GtoRx7

iTrader: (5)

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!!

Evil Aviator

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.

photoresistor

iTrader: (5)

What is the SAE?

Scott 89t2

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

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

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

Aviator 902S

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.

NZConvertible

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.

rotary>piston

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.

RX7_ZRO

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

BDoty311

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.

Anderson

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.

skyypilot

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

Zach McAfee

Sig

PPC-Racing

photoresistor ;

SAE = society of automotive engineers.

photoresistor

iTrader: (5)

thanks PPC

dr0x

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

Crionics

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.

DAN CARWIN

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

Sniper_X

Can I start a Mac vs. PC war now?

It just seems appropriate.

nashman69g

iTrader: (3)

Macs rule, Pc's suck- bottomline!!

Orange!FD

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.

GtoRx7

iTrader: (5)

[/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.

dpf22

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

marcus219

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

NZConvertible

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.

Raymr

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.