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-   -   (engine) 1.3 = 2.6 (https://www.rx7club.com/1st-gen-archive-71/engine-1-3-%3D-2-6-a-579965/)

RX(ZONE) 09-19-06 07:24 PM
(engine) 1.3 = 2.6
 
Alright i just need a quick explantion as to why the rotary engine is more equivilent to a 2.6 litre. I cant remember. lol

Theres a kid trying to say its more like a 4.1 one litre, and i need to tell him why its not. Thanks.

Blake 09-19-06 07:36 PM
Originally Posted by RX(ZONE)
Alright i just need a quick explantion as to why the rotary engine is more equivilent to a 2.6 litre. I cant remember. lol

Theres a kid trying to say its more like a 4.1 one litre, and i need to tell him why its not. Thanks.
He's probably making the (idiotic) argument that it's like a 3.9 liter. Anyway, the better way to look at it is that a 2.6 liter 4-stroke piston engine is like a 1.3L rotary engine, instead of the other way around. A piston engine total displacement is the sum of all the cylider displacments, but exactly HALF of those do any work on any given revolution. A rotary engine displacement is the individual "cylinder" displacment times 2 (two rotors). Each chamber has a 654cc displacment and there are three chambers per rotor, but it takes three rotations of the eccentric shaft for all three chambers to complete a full cycle...which means that there is one complete cycle per revolution for each rotor. In other words, all the displacement is used on every rotation, whereas a piston engine only works half as much for the rated displacment.

Instead of worrying about rated displacement, the correct means to compare them is "capacity". Capacity is the rating of the engines ability to pump air through them. For piston engines, Capacity = Total Displacment/2. For a rotary Capacity = Total Displacment.

RX(ZONE) 09-19-06 07:39 PM
Thanks man. :bigthumb:

PaulFitzwarryne 09-19-06 08:10 PM
Blake provided a good response. The only reason Mazda used the 1.3 figure was to reduce taxation which was based on 'capacity'.

The argument whether 1.3, 2.6, or 3.9 is the correct capacity has been around for the last thirty years without conclusion.

For most race regulations a figure of 2.6 is used in determining the division.

steve84GS TII 09-19-06 08:18 PM
For most race regulations a figure of 2.6 is used in determining the division.
Not that it ever helped the competition any,heh,heh!!

KeloidJonesJr. 09-19-06 08:24 PM
A 1.3 L can only turn into a 2.6 is if you add on another 13B!

Blake 09-19-06 08:24 PM
Originally Posted by PaulFitzwarryne
Blake provided a good response. The only reason Mazda used the 1.3 figure was to reduce taxation which was based on 'capacity'.

The argument whether 1.3, 2.6, or 3.9 is the correct capacity has been around for the last thirty years without conclusion.

For most race regulations a figure of 2.6 is used in determining the division.
I disagree that it has not been concluded definitively. 1.3L is the only logical rating whatsoever. Engines are nothing if not air pumps and air pumps are rated by capacity. Capacity best correlates to power output. The arbitrary rating of piston engines by multiplying cylinder displacment is flawed, but that system came first, so it is the "standard". So, by the standard, a 1.3L rotary is literally the equivalent to a 2.6L piston engine. The 3.9L thing is just stupid. The idea is that because piston engines are rated by a full cycle of all cylinders (2 revolutions) that if you used the same method on a rotary and considered each chamber as a cylinder, then the total displacment would be 3.9L over three revolutions. All that proves is how stupid the piston engine method is. The method employed by Mazda was to consider each rotor the equivalent to a cylinder and note that each rotor completes one cycle per revolution of the crank. It perfectly equates to Capacity, where piston engine are exactly double Capacity. It's so simple, I don't understand where the controversy lies!

Jozay721 09-19-06 08:28 PM
so if a 1.3 rotary is equivalent to a 2.6 is a 1.1 equivalent to a 2.2??

XLR8 09-19-06 08:39 PM
Do not try to compare rotary engines to pistons. Rotarys are not held back by a valvetrain. Why would a 1.3 liter engine be compared to a 2.6......or even a 4.1? I never did understand why someone would compensate displacement for a different design. Let me guess.....Someone doesn't understand rotaries and they want to make up excuses for their car getting smacked around my a 80 CI engine!

RX(ZONE) 09-19-06 08:53 PM
That exactly it! lol

Blake 09-19-06 08:58 PM
Originally Posted by XLR8
Do not try to compare rotary engines to pistons. Rotarys are not held back by a valvetrain. Why would a 1.3 liter engine be compared to a 2.6......or even a 4.1? I never did understand why someone would compensate displacement for a different design. Let me guess.....Someone doesn't understand rotaries and they want to make up excuses for their car getting smacked around my a 80 CI engine!
This is just about comparing Capacity, which is a mathematical excercise in equivalency of displacement. If you want to argue the thousand other dimentions of differentiation, be my guest. No one is saying that because a 1.3L (rated) rotary and a 2.6L (rated) piston engine are exactly the same capacity that it is the only means of comparrision. We could just as easily be discussing how a rotary engine is "equivalent" in weight to certain piston engine of the same weight. One kind of equivalency does not prove or even correlate to other kinds of equivalency.

jonjonwells 09-19-06 09:06 PM
So.... What your trying to say is.. Some of these cars are moving and we are not sure why.... I think I got it.

Hyper4mance2k 09-19-06 09:11 PM
A 13B IS A 1.3L!! I hate this shit. it only displaces 1.3L per revolution so it's a 1.3. If you have a 2L 2 stroke you don't call it a 4L just cause it displaces it's full displacement in one revolution. A 2L 4 stroke is a 2L engine a 2L 2 stroke is a 2L then a fucking rotary is a 1.3L cause that's all it fawking displaces...

REVHED 09-19-06 09:35 PM
I call the rotary a 4-cycle 2-stroke engine. It has the 4 distinct cycles of the Otto Cycle and it displaces it's full capacity in one revolution. It's a good way to confuse the piston guys. :D

clean85owner 09-19-06 09:42 PM
Mazda rated it at a 1.3; so, that's what I'm going to go with....

PaulFitzwarryne 09-19-06 10:33 PM
Blake; while I think you put forward a sound technical argument, I am happy to let the disagreement continue. When I use my car for Government trips, the rate of reimbursement is based on engine 'capacity'. My 12AT is officially rated as 2.2l so I receive the 2,000-4,000cc per km allowance. This is 44% higher than for a small Japanese sedan such as the Mazda 2, and what I would receive if the Government rated my engine as 1.1l.

I think you will find most European countries use 2.2 or 2.6 as the RX-7 capacity for road taxation purposes.

Rogue_Wulff 09-19-06 11:55 PM
My stand on the issue. Piston engines (4 stroke) displace the total volume every rotation, but only use 1/2 of it to produce power.
2 stroke engines use the full volume to produce power, but are not as volumetricly efficeint.
Rotaries have the volumetric efficeincy of a 4 stroke, and the power from every revolution like a 2 stroke.
Rotaries win.


BTW, a 12A would be rated as 2.3L, not 2.2L. 1146cc X 2 = 2292cc = 2.3L

KNONFS 09-20-06 08:06 AM
Originally Posted by RX(ZONE)
Alright i just need a quick explantion as to why the rotary engine is more equivilent to a 2.6 litre. I cant remember. lol

Theres a kid trying to say its more like a 4.1 one litre, and i need to tell him why its not. Thanks.
The most logical\simple explanation I've seen was by Evil Aviator:
Originally Posted by Evil Aviator
I think I can explain displacement in simple terms so that you guys can stop beating this dead horse. Do you understand the difference between a piston and a cylinder? Well, displacement is based on the cylinder, not on the piston.

For example, a 4-Stroke V8 may be rated at 5.0L based on the displacement of the swept volume of all its cylinders, no matter how many times the pistons produce a combustion cycle per crankshaft revolution. Now make that same engine into a 2-Stroke, and it is still rated at 5.0L, regardless of the fact that the pistons now have twice the combustion cycles as before.

OK, if you are with me so far, now look at the Wankel engine in the same manner. Its displacement is based on the swept volume of the rotor housing (cylinder), and it doesn't matter how many times the rotor (piston) produces a combustion cycle. The fact that the rotor has 3 faces has absolutely no bearing on the displacement of the rotor housing. In a similar manner, if there were such thing as a piston engine with one cylinder and three pistons that alternately traveled into the cylinder, its displacement would be based on the swept volume of that one cylinder, not on the 3 pistons.

Does this make sense now?
Full thread:
https://www.rx7club.com/showthread.p...t=displacement

vipernicus42 09-20-06 11:28 AM
Yes, Evil Aviator's post means that the DISPLACEMENT of the engine is 1.3L

But I like the explanation relating to CAPACITY as a way of explaining why a 1.3L rotary can perform in class with 2.6L vehicles.

So the question "What's the rotary's displacement in comparison to a piston engine" is answered with "1.3L"

but the question "Why is the rotary engine capable of producing the power of a piston engine of double it's displacement?" is answered with "Because it's capacity is equal (since in rotaries displacement=capacity but in pistons displacement * 0.5 = capacity), so output would be in the same ballpark"

Jon


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