Is a 13B really a 2.6 liter????
 

I read a article in sport compact car today that pissed me off! They say the 13B is really a 2.6, and the 3 rotor is really a 3.9!! He said Mazda has been lying to us all!?!
This is BULLCRAP!!! I'll state my thoughts quickly and see what everyone else feels. He states the rotary should be doubled because it fires twice as often as a piston engine. If this is true, why dont we Double the displacement on a 2 stroke piston engine? And a single rotor fires 3 times, yes 3 times in 2 crank rotations. Not 2. So going by his rules, I guess we should TRIPPLE the size! Articles like this is why the rotary has a hard time with the public. Write your responses, and reasons, maybe we should all write to Sport Compact Car!!

SAE says it's a 1.3L, so that pretty much sets the international standard. What certain authors and racing organizations want to call the 13B is up to them.

What is the SAE?

Re: Is a 13B really a 2.6 liter????
 

well we all know it's not the size that counts. but how many times you use it :D

but what does the size of something have to do with how many times it's used...:confused:

umm... it fires once per rpm. and a piston fires every 2nd rpm. so it fires twice as often.

The guy from Sport Compact Car is wrong. The 13-B is a 1308 cc engine producing the same number of power impulses per SHAFT revolution as a 4-cylinder piston engine. What confuses many of these guys is that for each complete revolution of a ROTOR, there are three power impulses. Multiply that by 2 rotors in a 13-B and you get six power impulses per rotor revolution. But since the eccentric shaft does three revolutions for each complete revolution of the rotors, you have to divide these six impulses by three, which gives you two power pulses per rev. Each compression cycle displaces 654 cc's. Two rotors means that this figure is doubled to give you 1308cc's. The real difference, besides less mechanical stress due to rotary motion vs. reciprocating, is the DURATION of the power stroke. In a piston engine, the power stroke lasts thru 180 degrees of crankshaft rotation as the piston is forced from top dead center to BDC. This represents 1/4 of the entire cycle. In the rotary, the power "stroke" lasts thru 270 degrees of shaft rotation, which is about 1/2.66666 of the cycle. Therefore, the longer power sequence = more useable power produced from less cubic inches. Also consider that no power is required to drive a valve train and it's not hard to figure out why this very low-displacement engine can perform so well. I saw a sign on back of a Lambourgini Countach at an auto show that said," The only replacement for displacement is technology." Nowhere is this more true than with the rotary.

Re: Is a 13B really a 2.6 liter????
 

When attempting to get a reasonably accurate comparison to piston engines, the capacity of rotaries has often been doubled. This is mostly done by automotive magazines, because their job is to compare cars. Did he really say "Madza lied" or did you exagerate that just a bit...? It does! But more important is that each rotor inhales it's swept capacity (654cc for a 13B) once per crankshaft revolution, whereas a 4-stroke piston does this only once every second revolution. So assuming both engines have 100% volumetric efficiency, a 1308cc 13B sucks in twice as much air as a 1308cc piston engine at the same rpm, or the same amount as a 2616cc piston engine. Airflow equals power, so airflow is a good way to compare engines.
Rotaries actually have a slightly lower VE than piston engines, which is why nearly all motorsport formulas use an equivalency ratio of 1.8 instead of 2. So a 1308cc 13B competes as a 2354cc engine. A 1962cc 20B might be quoted in magazines as being 3924cc, but will compete as 3532cc. You can if you want, no-one's stopping you... ;) Ah, no it doesn't. A single rotor fires once per crank rotation, but the rotor is only spinning at 1/3 crank speed. A twin rotor fires twice per rev just like a 4-stroke 4-cyl. No they're not. The writer may not have been completely correct, but he was less incorrect than you! I think you're just getting a bit too emotional over such a trivial issue. Lighten up and enjoy your engine. ;)

I think he's just saying that all of this confusion about the rotary is why people have such bad opinions about them. I'm sure all of us have heard the classic "you have to rebuild those every 50k right?". And, of course, whenever anyone hears that my car has the displacement of a metro, they instantly assume that it's slow.

ha, kill the 1.3L Metro motor, long live the Rotary!!!

Nice job blowing that article out of proportion. He says that the rotary is 1.3L if you prefer tradition over logic, and that the rotary is most easily comparable to a 2.6L engine.

Isnt it 2.6L in total Volume?

I have been lookign up this info, and I think it was Delta Rotary, that said while one chaber is at 100% (654cc), the otehr 2 are at 2/3 and 1/3 the size per rotor. And since Mazda and others measure it by 654cc per rotor, the other 2 chambers on each rotor were left out of the equation.

This entire size thign is alwasy beign debated.

There are a couple of post about this.

I have heard this argument a thousand times. Thanks to those of you who made sense of it. I love to tell the guys with 5.0 Mustangs that I just kicked their butts with 1.3 liters

Sig :)

photoresistor ;

SAE = society of automotive engineers.

thanks PPC

heh, ive heard countless times that they instantaneously just emplode @ 50k and can never EVER be rebuilt ;)

That's funny, b/c I was talking to one of my friends from school, and he said that his dad said the same thing. Once they blow, they are gone, and they can't be rebuilt. I told him to look under my hood since I had a reman. with less than 2000 miles at the time.

Its all about the HE/SAID SHE/SAID BULLSHIT!!! lol

Can I start a Mac vs. PC war now?

It just seems appropriate. ;)

Macs rule, Pc's suck- bottomline!!:bigthumb:

Who told you this? And how did they talk you into the idea that "longer power sequence" equals "more usable power"? In short, where does this kind of crap come from? "Usable power" has nothing to do with what portion of a rev is occupied by the expansion phase, UNLESS you consider that the longer the hot gas spends in expansion, the MORE pressure is lost due to heat soaking (from gas to metal) of the combustion chamber. If you consider this, you'll be starting to see why a wankel engine has lower volumetric efficiency than a piston engine...

At least you got that part right. No power is required to drive a valve train in the wankel. Since the advent of ball bearings, though, valve train power hasn't been the biggest of worries in the piston engine world.

As has been amply demonstrated in this thread, the Mazda rotary isn't exactly a "low displacement" engine. Unless you consider 2.6L low displacement, of course.

Oh, and "Zach McAfee", your use of the word "efficient" in your sig seems to imply that you think the Mazda rotary is "efficient". Well, it ain't, except in a power-to-WEIGHT sense. In a power-to-FUEL-BURNED sense, it's a major pig, as I'm sure you're aware, since you (I hope) are the one paying to keep your car fed.

And yes, I drive a '94 MB Touring. Do I care about gas mileage? Not one little bit.

Re: Re: Is a 13B really a 2.6 liter????
 

[/list]I have to say safely that your not fully right about that!
Alright, my Dad and I run a Mazda shop, I've been watching him rebuild rotary's since I was 8 years old. Sometime about 2 years ago I took the parts from a real rotary, put together a simple model of a single rotor. (one side housing w/ stationary gear, one rotor, the eccentic shaft, and a aluminum housing. Having five Of my friends come into the shop, ( they didnt believe me ) I connected a big breaker bar to the end of the eccentric shaft. Watching closely and all of us counting the amount of fires in the camber, a rotary fires 3 times, in 2 rotations!! I know rotarys Very well, and if you actually took the time yourself to do a mach-up with a real rotary and not a diagram in a book, you'll see I'm right on this. You are right, a rotary fires once in one crank revolution. But what your missing is its half way to another power stroke. So technically it fires 1.5 times per rev. But since you cannot do that, the only way for a rotary to complete its full firing order, it has to rotate 720 degree or two crank rotations. This is FACT, I saw it myself! So a two rotor will fire 6 times in a 2 rotation period, which puts its firing order in the area of a 6 clyinder, which also fires 6 times in two revs. Well, that about does it, sorry for getting "emotional" about rotarys, didnt mean to sound like a baby, and yes I do enjoy my motor, just I want the public to understand a rotary, and in that article, it does say Mazda Lied. What are new people to this motor going to think? Now the engine seems enefficent when doubled, and I dont think its right. I apologize if I started anything bad on this thread, I didnt intend too.

I mean really, who throws a shoe!
 

Well guys, I am currently studying automotive technology, and the way that they measure displacement is the total volume of one combustion chamber from top to botom dead center usually using the cylindar diameter. now, since the displacement for one rotor from top to bottom dead center is 654cc and there is two of them, that would equal just over 1300 cc. they don't take into account that there are more than one rotor face. it is all about crankshaft rotation and not even necessarily about the number of combustions per revolution either, because a four cylindar will produce the same number of combustions per rotation as a rotory total. that is what the SAE goes by. simple and easy. get it hahahaha:p:

displacemnt is pie over 4 x bore squared x stroke squared on a boinker motor if i remember correctly.

Re: Re: Re: Is a 13B really a 2.6 liter????
 

I think you're using the word "fire" a bit loosly. We're refering to the number of times the spark plugs are fired (i.e. the number of power pulses) per crank rev. Each rotor fires once per rev. The number of "fires" in the engine at one time is irrelevant, particularly since I think you're counting the exhaust stroke in your "fire". You're right, I've seen lots of diagrams in books. I've also got about a dozen different animations on my computer. I also helped build a working exposed rotary from half of a 12A, and stood on club displays and explained it to people who'd never seen the internals of a rotary before. I've seen dozens of disassembled rotaries over the years, and finally there's a housing and rotor sitting next to me on my desk! Don't worry, I know the internal workings of the rotary well. So now you agree? No! You've just said a rotary (one rotor) fires once in one crank revolution, so a two-rotor fires twice per rev, just like a 4-cyl. Go to Rotary Engine Illustrated and download the excellent animations from there. They'll show you this clear as day.

If you really want to melt your brain, see the thread in
LOUNGE under a similar heading. I was almost convinced of the 2616 displacement idea, but it's impossible to directly compare a rotary with a piston engine due to the longer duration of the cycle phases in the rotary.

I think I may be a idiot
 

Hey guys I am TRULY sorry!! I escpecially want to apologize to NZConvertible, hey you were totally right, I was totally wrong. Today I went over to the shop and after talking to my dad, (and him telling me I didnt count right) I realize I started count on a power stroke, when in practice you should always start on a intake cycle, and my dad told me I was doing it the wrong way, and the reson for the extra power pulse. I feel like a HUGE DUMB-ass. A rotary fires once per rev. And a 2 rotor fires twice per rev. Honest mistake, I feel like the biggest begginer now :( . Now if you all excuse me, I'm going to go outside and hit myself in the head with a big 13b rotor.

2600cc?????
 

I forgot to put that you combine the number of combustion chambers. you have to take the combustion chamber(s) at bottom dead center, take the total volume of each one and then combine the number of combustion chambers. I think that might be a little easier to understand.(mabe)
Being that there is only one face of the rotor at botom dead center per rotation, per rotor. the total combined displacement would be 1308cc, would it not:)

I know what your saying. I didn't think anyone would get what I said confused because its just a play on numbers.
I didn't mean Nth = 1 - Tlow/Thigh kind of efficiency.
I meant horsepower per liter.
My $150 a month gas bill by no means makes me feel like I drive a fuel efficient car.
Blah.

Ok, now this is starting to bug me. What makes things like this come out of peoples' mouths? Did I miss an issue of "Automotive Disinfo Monthly"?

Since you're another one who obviously didn't miss that issue, why don't you tell me? Disregarding for a moment that it's arguable whether they really are longer, WHAT do the "longer duration of the cycle phases" have to do with ANYTHING regarding power, efficiency, torque, or square miles per pitchfork, and WHY?

Funny, the rotary engine causes so much confusion for people. But we on the forum know the truth and the facts. The 13b 2 rotary engine, is a 1.3 liter engine.

Re: Is a 13B really a 2.6 liter????
 

Well this will really piss you off. The 2 rotor is actually 3.9litre and the 3 rotor is a wopping 5.85 litre.

http://www.mikesdriveway.com/misc/rotor.doc

Before replying have a look at every post in this thread. Without exception everyone refers the crankshaft as a reference, eg "The rotary sucks 1.3litres per crank revolution". No-one has stopped to ask if using the crankshaft as a reference is valid.

i'll put this in very simple terms, the 13b is a 1.3 liter engine but consumes like a 2.6 therefore ppl like to call it a 2.6, but technicaly its not

agreed about that 2.6 L consumption

this should be in the lounge

Re: Is a 13B really a 2.6 liter????
 

The truth is that it's a 1.3 liter. That aside, its corrected displacement is 2600cc, or 2.6L. You only use 2.6L for heavy-duty track events, and it doesn't hold true in the real world. It's kinda like how in SCCA rally, adding a turbocharger is like effectively increasing your displacement. The same goes for rotaries, and because they're basically a two-stroke engine, they get their actual displacement DOUBLED to account for the advantage in power production. So, SCC is both right AND wrong.

the SAE calls it 1.3 liters. That's all I care about. You can argue about it all you want but the guys who make the rules say it's 1.3.

And guess what my Belgian car owner paper says?

2600cc.

go figger

Do you have a paper number?

Re: Re: Is a 13B really a 2.6 liter????
 

The rotary is not a 2 stroke. It is a 4 stroke just like the majority of automotive piston engines today.

Then you're missing the point just a bit. Why do you think we measure and quote engine capacity? Mostly it's because we want to compare different engines to each other. When you're comparing similar engines (i.e. pistons) this is easy, but when compary two very different engine (rotary and piston) you need to have some meaningful way to do that. It doesn't take a rocket scientist to realise a "1.3L" rotary is not even close to a 1.3L piston engine in practically any measurement.

The two places where you most often hear rotaries quoted with double their displacement (i.e. 2.6L 13B) is in car magazines and motorsport formulas. And why is that? Because both exist to compare cars to one another in some way.
The SAE only say it displaces 1.3L, which it does. The SAE does not say "a 1.3L rotary is just like a 1.3L piston engine".

The FSM states that the displacement of each rotor combustion chamber is 654 c.c. Doubling that for two rotors gives you 1304 c.c., hence the "13" in 13B.

The displacement is not 2.6 liters. It's just that in the hopeless attempt to compare rotors and pistons like apples and oranges, idiots think it is fair to double the displacement because there are more power strokes per rpm in a rotary. I can't believe the mag people still don't have it right.

The capacity of one *chamber* is 654cc, not one rotor. Even mazda say this.

There are 6 chambers of 654cc, so that's 3.9 litres.

BTW, rotary and piston motors are actually very similar. Most people fail to see the similarities because they a looking at the differences. If you take one chamber and follow it through it's cycle it does everything exactly the same as a chamber in a piston motor except that it expands over 270* instead of 180*. The chamber goes through inlet, compression, combustion and exhaust just like a piston motor. The volume of the chamber follows a sine wave just like a piston motor. Have a look at the engine comparison here, the rotary does everything the same as the piston motor just the output shaft spins 1.5 times as many revs.

http://www.mikesdriveway.com/misc/rotor.doc

MikeC:

You're some mad professor who is confusing the point.

There is one combustion chamber for each rotor, just like there is one intake port, one exhaust port, one TDC, etc., for each rotor.

You misread or misunderstood me, or both. I said:

"the displacement of each rotor combustion chamber is 654 c.c.". This is correct. Read the FSM. I will side the the Mazda engineers on this one.

You are suggesting there are six combustion chambers in a 13B. Are you out of your skull? :scratch:

Not at all. If you read any technical document such as stuff by Kenichi Yamamoto, Richard Ansdale or Jan Norbye without fail they always talk about the three chambers around the rotor. They are three independant chambers just like three pistons that happen to fire in the same location. Start by following a single chamber through it's cycle. It goes through inlet, compression, combustion and exhaust. The other chambers are doing the same thing in the same way that other pistons in a piston motor are.

BTW, I'll take that mad professor comment as a compliment :)

Re: Is a 13B really a 2.6 liter????
 

Does anyone have a link to this article. I've search the Sport Compact Car website quite a bit with no luck and I don't think we get this mag in Australia.

well in theory hes correct, but that doesnt change the actual engine size, which is still 1.3 litres, if u wanna get that spedific u could say that the engine also revs higher bla bla bla etc

actual engine size is still 1.3L ..... is your apparent statement of fact here based on blind faith in mazda's rating, or rational thought?

Hi Kevin,

Here's another way of looking at it. (I'll repeat some of what I've said before for the benefit of anyone who didn't read the other thread).

The most popular method of measuring the capacity of the rotary is to take the amount of air inducted over 2 revs, which is 2.6 litres. This gives the correct capacity for the piston motor but I don't think it does for the rotary. The reason is you can take the drive off the engine in a different way and get a different result for the same engine.

For example you could take the drive off the camshaft of a 4 stroke piston engine so that the output shaft effectively spun at half the speed. If you then spun the output shaft through 2 revs and measured the volume of air inducted you would get twice what the engine really is because it has really spun through 4 revs. So a 2 litre engine would induct 4 litres of air. The way to get the true capacity is the take the air inducted, multiply by the number of degrees the output shaft turns for a single chamber to expand and divide by 180. So you get

Capacity = Air over 2 revs * degrees for expansion / 180

For this engine a single chamber will expand over only 90* because the engine is going twice as fast as the output shaft. So the capacity is 4 litres x 90 / 180 = 2 litres. So no matter how you take the drive off the engine you get the correct capacity.

If you then take a 2 litre engine and take the drive off the crank in the normal way you get 2 litres * 180 / 180 = 2 litres. So for a normal piston engine you still get the correct capacity.

Now ... for the rotary the air inducted over 2 revs is 2.6 litres and the degree of crank rotation for expansion is 270 degrees. So 2.6 * 270 / 180 = 3.9 litres.