Stevan

iTrader: (17)

Where is the the 2.6L?, Where does the 180hp come from on a sp 13b? 1.3L?
It does have 6 chambers all working at the same time, I think its like a 6 cylinder.
Revolultions should have nothing to do with it, if you turn a v8 enough times to get the volume of all the chambers, the same should be done on the rotary.

rdharper

You be brighter than the average guys on this stuff. I've owned my 85 GSLE for a lot of years now, yet it was only last year that I worked this question of power stroke vs crank rotation. Tried to explain it to my brother (audi-lover). Took about a week... lol. But he got it.

Kind of got lost on the comparison when I realized it predicts more power than is actually present. Probably due to adiabatic differences... but don't know.

Other comment, I love the color combination in Rx7_AU (first post). Why do you say "My 85 S3 Rx7
*R.I.P*" ?

Richard Harper
Morgan Hill, Ca

gsl-se addict

iTrader: (3)

I loved it too. His car was recently stolen. They got it back but the thieves pretty much destroyed it. I guess the insurance company is going to total it. Too bad, it was a nice 7. Atleast he had full coverage on it.

mckinneyml

All I would say is imagine a buyer who is not knowledgeable on rotaries. The minute he gets the car home and sees the 1.3L label under the hood what's he going to think?

credible_hulk

Engine displacement has NOTHING to do with how many revolutions a crankshaft makes to produce one power stroke in an engine. Engine displacement is simply calculated by looking at the change in volume produced by piston, or rotor, movement.

Let's look at a reciprocating piston engine first. The change in volume is simply a cylinder, and as I'm sure we all remember, the formula for calculating the volume of a cylinder is V= pi X radius (squared) X height. Translating this to engine speak, we have: V= pi X bore (squared) X height. Now, let's see this in real world terms. The new Chevy LS2 engine has a bore of 4 inches, and a stroke of 3.62 inches. This gives a single cylinder displacement of 45.47 cubic inches. Multiply this by the number of cylinders, and we get roughly 364 cubic inches, or 6 liters. Notice that nowhere in this calculation did we bring up the fact that the crankshaft must rotate two times between power pulses. It is a minimum and maximum volume deal here.

Now, since I am a little rusty on my calculus, we will take Mazda's word that the difference in the volume produced by rotor movement is 654cc (for a 13B). Multiplying this by the number of rotors we get 1308cc or 1.3L.

2-Stroke engines use the same formula as a 4-stroke, since the difference in volume produced by motion of the piston is the same.

credible_hulk

Said another way, the displacement of an engine (any engine) is the change in volume between TDC and BDC multiplied by the number of cylinders (or what have you).

Pele

iTrader: (28)

I think they only used one rotor face to calculate that volume since only one rotor face is in use at a time... Times two rotors.

Mr_Rx7_Au

Pele, I think you are right there.

Why do I have R.I.P? Well, as Kent said, my S3 got stolen, vandalised, and written off. You can read about it here by doing a search using my name as the author. I havnt put the pics up yet of what they did but I must find time to do it. Read about it here:

https://www.rx7club.com/showthread.p...ght=rx7+stolen

As for the somewhat heated argument on here, Guys, I'm not saying what he said isn't techincally conceivable or right, my whole argument is that the motor is a 1.3. Ebay puts that section for people to state the engine size, not for distorting the truth. It looks funny as hell because on the title its a 13b then he puts a 2.6litre engine as the size. It's not a piston 4/6cylinder 2.6litre!!! regardless of how much power it would produce, and how much that would rate, the fact remains it is a 1.3, and has been that way since 1983 when the 13B came out.

Anyway, some really good info about how engines are measured.

REVHED

The 13B was produced LONG before 1983. lol

Rogue_Wulff

The debate about the "real" displacement of a Rotary engine has gone on for many years, and will likely continue long after some of us are dead and gone.
All 3 sides have valid points, and I won't force my opinion on anyone.
Mazda rated the 13b as 1.3L, great for bragging rights after outrunning a much larger displacement engine.
Many santioning bodies use the 2.6L as a "Comparable" displacement, since that is the amount displaced in 2 revs of the engine, similar to a 4 stroke piston engine.
The total displacement is 3.9L for one rev of the 2 rotors, 3 revs of the shaft.
I prefer to just call it a "13b", like many other engines that have a model designation.

REVHED

Best post in the entire thread.

DS2000

Just to add my 2 cents, in the UK the FD is registered as a 2.6l engine, cars with a 1.3 get a taxt break for good emissions.

I'm in the process of getting my FD dropped to a 1.3

13B4port

You beat me to this post, but that's not where the arguement comes in. The measurement only measures 1 surface on both rotors instead of all 3. so it realy all depends on how you inturpret the rotory engine. The equation for engine displacment is simple, volume of one combustion chamber mutiplied by the number of combustion chambers gives you engine displacment. Do you class each face on the rotor as a new combustion chamber or do you class only the compresion side of the housing as the combustion chamber. We are talking _CHAMBER_ here not combustion surfaces. The piston on a v8 isn't considered the chamber but the definition of the combustion chamber in the mechanics blue book is simply the location to which the compressor (ussually a piston) travels in the block and head where combustion takes place(i gave the jist of the deffinition because it was realy long). So you apply that to the rotory and you cannot consider each of the surfaces of the rotor to be by _definition_ a new combustion chamber. So considreing the rotor is your compressor it cannot have combustion _chambers_ but it can have combustion surfaces. So if the rotor can't have combustion chambers then that means the housing during the compression cycle is the combustion chamber because that is the common place where combustion happens.

That's why i consider the 13b a 1.3 but then again i could be way off base.

credible_hulk

I think I may have confused some people with my long winded post. The 13B is 1.3 L. Displacement is measured during only one part of the combustion cycle. Therefore, displacement is measured only on one rotor face, just as it is measured by the distance a piston travels in one stroke.

hammmy

This entire discussion is rapidly becoming useless. Mazda rated the motor at 1.3L, the guy should have said as much on the auction, and HP and torque are the only good comparative quantifications for engines.

saltyslug

You should call it what it is 13b 1.3 liters, after all ford calls the 4.9 a 5.0 and what do we call all the mustangs we see??? 5.0's, cause thats what they called it. I cant wait to tell people they just got thier *** handed to them by a 1200cc engine.

Mr_Rx7_Au

I meant when it came out on the Rx7, since this started on the guy who was selling his 13b rx7.


You said it.

Sterling

Au, the Ebayer really isn't that much of a moron, and it really wasn't that funny.
I've certainly seen a lot more misinformation right here on this forum, and it's often easily corrected with a bit of friendly educational guidance, which of course, usually does not include calling the misinformed a "moron".

This whole rotary vs piston displacement thing is of particular interest to me because I see it in terms of cfm for my carb work. Nothing more.
But here we have arguments that amount to about this:
"My ORANGE is really like it's twice as big as your APPLE because it's three times as juicy!"

The rotary engine is a whole different animal, magnificent for its simplicity. To compare it to the piston engine strictly for performance measurement is to relinquish that magnificence to a dinosaur of design with a 160 year evolutionary magnificance of it's own.
The only validation in my mind for such a comparison is due to the fact that performance automotive parts are manufactured with the piston engine in mind, and must be adapted to our fine rotaries. Therefore, for me, it is only the volume of air that enters the engine during one rotation of the crank that matters.
Since the rotors spin at 1/3rd the shaft speed, in a 12a engine, only 70 cubic inches ever enters with each shaft revolution (at a theoretical 100% VE). -Same as a Pinto 140 cid.
So just recall this thread when you're determining the needs of your 12a, and remember that its needs are the same as a 2.3 liter Ford 4 banger that can rev to 9K, and think about how utterly scientifically stupid it is to put a Holley 600 cfm carburetor on such an engine.

(Credible can do all that "calculus" for ya.)

rotarypowerrx7

lol

rotarydude

iTrader: (2)

Die zombie thread Die.... return to the grave

WingleBeast

iTrader: (1)

1.3 rotary are rated at 2.6 in racing classes, so if it was a race ready car, this makes sense

Sgt.Stinkfist

iTrader: (6)

lolz. sometimes i wonder how certain threads, esp. odd ball ones like this, get brought back from the dead

elwood

iTrader: (1)

A lot of interesting viewpoints here, however I see most of this stuff as academic.

Displacement is only important in some countries for tax purposes (as was mentioned by one post already). Since I live in the USA, and I think it's the center of the universe, displacement doesn't matter much to me -- only how fast the car is.*

I put horsepower in the same bin (almost). It's nice for bragging rights and talk around the water cooler, but in reality, it's only useful when teamed with a bunch of other elements that make a car fast -- and that's what really matters to me.

*The displacement thing is interesting to me because there's a bit of snobbery attached to high specific output / low displacement engines. Many auto enthusiasts look at US OEM engines and say they're low tech and less desirable because they are larger engines that offer similar levels of performance. What they're missing is that it's a performance vs. $ equation for the US OEMs, and they simply don't care about displacement. It's a simple fact that it's cheaper to put in a bigger engine than add double overhead cams or forced induction, or whatever . . . and the car doesn't care what displacement the engine has.

Bryan Jacobs

iTrader: (66)

wow, resurrecting a 7 year old thread

Kentetsu

Dusty in here.


(SCCA classes it as 2.6)





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