I have been thinking, isnt the 13B more comparable to a 2.6L, because the rotors fire once per revolution compared to once every 2 revolutions on a piston engine??

 

It's the biggest debate plaguing the the piston engine owners since the inception of the rotary engine. Who cares!?

Our engine's mechanic's is so completely different than the piston engine that mere displacement of the rotor housing or their firing order can't define comparability to anything else!

 

do you know what displacement is??????????

now follow the defination of displacement and see what you get?

*gasp* 1.3

 

or for me, here shortly, 2.0




hopefully this time

 

The displacement is 1.3L. Or to be exact, 654x2 cc.

The displacement equivalent is 2.6L. Or, 654x4 cc.

Among others, the displacement equivalent number is used by racing organizations (e.g. FIA, USAC), Ford, Daimler-Benz, and General Motors.

Total displacement is another measure. The displacement of an engine can be measured by following all of its elements through their motions until they physically begin to repeat themselves. The number of full cycles carried out during this process would be counted to arrive at total displacement. Therefore, the 13B would have a total displacement of 3.9L, as NSU would of calculated.

 

You're exactly right, 2.6 compared to the measurements by other manufacturers.

If we want to get technical though, Mazda measures their rotary engines correctly, and everyone else has their displacement doubled.

Either way, who cares

 

Alright so i was right i guess, thanks for clearing that up.

 

That's opinion. I think Total Displacement is a better measure. But, if you're talking strictly open space at one point in time, then yes, Mazda is correct.

NSU originally used total displacement because they believed it was the best way to measure it. However, they switched to the way Mazda currently does it after they realized that European taxes would cost more on a bigger engine.

 

I still say it's not our fault that rotaries are more efficient per ambient displacement than piston engines... If they built a piston engine that somehow miraculously fired twice per revolution, you think they would cornhole themselves by doubling the displacement figure? NO, they would call it what it was and brag about it being better than the next guy...

 

I wonder why people love to ponder over this so much. Outside of racing in groups that limit your displacement in a class or whatever I don't see why people have to make such a big deal about it. I don't think "there's no replacement for displacement" and I don't think big power from small displacement makes me incredibly badass. I just like the car and the engine yet some people go so psychotic over this....



I don't care if it's similar to a 2 stroke engine or whatever that argument about the sparkplug firing is or whatever. I think of it as 1.3L, and that's also nicer for the engine name being 13b... I don't run around going: "Yeah Mr Big V8 with 5 liters, I AM 1.3 YES HAHAA LOLOLOL I WINZZZ."

Oh well though. Only reason I came here was because it was the most recent post in this section...

 

There's a difference between making a big deal out of it and debating the issue.

 

I like the fact that it's 40ci x 2 and all the American muscle guys around here say size matters... Hmm that's interesting cuz my engine is 1/4th the size of their's.... lol I also like that fact that it sounds so much different than a piston engine. It's a beautiful thing.

 

over here it really doesn't matter, same in europe, it's like if you have a rotary you're in a different league, doesn't matter if it's a 20b or a 10a, you have a rotary, nothing more to be said

same with bikes and two strokes, they'll ask what size engine? all you say is two stroke and they'd be "oh...ok"

 

hehe, this debate will never end. however it goes, though. . . lets say the measurement is right as coming from mazda. thats nice. . . thats a lot of power from a 1.3ltr engine. okay, so, lets say its wrong and that the motor is larger. . . in the 2.6 (or whatever) area. well then. . . the power is about to par (i guess), but man. . . thats a nice SMALL package for the size.

 

https://www.rx7club.com/showthread.p...hreadid=269803

 

You dont call a 250cc two stroke motor bike a 500 cc just because it makes twice the power of a 4 stroke.

 

AGAIN...

Each of the 3 faces of that rotor effectively displace (if you dont know what it means, stop debating right now until you do) .65 liters. Mazda just did .65 x #rotors.

However, thats for one revoltion of the motor. To have every face of the rotor go through a complete cycle, the engine has to spin 3 times. For a 13B, that would make it a 3.9 liter motor that has to spin 3 times to go through its displacement.

However, its obviously not comparable to what the layperson would call a "3.9 liter engine" because obviously a 4 liter toyota v8 or a GM 3800 out class a 13b, which is because those engines go through their entire displacement every TWO revolutions.

Two revolutions of a 13b, at 100% VE, can suck in 2.6 liters of air. The reason the motor seems to rev high is that it uses its displacement in a different way than a piston engine, but is still fundamentally the same. Theyre both spark ignition, homogenous charge internal combustion engines.

But, however, because of hairbraned comparisons to piston motors by people who really dont know what is going on and dont understand the math and physics behind it make you people think that its a small displacement high revving high efficiency motor. Its not. The way they are, the reason theyre any good at all, is because they have a lot of displacement in a small area, because they're inefficient. theyre reliable because theyre really a 3.9 liter motor that needs another revolution to use the other third of its displacement.

Have any of you checked the thread I started in the race forum with the grown-ups? They cant get compression much over 9.5:1, thier BSFC is high and their BMEP is lower than comparable piston motors. Their large displacement and revving high without actually revving high because the e-shaft spins 3x for every one revolution of the rotor is how they seem to rev high and be small but still get the reliability of a larger motor spinning slower - its as if you had a 1.5:1 gear between the crank and transmission of a 4 stroke piston motor.

They are effectively 2.6 liter motors in a world that uses two revolutions of the output shaft as a benchmark. Theyre not two strokes, they operate nothing like them, and theyre not small (in displacement) or thermodynamically efficient. They ARE efficient with VE (with proper porting, and the proper paired header and intake manifold lenghts). Theyre not 'unfair', unless you try to bend the rules by going by the mazda rating for the displacement that really makes no sense. The people who run races and make the rules just banned them for not wanting to bother with angry rotards, basically.

But at any rate, a single rotor is no match for a 1300CC high rpm race-bike engine, nor is a 13B any match for a 2.6 liter full race piston motor. If you cant accept that and keep reacting emotionally, I suggest you find a therapist, because its a ******* motor.

 

On the same token however, if the eshaft has to make 3 revolutions per 3 fires, wouldn't that negate the fact that it's firing 3 times per revolution of the rotor?

 

Displacement is an arbitrary number used to show how much volume that is displaced in a combustion chamber. Displacement has nothing to do with the mass flow of the engine or displacement per revolution. 13b's are 1.3 liters of physical displacement, and 2.6 liters per revolution.

In addition, rotaries are much like 2 strokes, because more than one cycle occurs at once. 2 strokes have an intake cycle occuring during an exhaust cycle; however, there is no physical barrier between those 2 cycles, which is one reason why they are so fuel inefficient (they throw lots of fuel out the exhaust).

What matters is the displacement per revolution. VE can be calculated from that, comparing fuel efficiencies, power density, etc.

 

1.3 liters of physical displacement? How do you figure? what is your definition of "physical displacement"?

Displacement is a volume in 3 dimensions thats equal to a manifold defined by taking the flat area of something thats moving, and then the area of the 2d surface x how far it moves = the displacement. With a rotary its rotating in a more complex motion vs a very simple and easy to define as a cylinder by the piston head x how far the piston head works, but its still the same.

Trying to hide behind obfuscation to win an arguement doesnt work when someone actually understands whats going on, sorry.

Saying a rotary "fires" like a 2 stroke, as in ignition wise... who cares? It also has a tach signal just like a 4 stroke 4-cylinder and as far as how much air goes in and out its just like a somewhat inefficient 4 stroke piston engine with retarded spark timing with a very exhaust lobe on the cam and huge exhaust ports in the head. A renesis would be a lil more conventional with the side port exhaust. But thats beside the point.

Also, last I checked, there were 3 combustion chambers per rotor... and dont ever give teh displacement = combustion chamber size arguement, because then I could name a ton of 512cc small block v8s

The bottom line is it sucks in air at the same rate as a 2.6 liter piston motor, has the same tach signal as one (but it has more than one plug to fire and fires the second one twice because its got bath tubs for combustion chambers) but cant get the same compression ratios as a piston engine and is much less efficient - specific TORQUE (BMEP) is low and its BSFC is high. For those who dont know what they are I suggest you look them up so you know what is being talked about.

It doesnt act like a 1.3 liter 2 stroke either because it has intake compression power and exhaust discrete, isntead of doing exhaust and intake at roughly the same time and opening itself up (and exchanging air) immediately after the power stroke like a 2 stroke - for a rotary to really be a 2 stroke it would have to have spark plugs on the other flat side of the oval housing and another set of intake and exhaust ports and reed valves. THEN it would be effectively a 2 stroke, but it doesnt go through strokes, so thats irrelevant.

As far as volume of displacement vs the actual mass of air that goes in... I know that very well... but its the displacement that creates the actual vacuum for the air to flow into that actually sucks the air in, which is measureable, and a good way to rate motors. How well it fills that displaced area is the VE%, and no stock motor is at 100% VE that I know of, but thats beside the point completely.

They have no unfair advantages, but people who have some weird emotional attachment to them and the idea (care of marketing, I guess) that small displacement motors that rev high are "better" and are used to defeat the large displacement, domestic "enemy" sits well with you, so you try to argue that theyre small displacement to satisfy your own assumptions... and last i checked race rules and race classes use displacement to even the playing field, and its very unfair for a 1.3 liter piston enigne to be compared to a 13b that for all intents and purposes moves 2.6 liters of air, regardless of how ineficietnly it adds fuel to that air, burns it, and uses it to make power.

Personally, I dont give a ****, I want low buck in/high power out and really am completely ambivilant about what it takes to get there for street cars. For a race car in specific classes it can be cost effective but Im not making an ITA or ITS car, and until I do, Im not gonna mess with em.

 

There are 6 seperate rotor faces?

 

hmm i read that document posted on that other thread that was posted, and it cleared up pretty much every question i would want to ask about rotary displacement. my opinion is that they are too different to compare displacement-wise, and not really worth it.

 

So if you cant win you just leave?

With all this drama going on, is it any wonder so many race bodies have just said **** it?