Why Do Rotaries Suck?

[gotRICE?]

I enjoyed that read. Learned alot. Keep it coming!

*subscribed*

[KezR33]

Add it all up and you find the truth is a pretty average engine, with only one advantage and that’s small external size.

But what an advantage is it! This is what I'm trying to point out. I don't care what sort of displacement it has vs. a piston engine, just the sheer power to weight (engine weight) or power to size ratio.

Imagine if they just kept adding rotors till the engine was the same weight as an LS9, I have no idea how long or feasible this would be, but why not?

Picture a 10 (I don't know the terminology for 10) rotor engine. If a Quad is 20B, this thing can be a 90C. Surely they could fit this into a two seater rear mount sports car, or a long nosed beast like a Dodge Viper.

Wouldn't that thing be truly scary on the road, despite being a heavier car?

Edit: What if they expanded the diameter of the rotors too? I still think the engine theory has a ton of potential that most likely technology hasn't caught up with.

[jase-r34]

This has been a great read! Gary, I am in total agreement with you on all points. Especially the 2 stroke fact. I have tried to argue that point to many a rotor mad nutcase lol, but I just don't have the way with words that you do!

All in all though, even if rotors were as good in every way as a piston engine (which they definitely are not) I would still never like/own one as I HATE the noise they make.

What a shame the series 6 RX7 has the old wankel in it. Such a sexy car.

[KezR33]

This has been a great read! Gary, I am in total agreement with you on all points. Especially the 2 stroke fact. I have tried to argue that point to many a rotor mad nutcase lol, but I just don't have the way with words that you do!

All in all though, even if rotors were as good in every way as a piston engine (which they definitely are not) I would still never like/own one as I HATE the noise they make.

What a shame the series 6 RX7 has the old wankel in it. Such a sexy car.

Find one with a blown motor. 2J conversion

[TALBO]

If a triple is 20B, this thing can be a 90C. Surely they could fit this into a two seater rear mount sports car, or a long nosed beast like a Dodge Viper.

.

Fixed. Remember a PP quad rotor 26B won LeMans many years ago, then banned!

[KezR33]

Fixed. Remember a PP quad rotor 26B won LeMans many years ago, then banned!

Damn. So wait. 26 = 4 rotor. 26*2.5 = 65 = 10 rotor.

So it's a 65C (don't ask me where I got 90 from before, lol).

No going by the earlier theory that a 13B is really a 3.9L piston equivalent. This means that the 6.5L rotary is really a 19.5L engine.

Now if you could actually fit a 19.5L engine into a car, tell me it wouldn't annihilate everything.

[typevu]

It would certainly annihilate your wallet from fueling up so many times!

[scathing]

But what an advantage is it! This is what I'm trying to point out. I don't care what sort of displacement it has vs. a piston engine, just the sheer power to weight (engine weight) or power to size ratio.

You need to evaluate totals, not just a small fraction. If you want to talk about size and weight, you also need to consider the far larger fuel tank a rotary requires.

Inside a car, the fuel inside tank is also a mass that changes as the vehicle runs, which means the car's weight distribution changes as you drive. In a performance car, that's a bad thing. You could locate the fuel tank close to the centre of gravity to reduce this effect, but with the tank in a rotary needing to be bigger for a given range that's more difficult.

Also, torque and total area under the power curve are also things to consider when you're talking about performance. Not just power vs weight or size.

Picture a 10 (I don't know the terminology for 10) rotor engine. If a Quad is 20B, this thing can be a 90C. Surely they could fit this into a two seater rear mount sports car, or a long nosed beast like a Dodge Viper.

The more chambers you put in, the greater the load on the eccentric shaft. Like piston engines, you can only go so far inline before you break it. Hence why you can't string a dozen chambers together.

Wouldn't that thing be truly scary on the road, despite being a heavier car?

Overladen trucks are heavy and scary. It doesn't make them good.

Edit: What if they expanded the diameter of the rotors too? I still think the engine theory has a ton of potential that most likely technology hasn't caught up with.

Mazda's should have an all alloy housing and direct injection but I suspect they'll still be playing catch-up in practically every respect compared to piston engines.

[GTR-32U]

They suffer from the lies that Mazda spun back in the 70's.

Lie #1, they are a 4 stroke engine, rubbish they are a 2 stroke. Every one knows it, but Mazda lied because they didn't want the "lawn mower syndrome" attached to rotaries. The fact remains they are really a 2 stroke. The fact that they need oil in the petrol is just another nail in the 2 stroke coffin.

Lie #2, they rev to 9,000 rpm. no they don't. The rotors only do 3,000 rpm they use a step up gear ratio to spin the eccentric shaft at 3 times the rotor rpm. Why? So they could use normal piston engine gearbox and diff ratios. They could have easily used say 6 to 1 rotor to shaft ratios, then claimed 18,000 rpm. The rotors would still only be doing 3,000 rpm, their true rpm.

Lie #3, the biggest lie, the small engine capacity eg; a 13B is 1.3 litres. What a whopper of lie that was. Their true capacity is 3.9 litres, 2 x 3 sided rotors x .66 litre each side = 3.9 litres. Everyone knows it, but Mazda persisted with the lie.

As with most things, the lies came back to bight Mazda. They use a lot of petrol for a 1.3L 4 stroke. But not so much for a 3.9 litre 2 stroke. They take a big turbo for a 1.3L 4 stroke, it's not so big when the truth is 3.9 litre 2 stroke. They produce an impressive amount horsepower per litre when using the lies of a 1.3L 4 stroke. But when the truth is used, it's a shit house power output for a 3.9 litre 2 stroke.

So put the lies away and look at rotaries in the true light of day. As a 3.9 litre 2 stroke (in the case of a 13B) they have OK horsepower output, but lousy torque output due to their poor combustion chamber shape. That's why they need 2 spark plugs. Another reason for their poor torque output is the compression ratio, which is very low, another result of that poor combustion chamber shape. Their fuel economy is OK for a 3.9 litre 2 stroke, but they don't use the fuel efficiently, hence poor power output per litre of fuel used. They respond well to turbocharging as you would expect from a 3.9 litre 2 stroke with a low compression ratio.

Add it all up and you find the truth is a pretty average engine, with only one advantage and that's small external size. But the fact is it's not user friendly size. They don't fit well in a front wheel drive application compared to a compact inline 4 cylinder. They don't offer much space saving in a rear wheel drive application as they need a radiator, oil cooler and gearbox big enough for a 3.9 litre 4 stroke. A compact 3.9 litre V6 doesn't need any bigger engine bay and yet produces more horsepower, more torque and gets better fuel economy.

But back to real reason for rotaries tiny niche market, the Mazda lies from the '70's. Take them away and they become a much more believable engine alternative.

Cheers

Gary

wow .,...really great read here.Nothing against Rotors personally, But I am forever hearing from the Rotor guys how Piston engines dont rev. And I love to reply that Rotor engines dont Rev. They kind of look at me with a weird look until I explain a few facts. Rotor engines have few or no parts that have to completely change direction. Whereas a piston engine, Both Rods and pistons have to completely change direction every stroke, As does valves. Yet they boast of 9000 rpm on worked motors when S2000's will spin to 9000 rpm off the showroom floor.Then I throw in the 18000 rpm Formula 1 engines....It does kind of make them sad

[ylwgtr2]

those who dont like the sound....have a listen to this

ive had rotaries for years and ive only killed one engine(and that was from running it out of oil!)It had 300,000klms on it and was an unopened block......they are a fantastic thing,i can pick them up on my own.our B2200 delivery ute has one in it.Its a full chassis ute so its quite heavy and i will tell you one thing....i have loaded that thing up with that much weight that it was riding on the bump stops from time to time and i could short shift the thing no worries..it has the same diff and gearbox as when it was piston powered and altho i must admit its fuel consumption is not very good it by far out performs both its previous engines (gasoline and diesel) the diesel was just plain old shite throughout the whole rev range,with the gasoline engine i would have to belt it down through the gears with a load on up the hills and and hold it to the boards and hope the crank didnt fall out of it....i do have to downshift a gear with the 13b with a load on up a hill but with just a wiff of the right peddle it pulls no worries....everyone thats driven it comments that its very torquey....its running a NA six port with a wolf 3D...we are running four ports open down in the low end and the two extra ports open up in the rev range using a powervalve servo motor off an RGV250 motorbike....oh by the way....its not a two stroke....however i still think two strokes are far better than fourstrokes anyway We are also flying the twostroke flag at work by converting numerous CRF450s/CRF250 motorcross bikes to CR500 twostroke powered machines

[Tony de Wonderful]

Can you get diesel rotaries?

[VB-]

SK, why does one 'cycle' mean that all 3 faces of the rotor have to see combustion pressure? why isnt one revolution of the output shaft one 'cycle'? you have intake compression combustion and exhaust all happening per revolution of the ecentric shaft, all be it on seperate sides of the rotor... i think this is one of those things that looks good on papare, having the whole 4-part cycle carried out in a single **cylender** in just one revolution of the crank.

*** (cant remember what that stupid epictroid thing is actually called lol)

2 vs 4 stoke i cant see, i see how it is a 2 stroke, shit it has ports instead of valves for a start, but at the same time, it does have seperate 'chamers' for each part of the cycle, much like a 4 stroke doesnt it? although it has only 3 chambers for 4 parts of the cycle, hence i cant decide. 3 stroke motor????

going off my first thought, if one cycle is only one revolution of the eccentric shaft, then that would mean it is really only a 1.3 litre also, as it only moves 1.3 litres of air per 'revolution'. i just think they are a nugget of a 1.3, not an average 3.9 2 stroke.

that said i'm not an engineer in anyway. am i just buying into mazda's lies?

[Streeter]

they are different, arguing over what they equal is the same as arguing about terminology.

where do you count revs? *thought this was from the crank/eccentric shaft? the cams in a piston engine go half speed, why dont we count them as engine speed?

how do you classify displacement? *I always thought it was supposed to be combustion chamber, arguably a combustion chamber needs spark plugs, only one side of the rotor has plugs at any one time and that is what they run with. Misleading? maybe, but saying its 2 or 3 times the size is just as bad.

but basically comparing them by volumetric size or revs is retarded.

They arent popular cause they arent as fuel efficient as a piston motor, for a daily commuter that is the end of them.

For a sports engine they are a proven contender, very low centre of gravity, make good enough power no matter how you want to count the revs or size. And ultimately fast enough to cop the ban hammer at lemans. That has to say something about how good they can be?

one thing Ive read here a couple of times is the two plug deal... Vlad from Victoria ran 8seconds and always pulled the trailing plug leads off. So there goes that theory of needs the extra spark for power, thats simply incorrect.

My hate I have with them is that they are too fragile. Most piston motors can knock a little before they give up. Rotors seem to be missing and stuffed before you even know what happened, rebuilds are expensive and a pain in the arse. I enjoyed the time I had playing with them for 6 years and have a soft spot for them. But Ive had enough with maintenance and tinkering and just want to drive... so I swapped to piston motors.

[Roy]

I thought the 20B Cosmo had more torque std then an RB26!

[JAS-25T]

The only thing you can compare between piston and rotary is combustions per rotation of output shaft.

And for that, the rotor does one (for each rotor)

piston does half as many as there are pistons.

end of story.

[ylwgtr2]

yep....you dont need the trailing plug....just wondering....can we fit a set of rb26 cams to them?

[mad082]

i disagree with the 2 stroke thing (not saying that are a 4 stroke either). i see them as a single stroke because at no point does the rotor become stationary like a piston.

also while i can see the 3:1 shaft difference, and engine difference, you still can't really compare the 2. they are 2 different things that do the same job in 2 different ways. the wankel makes good power for what it is. you can go on about how it is "like" a 3.9L 2 stroke 6 cylinder, but realistically they are nothing alike.

something you also have to take into account is the differences in leverage of the cumbustion forces on the 2 types of engines.

also the examples sydneykid used of the f1 car and indy car, etc are probably the most pointless examples i have seen. sure, lets compare an engine that probably costs millions of dollars to build to an engine someone has built on a much smaller budget.

at the end of the day, it is horses for courses. the debate is going to go on forever, just like the fwd/rwd debate as well as the v6 vs the straight 6 debate. in the next decade or so it will be a debate between petrol engines vs diesel vs electric. people are always going to find something to debate over.

[Birds]

they are different, arguing over what they equal is the same as arguing about terminology.

where do you count revs? *thought this was from the crank/eccentric shaft? the cams in a piston engine go half speed, why dont we count them as engine speed?

how do you classify displacement? *I always thought it was supposed to be combustion chamber, arguably a combustion chamber needs spark plugs, only one side of the rotor has plugs at any one time and that is what they run with. Misleading? maybe, but saying its 2 or 3 times the size is just as bad.

but basically comparing them by volumetric size or revs is retarded.

They arent popular cause they arent as fuel efficient as a piston motor, for a daily commuter that is the end of them.

For a sports engine they are a proven contender, very low centre of gravity, make good enough power no matter how you want to count the revs or size. And ultimately fast enough to cop the ban hammer at lemans. That has to say something about how good they can be?

one thing Ive read here a couple of times is the two plug deal... Vlad from Victoria ran 8seconds and always pulled the trailing plug leads off. So there goes that theory of needs the extra spark for power, thats simply incorrect.

My hate I have with them is that they are too fragile. Most piston motors can knock a little before they give up. Rotors seem to be missing and stuffed before you even know what happened, rebuilds are expensive and a pain in the arse. I enjoyed the time I had playing with them for 6 years and have a soft spot for them. But Ive had enough with maintenance and tinkering and just want to drive... so I swapped to piston motors.

Agree 110%! This man knows EXACTLY what he is talking about and everyone reading this thread should be taking note. Comparing rotaries to piston engine design and basing this comparison on the design of the piston engine is f***ing stupid. It's like comparing a horse to a bird...they both go fast, but where do you start with a fair comparison between them? One uses legs, one uses wings. Sounds f***ing ridiculous but that really is an accurate analogy of what people are saying in here.

It's just mind boggling...people stating that a piston engine has more clever engineering because some of the parts in one engine move faster than some in another? When the parts and physics of it are completely different? Have these people even seen how a rotary works? As I said before, the only thing these engines share in common worth comparing is an output shaft leading to a gearbox. Even then, waste of time, because both engines were designed for different applications. Decide if you like or dislike rotaries, but don't go saying ridiculous shit like one engine revs better than the other and one of them cheats! Mechanical engineers would laugh at you!

[CatsEyes]

well the fact that people have used rotaries in aircraft means that they can't be that unreliable

personally i hate the sound of a NA rotary. don't mind the sound of a turbo one on song though.

The rotary engine in early aircraft was a different animal altogether!

It was an early and inefficient type of cylinder-based aero-engine, from the WW1 era, which became obsolete because of a lack of torque.

http://en.wikipedia.org/wiki/Rotary_engine

I suspect you're thinking of the similar-looking RADIAL engines in piston-engined aircraft from the 1930s onwards. They WERE successful and reliable. But 'radial' = the arrangement of the cylinders, and had nothing to do with rotors.

[adamskill]

Is it just... a lack of popularity? Technology? What's holding the ol' Wankel engine from really competing?

hey mate, i dont wana piss on your paraide, but have u been to the drag races rescently?? easily 75% of the cars involved run rotary engines. the last few times i have been to willowbank it has been absolutley dominated by rotary powered cars, from mazdas to nissans, fords, and even a mitsu. and as for competing, they blow most of the competion away!