Why Do Rotaries Suck?

[GT-R32]

Aw dont give up! We are so close to a conclusion. Why cant we measure the cpm speed by the e/shaft?

We aren't close to anything.

However I would hope that by now everyone in this thread has got their head around how a (Mazda) Wankel operates and how it turns its combustion into power in a car. They can then make their own assessment of whatever people have said.

[Parag0n]

And if you get a 1L or 1.2L version they can run 9's out of the factory with next to no modification. Where's the rotary that can do that?

So this "Rotatries run 6's" crap i just that, crap.

First off you've gone WAY off the plot trying to compare your meat torpedo bike to an automobile, don't do that, completely different category of vehicles.

That is why ANDRA sanction different classes of drag racing for different vehicles, Doorslammers, Top Fuel / Alcohol, Ozmod etc..

And I was simply stating in ANDRA Pro-Turbo drag racing the vehicles that are in the 6 second bracket currently are either POWERED by a Rotary or a 2JZ.

(PAC Racing now has the fastest rotary in the world over the quarter mile

)

Sorry to dissapoint you regarding the RB series engine but it's a long way off a 200mph+ trap speed 6 second ET.

I'm not saying that an RB series motor is not capable of a 6 second pass, but at the current rate the workshops who are using RB motors in drag racing are hardly close, the difference between a mid 7 and a mid to high 6 / 200mph trap speed equate to hundreds of thousands of dollars in drag racing.

Edited September 29, 2009 by Parag0n

[jase-r34]

^^ Agreed. There has been enough argument from every side with plenty of info provided for everyone to make their own conclusions.

Edit - Was agreeing with GT-R32.....

Firstly LOL at the bike hater. Is that because they aren't rotary powered? Or cause it's faster than the RX7......

I don't doubt what your saying is true Paragon. But it was never my argument that different categories should be raced against each other. IMO rotaries are in a different category to Piston engines yet they compete against each other don't they? Just because they are both in cars doesn't make them the same.

And I don't really give a shit if a 2J is running 6's in whatever and a RB26 is doing 7's in a 32, since this thread is not about extremely modified dragsters anyway. We were talking about principles and operation of rotaries vs pistons. I used stock road going versions of both and got flamed for it.

If Mazda can lie about capacity and everything else, then I can compare a bike to a car to prove a point

[Parag0n]

Anyway I think a mod should close this topic it's been done to the death and even though you've probably read some insightful comments regarding the NSU Wankel it'd probably be wise to lock it before it degrades into a Boostcruising like shitfight.

[jase-r34]

LOL. Now that I do pretty much agree with.

[ylwgtr2]

Firstly LOL at the bike hater. Is that because they aren't rotary powered? Or cause it's faster than the RX7......

hahaha bike hater????I run a motorcycle smash shop dude....i personally own about 10 motorcycles and have raced since i was about 8 ....i must really hate them

Edited September 29, 2009 by ylwgtr2

[jase-r34]

hahaha bike hater????I run a motorcycle smash shop dude....i personally own about 10 motorcycles and have raced since i was about 8 ....i must really hate them

LOL. I wasn't talking to you.

[scathing]

just out of interest....whats sort of 1/4 mile times do guys running honda engines do?

Since apparently the engine is all that's important for quarter mile times, the fastest dead stock Honda engined road legal production car would be the Ariel Atom. The current one does a 10.6s pass (I assume its the supercharged version).

[ylwgtr2]

oh ok....i just saw the edit in your post....

[ylwgtr2]

Since apparently the engine is all that's important for quarter mile times, the fastest dead stock Honda engined road legal production car would be the Ariel Atom. The current one does a 10.6s pass (I assume its the supercharged version).

im confused.......who said that?

[Smity42]

You can and in fact Mazda does. But is it correct to state that "a rotary engine does 9,000 rpm"? You will say, "well of course it is correct because the eccentric shaft does 9,000 rpm". Whereas I will say "no it isn't correct because the rotors are only doing 3,000 rpm". When we say "an engine does 9,000 rpm" the natural assumption is that all of the engine is doing 9,000 rpm". Now in a 2 stroke piston engine that is 100% correct, all of the engine is in fact doing 9,000 rpm. But in a rotary engine only the eccentric shaft is doing 9,000 rpm, nothing else. The rotors are only doing 3,000 rpm.

Keeping the above in mind, that means 100% of a 2 stroke piston engine is doing 9,000 rpm, but only 33% of a rotary engine is doing 9,000 rpm. In other words the vast majority of a rotary engine (ie; 67%) is only doing 3,000 rpm. So when someone says "a rotary engine does 9,000 rpm" I say rubbish because the whole engine is not doing 9,000 rpm. In fact I say double rubbish, because most of the engijne is only doing 3,000 rpm.

But wait! Rotary engines ARE a 2 stroke:

That’s because they are a 3.9 litre 2 stroke.

Sorry, Couldn't help myself .

Yes i did notice that you clarified with '2 stroke piston engine' everywhere. However, by definition a 2 stroke is a piston engine, but thats an argument you are not going to come round to, so I am not going to bother arguing it again. I am however still waiting for a definition of a 2 stroke you can point me to that you can make a rotary fit in to.

Oh come on, a 13B rotary combusts/fires 6 times in one complete cycle of it's rotors, irrefutable fact. Whereas a piston 4 stroke 6 cylinder would only combust/fire 3 times in one complete cycle of it's pistons. So it produces double the power of a 4 stroke because it has double the number of combustion process in one cysle, ineficiencies notwithstanding.

Cheers

Gary

Edit: I just realised why i balls'd up that comparison. I still disagree though:

What you actually need to look at is crank rotations.

For a 4 stroke - one complete combustion cycle of a piston rotates the crank 720 degrees

For a 2 stroke - one complete combustion cycle of a piston rotates the crank 360 degrees

So if we rotate the crank the same amount, the 2 stroke fires twice as much, so we double its capacity comparing it to a 4 stroke.

For a Wankel - one complete combustion cycle of a rotor rotates the eccentric 1080 degrees, so to compare it to a 4 stroke we multiply by 720/1080 or 2/3.

I suppose sydneykid is going to comeback now with his 3:1 ratio argument. I don't have an answer for that other than to agree to disagree.

The only other argument you could put forward for doubling a 2 stroke capacity is because when we normally measure capacity we only count one half of the combustion process (the 'top' half of the piston), so we need to double it to count the other half (the 'bottom' of the piston). but this also does not apply to a rotary as we have already counted all 3 faces in obtaining our 3.9L figure.

Edited September 29, 2009 by Smity42

[ylwgtr2]

no one has answered my twostroke loss of stroke question yet ......im waiting.....and if we measure an engine(two stroke) on the amount it pumps are we doing this through the plug hole or out the exhaust port?

Edited September 29, 2009 by ylwgtr2

[jase-r34]

Where are the RB engines? They're not going to be in the 6's anytime soon, meanwhile Puerto Ricans get 13B's to run 6 second quarters.

He said it. Apparently a Puerto Rican holding a 13b can run a 1/4 mile in 6 seconds.

[jase-r34]

But wait! Rotary engines ARE a 2 stroke:

Sorry, Couldn't help myself .

Yes i did notice that you clarified with '2 stroke piston engine' everywhere. However, by definition a 2 stroke is a piston engine, but thats an argument you are not going to come round to, so I am not going to bother arguing it again. I am however still waiting for a definition of a 2 stroke you can point me to that you can make a rotary fit in to.

What if the 4 stroke was a 3.9L V12? It would fire 6 times then. The number of 'combustion mediums' is not relevant. Otherwise you would have to double a 3.9L V12 when comparing it to a 3.9L 6 cylinder wouldn't you???? In one complete cycle one has fired 6 times and the other has only fired 3? But we don't do that.

What you actually need to look at is crank rotations.

For a 4 stroke - one complete combustion cycle of a piston rotates the crank 720 degrees

For a 2 stroke - one complete combustion cycle of a piston rotates the crank 360 degrees

So if we rotate the crank the same amount, the 2 stroke fires twice as much, so we double its capacity comparing it to a 4 stroke.

For a wankerl - one complete combustion cycle of a rotor rotates the eccentric 1080 degrees, so to compare it to a 4 stroke we multiply by 720/1080 or 2/3.

The only other argument you could put forward for doubling a 2 stroke capacity is because when we normally measure capacity we only count one half of the combustion process (the 'top' half of the piston), so we need to double it to count the other half (the 'bottom' of the piston). but this also does not apply to a rotary as we have already counted all 3 faces in obtaining our 3.9L figure.

Mate, a lot of that makes perfect sense to me and helped me figure out a few things I was still trying to get my head around. Good post!

[Smity42]

Yeah i actually stuffed it up in my V12 vs 6 comparison - it would still only be half the measured capacity that has fired. The rest is still relevant but - see edited version

Edited September 29, 2009 by Smity42

[jame88]

I'm sorry if I come across as flaming you, it's not intentional I can assure you Perhaps you need to go back to the start of this thread and follow the flavour. From the start I put forward an opinion and supported it with facts. A few guys tried to convince me that I was wrong, but they failed. Some guys completely misunderstood what I was saying and took it as a biased rotary attack. So they popped over to the rotary forum and got one of the big guns over to have a go. He resorted to the personal insults when he couldn't support his stance as well as I could mine and then eventually he agreed with me and left.

Ok i appreciate you saying that. I have however read through this whole thread, thats why i decided to post.

For those of you who still doubt what i'm trying to say, have a look at this youtube vid:

This video explains it well, and is much easier than trying to explain with words in a post.

Does anyone still think there is a step up gear ratio between the rotors and eccentric shaft?

The stationary gear pinion and the ring gear on the rotor keep the rotor where it should be for the Wankel cycle, much like the cylinder bore keeps a piston where it should be. A Wankel needs this 3:1 (no other) ratio to operate properly just as a piston engine needs a bore.

[~rx3~]

Hang on, so the outside of the rotor does 3,000 rpm but the inside does 9,000 rpm, That's a good trick, but I some how doubt it. The fact is the whole rotor is doing 3,000 rpm, and the rotor is the combustion medium, it's what makes the power, somewhat like a piston in a piston engine in that regard. So comparing it to a water pump is pretty stupid, they don't produce any power. Nice try on muddying the water with the camshaft rpm, but that's a 4 stroke. How about we compare it with a 2 stroke piston engine with no valves (like a rotary) and no camshafts (also like a rotary). Bingo, everything is doing 9,000 rpm (or cpm if you prefer) but in a rotary, oops the main parts, the bits that make the power, the rotors, are only doing 3,000 rpm (or opm if you prefer).

Why do I feel like I have answered this all before? Maybe because I have.

The simple truth is what the eccentric shaft lobes do is to convert the 2 styles of kinetic energy of a rotor, the rotate and the orbit, into one style of kynetic energy, the round and round rotation of the eccentric shaft itself. There is no magic here, it's much like the the throw of a crankshaft converts the up and the down of a piston into the round and round rotation of the crankshaft itself.

Cheers

Gary

http://www.rotaryengineillustrated.com/how...netary-m-2.html

it is magic ,the rotor orbits the shaft at 9000 orbits per minute while it rotates at 3000 rpm.

[~rx3~]

I'm not here to win anything

Cheers

Gary

[~rx3~]

won that one already.

Cheers

Gary

[~rx3~]

. How about we compare it with a 2 stroke piston engine with no valves (like a rotary) and no camshafts (also like a rotary). Bingo, everything is doing 9,000 rpm (or cpm if you prefer) but in a rotary, oops the main parts, the bits that make the power, the rotors, are only doing 3,000 rpm (or opm if you prefer).

Cheers

Gary

dont the pistons do 2 strokes or cycles for one turn of the crank? 1 turn of the crank = 1stroke down + 1 stroke up . and only at 90 and 270 degrees are they doing the same speed as the crank, at 0 and 180 they are stopped .if the strtoke is 100mm the part of the crank that the piston is attached to travels 314 mm and the piston travels 200mm .please correct me if im wrong