Originally posted by Icemark
#1 too bad you didn't put in the majority of the sources to confirm it... otherwise it is no different than any other person spouting off on the internet about he or she believes. However as noted in #3 there are a few of the views that are applicable.

#2
The majority of your arguments are using piston and carbed 4 stroke engine analogies which don't hold up in a fuel injected rotary because of very basic design concepts.

#3 your post of this:
is much more appropriate in the case of a rotary, since its inherent design is basicly a two stroke.

Perhaps you should read the texts youself, unless again you were wanting to prove my point on the operation of a rotary motor (not a piston engine running in a 4 stroke design).

Originally posted by Icemark
I am glad you posted pauls listing as it 100% agrees with what I am saying:



This is the whole concept of what I am refering too

Too big pipe= not enough back pressure to gain sufficent velocity

Too small pipe= too much back pressure and loss of HP and compression

Just right tuned for the engine pipe= best power gains.

Originally posted by Digi7ech
Well I understand on piston engines you need some backpressure. Don't exactly know for rotary but guess you need little to none.

I heard that backpressure on a piston adds a bit of torque. Don't know how though(scavenging or something).

Also if you run open headers I heard you can sometimes suck in cold air and **** up the hot valves by distorting them.

The intake portion of our combustion can kind of be considered pull but it is still pushing.

Originally posted by rxspeed87
ok most of that article was written by me using iether my text or quoting from other people

if you wish you can find the article over at thirdgen.org

but a rotary is not a 2 stroke
it has 4 VERY seperate intake/exhuast/combustion/compression strokes

will covor more later cause I'm running out of time

but should be able to explain it a little better

Originally posted by Icemark
On a N/A some back pressure is required, as part of the way a rotary works is that the some of the unburned gas (and some of the burned) gets pulled back into the next combustion cycle in that rotor face.

If there is insufficent back pressure, emissions go way up, and HP goes down as all that unburned mixture is forced out, instead of helping the next combustion cycle (the unburned mixture obvously helping richen the next burn, and the burned mixture, helping lower the combustion temp in the next burn so that it burns longer- a sort of built in first stage EGR). The new Reni motor uses this same principle to a much further extent, where the exhaust is actually routed through the side to feedback into the intake stream.

So the big key is to get a system that is not too big and has a little back pressure, but not as much as stock.

For example if you were to use the HKS 60MM system for a turbo on a N/A you would have less HP and a lower torque curve than if you used the 50MM system.

Why??? because the bigger 60mm system flows better and has reduced back pressure.

So biggest fastest and no back pressure only applies to Turbo cars... on N/A cars it is manditory to have some back pressure for increased torque and HP. Anybody that says that zero back pressure is a good thing doesn't understand even the basics on Internal Combustion motors.

Originally posted by Icemark
Hmm, seems like a lot of it was written by someone working on old piston engines and not applicable to a two stroke engine.

But, please do explain why you think that a Mazda rotary is not a two stroke.

Two stroke engines use a constant operation, while 4 stroke engines use a dead cycle. The Mazda rotary does not have a dead (non power generating) cycle in its operation.

Now if you didn't have a power cycle in each rotor face in a single revolution, then it could be considered a 4 stroke engine.

Originally posted by Icemark
#1 too bad you didn't put in the majority of the sources to confirm it... otherwise it is no different than any other person spouting off on the internet about he or she believes. However as noted in #3 there are a few of the views that are applicable.

Originally posted by Icemark
again, your post is more applicable to a turbo rotory or a 4 stroke piston engine.

If indeed the most Hp was generated by the least amount of restriction then running with no exhaust would provide the most HP.

But it doesn't

Originally posted by Icemark
I am glad you posted pauls listing as it 100% agrees with what I am saying:

paul yaw
This is called exhaust gas reversion. If the exhaust gas velocity is low, (Such as at low rpm) the vacuum created by the increasing chamber volume can easily reverse the flow and pull the gasses back into the chamber. If, on the other hand, the exhaust gas velocity is high, it will take a great deal more energy to reverse their flow, and the result will be less exhaust gas dilution. This is why large exhaust ports, and large diameter exhaust tubing reduce low speed power.

This is the whole concept of what I am refering too

Too big pipe= not enough back pressure to gain sufficent velocity

Too small pipe= too much back pressure and loss of HP and compression

Just right tuned for the engine pipe= best power gains.

Originally posted by gotdatfiyah
is the 2" i have fine on my gxl then?...would i benefit from getting 3"?

Two-stroke engines do not have valves, which simplifies their construction and lowers their weight.
Two-stroke engines fire once every revolution, while four-stroke engines fire once every other revolution. This gives two-stroke engines a significant power boost.

On one side of the piston is the combustion chamber, where the piston is compressing the air/fuel mixture and capturing the energy released by the ignition of the fuel.
On the other side of the piston is the crankcase, where the piston is creating a vacuum to suck in air/fuel from the carburetor through the reed valve and then pressurizing the crankcase so that air/fuel is forced into the combustion chamber.
Meanwhile, the sides of the piston are acting like valves, covering and uncovering the intake and exhaust ports drilled into the side of the cylinder wall.

The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work.
Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful.
When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down.
Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tail pipe.

Originally posted by rxspeed87
icemark get on AIM

my user name is rxspeed87

same as what you see here

After a great deal of thought, I decided that this first article should cover the basic workings of the rotary engine. In my experience, most people have the hardest time understanding port timing, and how it relates to engine operation. The accompanying illustration from "The Rotary Engine" by Kenichi Yamamoto will make this much easier to understand. At first, it may seem a bit confusing, but if you simply follow the numbers in order it is actually quite simple. Rotary Engine Picture

Before going into detail, it is critical that the reader understand some basic terminology. The various timing events of an internal combustion engine are typically stated in degrees of crankshaft rotation. In our case, output shaft, or eccentric shaft rotation. This terminology comes from the piston engine. Top dead center, or TDC refers to the working chamber being at its smallest possible volume. In a reciprocating piston engine, this occurs when the piston is at the very top of its stroke, hence the term top dead center. Bottom dead center, or BDC refers to the chamber being at its largest possible volume. In a reciprocating piston engine this occurs when the piston is at the very bottom of its stroke. All chamber volumes between TDC, and BDC, are referred to as Before TDC (BTDC), after TDC (ATDC), before BDC (BBDC), and after BDC (ABDC). For instance, 45° ATDC refers to the point at which the eccentric shaft has rotated 45° beyond top dead center. This is the situation in the first picture, looking at the chamber numbered 1. The line in the center of the picture extending from the crosshairs illustrates the angle of the eccentric shaft. This line coresponds with the keyway in the front of the shaft.

Below is a description of the complete process. Each description corresponds to the number in the illustration.

1. 45° ATDC The intake stroke is just beginning. The exhaust port has just closed, and on a stock or street ported engine, the intake port has been open for approximately 15°.

2. 90° ATDC The intake port is almost completely open, and the chamber is starting to expand at a fairly rapid rate.

3. 180° ATDC The intake port is all the way open, and has just passed the point of maximum flow. Maximum flow occcurs at approximately 135° ATDC, which corresponds with the maximum rate of chamber volume increase.

4. BDC of the intake stroke. The intake chamber is now at its largest possible volume. The intake port is partially open, and the port is still flowing in the forward direction, even though the chamber is no longer increasing in volume. This is due to the inertia of the column of air flowing in the induction system. This effect is referred to as inertial supercharging, and is described in further detail in the airflow section of my webpage. This will also be addressed in a later article.

5. 45° ABDC The chamber has started to decrease in volume, and with the exception of a stock US model 12A, which has an intake port closing of 40° ATDC, the intake port is still partially open. At high rpm, the intake port is still flowing in the forward direction due to inertial supercharging. At low rpm, airflow in the port has reversed, and some of the intake charge is being squeezed back into the induction system by the pressure of the intake chamber which is decreasing in volume. This is the result of the low velocity in the induction system. This is a very important point to consider, as this alone affects the operating range of the engine more than than any other factor.

6. 90° ABDC The intake port is completely closed, and air fuel mixture is being compressed.

7. 135° ABDC Same as #6.

8. 180° ABDC More of the same.

9. TDC of the compression stroke. The mixture is fully compressed, and ignition has started.

10. 90° ATDC The expansion cycle has started, and is already 45° past the point of maximum torque transfer to the eccentric shaft, which occured at 45° ATDC.

11. 135° ATDC The expansion stroke continues, but the torque transferred to the output shaft is now down to about 35% of its peak.

12. 180° ATDC The exhaust port is still closed, and the torque transfer to the eccentric shaft is approximately 15% of its peak.

13. 225° ATDC At this point, the exhaust port has been open for approximately 30°, and exhaust flow is quite high.

14. BDC of the exhaust stroke. This is typically the point of maximum flow through the exhaust port. Even though the chamber volume is not decreasing at an appreciable rate, the chamber pressure is very high, and this is responsible for a large percentage of the total exhaust flow.

15. 90° ABDC The chamber volume is decreasing, and is 45° away from the point of maximum rate of decrease of the chamber volume.

16. 180° ABDC The exhaust chamber volume continues to decrease, and at approximately this point, a bridge ported, or peripheral ported engine will have started to open the intake port.

17. 225° ABDC The exhaust port is still open, and the chamber volume is decreasing at a relatively slow rate. At this point, a mildly bridge ported engine will have just opened the intake port.

18. TDC of the intake stroke. Here we are at the beginning, ready to start all over again. Note that the exhaust port is still open, but the intake port, for a non bridge ported engine has not opened yet.

I have included the port timing for all RX-7 engines, and some alternative ports, so that you can make comparisons, and gain a greater understanding of how the rotary engine operates.

This information may seem very basic to some readers, but it is critical to the understanding of performance tuning. As most of you know, changing the port timing of the rotary engine can result in large horsepower gains. Further articles will discuss this in detail, and without this knowledge base, the upcoming articles will make very little sense.


Paul Yaw.

Originally posted by rxspeed87
ok the rotor dish does move away from TDC twice

TDC is defined as the spot in a motors movement that has the least amount of displacement

while BDC is the spot that has the most displacement


each of these events happens twice per combustion procces on a rotary motor

but notice how he said TDC twice

Originally posted by Icemark
based on what you have posted, TDC is only reached once. At the begining and end of a single combustion event (as demonstrated by #9 and #18)

Again, just follow his diagram on the numbers and you will see that the rotor face/combustion chamber only is exposed to the intake and exhaust a single time.

he only said TDC once in the beguinning of the cycle and to reference the begining of a 2nd cycle. At no point did he say the combustion chamber reaches TDC twice in a single cycle.

This is identical to the process in a two stroke, where TDC is only reached once per-cycle. The second TDC that he references to (identical to a two stroke) is the beginning of the next combustion cycle.

Originally posted by rxspeed87
TDC is reach TWICE though for a rotary motor

once at the begining of the intake
once again at the begining of cumbustion

same as a 4 stroke piston motor

a rotary at TDC is starting it's intake cyle. so thats one cycle

at BDC intake cycles is done with intake and now is working on compression... cycle 2

now we are back at TDC again with the intake charge compressed. and this is where cycle 3 starts. combustion

now combustion is done and the rotor is now at BDC... and starting the 4 cycle exhuast
this is where the rotor is moving back to TDC to push the exhuast out.


4 seperate strokes/cycles whatever you want to call them
strok cycle same thing
but do you see how you have 4 SEPERATE cycles

a two stroke motor only reaches TDC at begining of combustion and that is it