as a conventional 4 stroke combustion engine. because (read carefully) THEY ARE NOT THE SAME!

just accept that they are different. and yes it's a bit off that mazda try to express their stats in the same way as conventional engines, but who cares. what should they have done?

said, our wankel rotary (well elliptical) engine is a sort of 1.3-3.9l engine, and puts out up to 3,000 wanks per mintue which is roughly equal to 9.000rpm due to the nature of our eccentric shaft. please buy one.

they are a good motor but do need a lot of looking after if you want one to live, and I wouldn't rush out and stick on in my GTR or in my silvia, but it worked damn well in the FD RX7 that mine came in, just like the SR20 works damn well in the silvia and the VR38 does in the R35. in all cases engine and car are made to work well in harmony. and they do.

FD RX7 with it's stupid wankel engine. It is so choice. If you have the means, I highly recommend picking one up.

[DRD-00F]

I would buy any car that put out 3000 wanks per minute...

[spx25t]

I have one of each(Actually I have the skyline and my wife has the RX7)

R31 Skyline with a RB25DET (EMS computer, FMIC, 3 inch exhaust and Factory Turbo)

and a gen 1 RX7 with a 13B turbo (Microtech computer, FMIC, 2+1/2 inch exhaust and Standard Turbo)

both putting out around 180kw's at the wheels and I enjoy driving both of them for their different characteristics Skyline is great for its low down torque. and the mazda is great for its acceleration.

the big difference between them is about 300kgs. so my skyline has run 13.3 but I have yet to test the mazda due to Adelaide not having a 1/4 mile. But it definitely feels faster due to the weight advantage.

Edited September 23, 2009 by spx25t

[scathing]

Regarding the relevance of a rotary engine's eccentric shaft in determining "engine speed", I had a thought last night.

Out of curiosity, since rotary guys want to treat the engine as an "entire unit" and measure the speed of the enclosure's output medium, rather than the speed of what occurs inside it, how do they describe the gear ratios in a transaxle?

Lets say you have both a transaxle and a gearbox where the "shared" parts are physically identical. The difference is therefore the fact that the former has a final drive ratio inside the housing. For example's sake lets say that final drive is 3:1 (for poops and giggles).

In 4th gear of our hypothetical gearbox, the output shaft of the bell housing spins at the same speed as the input shaft. Its ratio is therefore 1:1. In the transaxle when you select the fourth available gear, the output shafts of that housing spins slower. Would rotary drivers describe the transaxle's 4th gear ratio as 3:1 instead?

[Birds]

I see the example you are trying to put forward scathing, and whilst it's a very good point, I'd like to point out that the 4th gear in the transaxle does have its own speed before interacting with the final drive. And for reference, yes, the final drive ratio in a transaxle is considered part of the "gearbox"...therefore if you are going to refer to the output speed of a transaxle you most certainly include the final drive ratio in the calculation. Hence the name transaxle is used instead of gearbox.

For all purposes of calculating vehicle speed you are going to be using crank/eccentric shaft RPM multiplied by gearbox ratio and diff ratio (or transaxle ratio in place of gearbox and diff), then multiplied by the size of the tyre.

Also the output shafts of a transaxle are the vehicle's driveshafts (straight to wheels), whilst the output of a gearbox is a tailshaft (straight to diff). The difference is that in the case of crankshafts and eccentric shafts, they are both used for the exact same output, i.e. movement just before the gearbox.

[ylwgtr2]

  scathing said:

Regarding the relevance of a rotary engine's eccentric shaft in determining "engine speed", I had a thought last night.

i also had a thought last night.....not about what goes round and round or what goes up and down....but what goes in and out....

[jase-r34]

  ylwgtr2 said:

i also had a thought last night.....not about what goes round and round or what goes up and down....but what goes in and out....

mmmmm those are some nice boobies!

It was about time someone got this thread back on track!

[scathing]

  Birds said:

I'd like to point out that the 4th gear in the transaxle does have its own speed before interacting with the final drive.

So does a rotor before interacting with the eccentric shaft.

  Birds said:

And for reference, yes, the final drive ratio in a transaxle is considered part of the "gearbox"...therefore if you are going to refer to the output speed of a transaxle you most certainly include the final drive ratio in the calculation.

The thing is, I'm not talking about the output speed of the transmission (which I'll use as a generic term that covers both the regular gearbox and the transaxle). I'm asking about how you'd enumerate the gear ratio if you had to put a value down for reference.

A gear ratio in a transmission, by unarguable definition, is the difference between its input value and its output value. So, what "output" do you take on a transaxle? That internal shaft speed before the final drive, or the shaft that leaves the housing? The effective gear ratio of a transaxle includes the final drive.

As an example, if you look at the brochure for the 370Z they have a table with the list of gear ratios, and a final drive ratio.

If Nissan were to print a similar table for the R35, for "accuracy" should they publish each the internal ratios multiplied with the final drive when they quote each gear (and either put a null value or repeat the diff drive again in the "final drive" row)?

  Birds said:

Also the output shafts of a transaxle are the vehicle's driveshafts (straight to wheels), whilst the output of a gearbox is a tailshaft (straight to diff). The difference is that in the case of crankshafts and eccentric shafts, they are both used for the exact same output, i.e. movement just before the gearbox.

The disagreement between what "cycling" piece of hardware relating to the engine is should be measured is at the heart of the "true RPM" debate the guys are having. Both are trying to demonstrate correctness.

Gary's arguing that an internal combustion engine's speed should be measured from the hardware that has direct physical contact with the combustion. The rotary guys are arguing that the powerplant's speed should be measured from the part of the powerplant that supplies said power to the rest of the powertrain.

The fact that they have different, but from my perspective both technically valid, reasons means they'll endlessly be debating tangentally to each other.

I'm trying to provide an analogy about whether you should be referencing "internal components" or "the output of the enclosure" to provide a numerical value for a component's behaviour. I thought I'd try and bring the two sides onto the same page, and move on to discussing something more interesting (and relevant) than what RPM an engine is technically doing.

[~rx3~]

  scathing said:

So does a rotor before interacting with the eccentric shaft.

Gary's arguing that an internal combustion engine's speed should be measured from the hardware that has direct physical contact with the combustion. The rotary guys are arguing that the powerplant's speed should be measured from the part of the powerplant that supplies said power to the rest of the powertrain.

just something else to argue about, i could be wrong, but if u measure engine speed from the hardware in direct contact with combustion a piston engine does no rpm as a piston moves in a straight line,also for a piston to stoke 100mm dosent the part of the crank that it is attached to have to move 314mm in a circle kind of like a 3 to 1 ratio.

[VB-]

in one revolution of the 'crank', a 13b will suck in 1.3l, it will compress 1.3l, and it will force 1.3l out the arse of it. ok, so its all happening on different faces of the rotor, but theoretically, its still moving the same amount of air as a 1.3 litre 2 stroke piston motor isnt it?

seems like gary is saying that one complete 'cycle' takes 3rpm in a rotor, thats where this figure of 3.9l is coming from? but its just not moving the same amount of air (horsepower) as a 3.9 2 stroke. a piston motor, 3.9l in capacity, 2 stroke, will move 3.9l per revolution of the crank, a 13b only moves 1.3l?

had a long day, might be large amounts of both math and brain fail in there ^

Edited September 23, 2009 by VB-

[DRD-00F]

  VB- said:

in one revolution of the 'crank', a 13b will suck in 1.3l, it will compress 1.3l, and it will force 1.3l out the arse of it. ok, so its all happening on different faces of the rotor, but theoretically, its still moving the same amount of air as a 1.3 litre 2 stroke piston motor isnt it?

seems like gary is saying that one complete 'cycle' takes 3rpm in a rotor, thats where this figure of 3.9l is coming from? but its just not moving the same amount of air (horsepower) as a 3.9 2 stroke. a piston motor, 3.9l in capacity, 2 stroke, will move 3.9l per revolution of the crank, a 13b only moves 1.3l?

had a long day, might be large amounts of both math and brain fail in there ^

That's only on one side of the rotor. What are the other 2 sides doing at the same time this is all happening? 1 full cycle is exactly that, the time it takes for each side of the rotor to go through the 4 phases of combustion. This equates to 3.9L of air. It's the same as every piston going through the same cycle. Completely fair comparison.

[Birds]

  scathing said:

So does a rotor before interacting with the eccentric shaft.

The thing is, I'm not talking about the output speed of the transmission (which I'll use as a generic term that covers both the regular gearbox and the transaxle). I'm asking about how you'd enumerate the gear ratio if you had to put a value down for reference.

A gear ratio in a transmission, by unarguable definition, is the difference between its input value and its output value. So, what "output" do you take on a transaxle? That internal shaft speed before the final drive, or the shaft that leaves the housing? The effective gear ratio of a transaxle includes the final drive.

As an example, if you look at the brochure for the 370Z they have a table with the list of gear ratios, and a final drive ratio.

If Nissan were to print a similar table for the R35, for "accuracy" should they publish each the internal ratios multiplied with the final drive when they quote each gear (and either put a null value or repeat the diff drive again in the "final drive" row)?

The disagreement between what "cycling" piece of hardware relating to the engine is should be measured is at the heart of the "true RPM" debate the guys are having. Both are trying to demonstrate correctness.

Gary's arguing that an internal combustion engine's speed should be measured from the hardware that has direct physical contact with the combustion. The rotary guys are arguing that the powerplant's speed should be measured from the part of the powerplant that supplies said power to the rest of the powertrain.

The fact that they have different, but from my perspective both technically valid, reasons means they'll endlessly be debating tangentally to each other.

I'm trying to provide an analogy about whether you should be referencing "internal components" or "the output of the enclosure" to provide a numerical value for a component's behaviour. I thought I'd try and bring the two sides onto the same page, and move on to discussing something more interesting (and relevant) than what RPM an engine is technically doing.

For starters, a rotor does not revolve and neither do pistons. Therefore it does NOT have its own RPM before the eccentric shaft. If I can't say it enough, revolutions per minute is a direct reference to the crankshaft and it always has been. So despite how diplomatic I usually am in arguments and debates there's actually no other valid argument for what engine RPM refers to...it's just a nice coincidence for people like Gary that pistons move at the same speed as the crankshaft because they are directly interacting components. That and the fact that almost every real world situation requiring an engine speed to calculate anything of relevance...runs off the crankshaft speed.

In contrast to pistons and rotors, all gears/crowns/pinions actually do revolve, so it is quite legitimate to state an individual gearbox component's ratio and RPM...even in a transaxle. But, if you asked me for the output ratio of a transaxle...I would be technically correct in telling you either a total reduction of 9:1 or a separate 3:1 for 2nd gear and 3:1 for the final drive. The former isn't adopted by manufacturers because gearbox and final drive ratio quoting has always been based on a traditional RWD style setup. Most people are familiar with being quoted separate ratios instead of a combined one. Also, you can still change the diff ratio in a transaxle, so it is still a useful and relevant piece of information to know exactly what the final drive is rather than just the total reduction of the transaxle. For lack of a better example, it's sort of like if Holden brought the Corvette in from America and quoted its top speed and acceleration times in MPH. This would be more correct for an American car but the Australian public want to hear what it can do in KM/H. Either way they will have the same time and top speed, just with different ways of saying it and one that is more accepted by the market than the other.

But, you do need to recognise that your comparison is void, simply because the output from a transaxle is a pair of driveshafts going to the wheels...where as the output from a gearbox is a tailshaft going to a diff. It's not just a different output speed, but an entirely different job...unlike the eccentric shaft in a rotary which IS the equivalent output of a crankshaft in a piston engine because they both share the same job - providing power to the gearbox. And yes, as I said before, transaxle has been given that name to imply that a differential is contained within the gearbox. A rotary is an engine, a piston engine is also an engine, but a gearbox is a gearbox and a transaxle is a transaxle

  ~rx3~ said:

just something else to argue about, i could be wrong, but if u measure engine speed from the hardware in direct contact with combustion a piston engine does no rpm as a piston moves in a straight line,also for a piston to stoke 100mm dosent the part of the crank that it is attached to have to move 314mm in a circle kind of like a 3 to 1 ratio.

This is the point I've been trying to convey. That not only can revolutions per minute NOT be applied to a piece of hardware that actually moves up and down...but the crankshaft in a piston engine has lobes that are its own version of the step up ratio on the rotary's eccentric shaft. These lobes are there not just for the conrods to turn the crank, but to provide the necessary torque/leverage for the conrods to turn the crankshaft. If you want to get technical with it...you can swap a piston engine crankshaft for one that strokes the displacement out...you can't do this with a rotary...so the eccentric shaft is in effect more a permanent part of the rotary engine than the crankshaft is in a piston engine. So with our stroker crankshaft...our displacement, torque and maximum engine speed changes...it's still the exact same engine though right? Right? Oops! Oops.

[ylwgtr2]

enough.....lets just wait till i finish my 250-300HP mazda factory PP engine 3924cc 3000rpm 2600cc,1308cc 9000rpm 450kg oscar sk90 racecar is finished and if the little hewland doesnt shit its pants and i dont stack it and if it doesnt blow it up and some spectator doesnt cop a 3000rpm or 9000rpm,654cc or 1962cc rotor in the mushki.....the lap times will tell if it sucks arse or not

Edited September 23, 2009 by ylwgtr2

[Birds]

Hahahahahaha!

"ahhh f***! I just copped a 9000rpm eccentric shaft to the head!"

"umm that was actually a 3000cpm rotor moron!"