GtoRx7

iTrader: (5)

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-***. 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.

dpf22

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

Zach McAfee

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.

Orange!FD

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?

Swift_7

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.

MikeC

Well this will really **** 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.

604Ryder

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

Drifter101

agreed about that 2.6 L consumption

Dltreezan

iTrader: (3)

this should be in the lounge

snub disphenoid

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.

$150FC

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.

Speedworks

And guess what my Belgian car owner paper says?

2600cc.

go figger

MikeC

Do you have a paper number?

MikeC

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

NZConvertible

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".

fcfdfan

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.

MikeC

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

fcfdfan

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?

MikeC

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

MikeC

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.

AcidSlasher

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

KevinK2

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?

MikeC

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.