Now you got that exactly right... makes me wonder how you can miss the rotary part.. you have a great grasp of the basics

 

your going to make 620+whp NA!
props to you.

seems you were only thinking 2 rotors. 4 rotors can make alot of power NA.

 

thank you! glad to see someone that appericates it.

are you being serious or just kidding around?
i am about 3k deep into the 496 and will have to spend another 3-4k to finish it up... gas mileage??? i dont want to know, esp with 4000 stall....






besides... it is going into my chevelle
you cant possibly think a little 13b would do any good in that... i will need 2 speed axles and 7 speed box to get it moving.

 

https://www.rx7club.com/showthread.p...ning+resonance

PHYSICS. APPLY DIRECTLY TO THE FOREHEAD!
PHYSICS. APPLY DIRECTLY TO THE FOREHEAD!
PHYSICS. APPLY DIRECTLY TO THE FOREHEAD!

Physics still applies to rotaries, even if you're a stubborn twit who doesnt comprehend accousting tuning theory and cant seperate the lack of restriction of a new exhaust vs the stock, from scavenging from a properly set up exhaust!

You're doing the same old "I said so" bullshit without isolating the variable or saying... squat to address the theoretical variable. Well, that and the two exhaust ports of a 13B have exhaust coming out very similar to the exhaust coming through the first step in a 4-2-1 header on a 4 cyl engine .

I simply dont know why you can reject fact and theory and replace it with bullshit and then say I have a 'lack of understanding the basics' when you spew "exhaust stacking" after your emotional OHV-hating nonsense.

You dont know what you're talking about and hiding behind an arguementative ploy and basically resting on the fact that "well someone sells a true dual so it works and I saw it make a dyno gain vs a stock exhaust." No ****.

Get a paired header with the right length and compare that to a 'true dual' and that to a stock manifold with every other variable (intake, porting, fuel metering, dyno, day, bla bal bla) the same and then say its better, or at least come up with a rational basis on which you're rejecting exhaust scavenging on a rotary... even though it has its exhaust in pulses just like basically any other engine just like you have to sit down when you **** just like everyone else, instead of an appeal to authority, ok?

I DO understand the basics and what I'm talking about and you have no rational or empirical basis on which a 'true dual' would do any better thair a paired header at all or be worth the weight and effort. Its style over substance, plain and simple.

 

Rotaries have exhaust come out in pulses too! It comes out 180* of E-shaft rotation apart alternating between the two exhaust ports of a 13B. That makes it VERY, VERY, VERY easy to make a paried header work for scavenging if you just plug in the EGT for the fuel you're using and the peak rpm you want to tune it for.

Its only two ports for christs sake! You could probably chop the top 4 pipes on a tri-y and bend it and use that. Rotaries just need one step to scavenge properly... rotaries are not that different, they just have higher EGTs so the exhaust pulses move faster, but all that changes is where you put the collection vs rpms, nothing more.

 

Okay. Again, you just don't get it... I am not comparing a stock exhaust to an aftermarket exhaust at all... but you don't get that. I am comparing a aftermarket system with another aftermarket system. The thread you linked too has some great examples of tuning lengths based on RPM and port size, but what you seem to be missing is where do you want the whole band of power to be... Sure you can tune for one peak RPM (and be crap on everything below that), but whats the point??? You want consistent power for the whole band width. Something that the true dual provides without worrying about the cancelling effects of a collected system at lower than tuned lengths.

But you seem hung up on the collected header design... (which is proven only marginal gains with standard stock porting) over countless other designs. So back up what youa re saying with real world examples on ROTARY engine applications. Prove it in the real world as I, RB, Mazdatrix and countless others with decades of real world rotary experience have. Instead of hiding behind your conventional engine physics.

Perhaps you should have read this in that thread that you are holding up:
So much like rotarygod said:
So, I am done with this.

Much like the sway/stabilizer bar and E-shaft- Crankshaft arguments, I can only lead you to the light. Only you can change the god you believe in. I neither want too or can make you accept it.

 

CONVENTIONAL ENGINE PHYSICS? What kind of pseudoscientific bullshit is that? WTF is your major, political science?

It was already explained in great detail in a thread I linked to with all of the science and theory behind it, you just either cant understand it or refuse to look, and Im NOT repeating it again.

The reason that Rotarygod said that hes sick of the debate is stubborn tools like yourself who cant look at a fact and recognize something, and instead just stick to your stubborn misconceptions and block everyone out like a creationist in a debate or the typical ricer in most internet forums, such as what you're doing now.

Rotary engines are not very different from any other internal combustion engine, its just that the differences are enough to make fanboys of rotaries think they're special. The laws of physics apply just the same, pulse-tuned scavenging works exactly the same on a 13B as it does on any other piston enigne, and you are so lacking in comprehension of the theory you paste something that SUPPORTS THE POINT I WAS MAKING THE ENTIRE ******* TIME.

Two LONG *** pipes only have a resonant advantage at VERY LOW RPMS. Its a ******* rotary engine, not a semi truck, you dont want the runner lengths of two 'true dual' exhausts that would only work around idle. the BEST solution would be proper pairing, and then dumping the exhaust the proper length from the collector, but you dont understand that, and youre apparently too stupid to look at the provided solutions for different runner lengths relative to what RPM you're trying to tune them for.

Sure, duals can work with a resonant rpm useful for a rotary engine if they dump out of the fender well, but not as good as if you paired them for scavenging AND had the right lengths past the coupling but as long as they would have to be to go the length of the car you're basically preventing yourself from having any scavenging advantage at high rpms and instead giving an insubstantial advantage in an rpm range the rotary sucks a big fat one at... idle!

What really kills me is thats been very clearly explained, and he gave examples of what lengths for what rpm range, and you jsut block it out. Im not going to accept something thats completely wrong to "Respect your opinion" becuase its completely nonsensical.

 

This is for the people who are new to the thread to see what I mean: https://www.rx7club.com/showpost.php...42&postcount=7 <- look there. Oh, but Ill do one more and post what he posted!

To tune at 6500 rpm (stock intake tuning frequency)
This is the best number to tune for based on stock gearing.
short primary: 23.1"
long primary: 95.4"

@7000 rpm
short primary: 21.37
long primary: 88.5"

@7500 rpm
short primary: 19.89"
long primary: 82.54"

If you used the streetport template on the exhaust
@6500 rpm
short primary: 21.8"
long primary: 90.2"

@7000 rpm
short primary: 20.17"
long primary: 83.69"

@7500 rpm
short primary: 19.89"
long primary: 82.55"

I really dont understand what the problem is, TBH. Tuning for a resonant RPM range based on length to the collector from the exhaust ports works the same on ANY engine, rotary, piston, 4 stroke or 2 stroke, its no different. Rotaries are different, but not so different that the laws of physics dont apply - but there is so much misinformation and bullshit you run into nonsense like this, and this is probably to blame for a lot of the drama between rotards and non rotards.

 

You even hit/repeat my points and you don't see.
Yep, he did... what happens under that RPM??? What happens at 4000 RPM when a collector is tuned for 7500??? Man- what don't you get about that???

Maybe you like pissing away all your power at 4000 rpm so you can have it at 7500... I don't. Most people don't drive at even 5000 RPM. You don't get the cancelling effect at 3000 RPM because the {edited} header is tuned for peak power at 7000 or higher.

again, since you are unwilling or unable to see any answer (even when it was clearly posted in the quote I posted), and you continue to badger and attack calling things you don't have even a grasp of as ..lets see "pseudoscientific bullshit " and other comments (did your eyes just glass over when a post says something that you don't agree with, so it must be BS??) it again is clear you just don't want to get it. Its not that you don't get it... you don't want to get it.

So again I am done... you can attack and insult just like some newbie all you want... doesn't make you right.

Maybe try and get out and actually design and build a couple headers and free flow true dual system yourself and compare them. Maybe then you would {edited for content and flaming}.

Have you even ever built a header for a Rotary engine?? Built an exhaust for a rotary engine??? You can come by my house and find different ones hanging from the ceiling of my garage and stuffed in the storage house on the side of my house.

Otherwise just shut up. As I am done, and will not further reply to you here.

 

do these also apply to Turbo Rotaries as well? I see N/A stuff, but is turbo somehow different, or does the turbo exhuast side mask the pulses or some ****?

 

All that I have posted in this thread and my exhaust experience is with non-turbo rotaries.

I cannot say how much carries over, but unless you are running two turbos it would impossible to do a true dual exhaust system on a Turbo

 

Um exactly what youd assume would happen, it doesnt get the benefit of the exhaust tuning. Plus stock its tuned for 6500 rpms anyway... so I dont know why you're bringing up a hyperbole about tuning for an rpm its not unless you made one that way.

But thats exactly my point! Those "true duals" get ZERO scavenging, and are so long their heimholtz resonance is at such a low rpm its completely useless. I dont have to design a bad header to know it wont work, and you shouldnt either.

Thats called a TRADE OFF! But the thing is, an exhaust set up for high rpms doesnt really HURT low rpms, it just doesnt give an advantage like it would at those high rpms. But when you tune NA you cant have it work over the whole rev range unless its a low revving motor... but you hate OHV motors, and like rotaries... wtf? You cant make a NA rotary fast unless you're willing to rev it the hell up. How could someone with an IQ over 80 whine about the power of a NA rotary at 4K rpms??

The reason Im getting fed up with you is becuase its explained very simply, and then you say you get it, I dont, and say something as stupid as what I just quoted. If you want power at 4000 rpms then get over your OHV hatred and get a damn small block! "True duals" arent going to give any signifigant power at 4K rpms and its gonna kill your high end compared to a properly set up runner. Plus any porting pushes the powerband up as well - I REALLY dont get what it is you're trying to make here.

Its a ROTARY ENGINE, if you want to make power you have to pick a high (but not too high) rpm to build it to be efficient for, but more around 6500 or 7000 rpms, not some stupidly high figure at redline. You want to put the peak power rpm to be before the redline (we call this a "power band") and build it accordingly because you are going to get nowhere fast to build a 13B for low end in any car on the heavy side of a Caterham or a Lotus 7.

And no, you cant build an exhaust to be good at all rpms, but while 'true duals' can remove restrictions, they give no accoustic effect except at VERY low rpms. If you want a 13B to be fast, get a turbo, or rev it the hell up. If you want to have your cake and eat it to, get an actuated 6 port setup working, because different ports are efficient at different rpm ranges, and Im sure you know that, and let a well designed intake help give it efficiency at low rpms by closing the 5&6th ports.

A well designed header to give an advantage at high rpms wont HURT low end, but it wont give an advantage to low end. It sounds like you think 'true duals' are somehow better, but Ive seen no evidence that they are, and everything you have to say is emotional and devoid of any comprehension of what I'm talking about.

You still dont get it and whining doesnt make you right. This has been beat into the ground, you just dont understand, thats all there is to say. All of your arguement is an appeal to aruthority or experience, and say "well if they sell it, it must work". Doesn't work, sorry.

 

Can I get this in non-engineer / retarded form?

 

The speed of sound in the exhaust of a car is a constant - and temp determines the speed of sound, not pressure, but anyway...

For the best performance you want the pulses coming out of the engine to line up exactly 180* apart - that is, the peak power from one pulse coming in right behind one, because behind that pulse there is a lower pressure area. This effectively uses the inertia of the gas to help suck the gas out of the engine and reduce backpressure, and this "scavenging" effect can even help suck air into the engine (overlap).

There is also another way to tune for an rpm, heimholtz resonance - the length of a tube will have a resonant frequency relative to the length of it - longer tube = lower tone, or lower rpm. Its just like with a recorder or a flute or an organ pipe!

Paired scavenging exhaust (headers) primarily rely on the first effect, but heimholtz resonance can play a role in full custom race exhaust as well. When you dont pair off your exhaust pipes like what he supports, you have a heimholtz frequency for a very low rpm and no scavenging, and Im arguing that youd want to pair them off for scavenging, and if you desire change the length from the whole exhaust to the tip to get a secondary effect from that as well.

Intakes work through pulse tuning and heimholtz resonance all the time - the variable intake in a FC works with pulse tuning by having a longer path for lower rpms, and then opening a valve to give it a 'short cut' so it works at higher rpms, and the 787B's motor used heimholtz resonance by changing the length of the throttle bodies based on rpm.

It works in a rotary just like in a piston engine or any other internal combustion engine that works on a cycle instead of constant burning like a turbine. The issue is the lack of comprehension about rotaries that MOST people have (rotarygod DOES understand them, however) and adjusted the formulation to work properly. Another funny thing is most intakes assume static timing on the intake for changing runner lengths - but actuated ports on a rotary are an ANALOGUE to having different sets of valves with their own 'cams' on a piston engine so a really good custom intake would be relatively complicated for a 6 port, for example - but a 4port wouldnt be that hard.

At any rate, I've tried to explain this over and over, the laws of physics dont change or care that its a rotary and not a piston motor - its just that most people dont know how to apply them.

 

gases are fluids. a fluid is something that can't sustain a shear stress without deforming.

 

Gas expands...

 

well, what are you asking??? What is the best set up for exhaust???is that what you are asking???

For a stock system:

If you follow Nihilanthic's internet based thoughts and book study, a tuned length header will give you the best power particulaly at higher RPMs. Based on this if you went back the the originators question, it might be possible to tune a crossover pipe for this. The drawback is that a higher peak somewhere in the RPM range, would probably mean a drop somewhere else. A classic example of this would be a car that is a dog from the stop light (even more so than rotaries typically are) but have a great 0-100 time.

However if you follow my real world experience, true duals are the the best for low end and midrange power (where again you need it most in real world applications). This keeps a consistent raised power band through the entire usable RPM range.

And I am sure based on Nihilanthic posts and my opinions, that a manifold back single has few advantages on a non turbo, other than weight and cost savings.

For modified intake (such as a carb, or custom tuned intake runners), or more than minor street porting changes:

Then you would want to tune according to the intake. This (IMO) is the best and only time to use a tuned collected header, as then the low RPM drivability is probably shot anyway, and you are going for peak power rather than everyday drivability with flat linear power/torque.

 

on a side note didn't JIMLAB make something around that with his NA LT1

 

Yeah, that was what I was wanting.

 

Ice, thats BS, a collected header wont hurt the low end over stock, and neither would a properly set up intake. If the porting is stock or 'street' ported it wont change the character of the car that much.

Speaking of LT1s, did you know that they have a tuned length in thier manifold best for about 8000 rpms! You seen the dyno of one?

Flat as nebraska until drop-off because the cam is about 180* in duration @.05" lift or so and its got shitty manifolds and soft valve springs, but thats beside the point. A lack of advantage doesnt mean a subtraction of performance - a well set up paried header with the proper length main pipe and a no restriction muffler would not hurt anything on a street ported motor, but a stock exhaust would choke up a ported motor, just like a stock intake can choke up a ported motor.

Yes, I know its NOT A ROTARY, but the accoustic effects change the shape of the curve - the displacement (and lack of restriction to make it nose over after a given airflow demand limit [power] has been exceeded...) determines how much torque and power it has, but the SHAPE of the curve over rpms is determined by the resonant tuning of the intake and exhaust.

Unparied duals as long as the length of the car are going to be for such a low rpm it would be effecitvely useless unless you're going by the 8th reflection or so. But at any rate, if you want a header set up for low rpms, you can do what they do for headers for low rpms on ANY OTHER CAR - MAKE THE PAIRING FARTHER AWAY FROM THE EXHAUST PORTS. Losing the scavenging effect is a real detriment and you cant make mega low end without filling the ports with JB weld or moving them back somewhat anyway.

At any rate, its a 13B. If you want it to be 'torquey' use smaller tires, or a numerically higher rear end, or drop weight. It will never make a lot of torque without a turbo and wont make it at low rpms without making it into a 20b or a 26b. If you want low end, get a Diesel or a piston motor. sheesh.

 

As warning if this thread gets into V8 engines much further it wil be shut down. V8 threads belong in the Other Engines section of this board and do not apply to any RX-7 technical section.

 

Neither a single nor a dual pipe cools the exhaust much. Twice almost-nothing is still almost-nothing.

Bigger pipe => slower flow => less resistance. We studied both liquids and gases in fluid dynamics class. And I deal with them at work as well. A huge exhaust is the 'sledgehammer' approach: maybe there are lighter or slightly more effective ways, but it'll do the job. In fact, going too big is just a waste of $, especially on a dinky N/A.

Losses from a large Y pipe is negligible, and turbulance is nigh non-existant. I deal with air pipes thousands of feet long at work, and the losses are still small (even with bends and Y's and so forth). ~10' really isn't that long (even w/ the Y). In a ~10' pipe you lose far more from exit velocity (powering your leaf-blowers/tail pipes) than you do from wall friction. And even that is small. Losses are far greater in the cat and mufflers. The sharp bends in the header come next. Deal with those and then you can shave off a fraction of a horsepower worrying about the pipes.

Below ~200mph exhaust gas is treated as an incompressible fluid flow (just like a liquid). Assuming constant temperature and pressure, it does not expand nor contract. Fluid dynamics applies to both liquids and gases.

 

The problem with that; is on a non turbo is that the mixture is still burning and expanding halfway down (even with cats). This is what the classic rotary lift throttle "back fire" comes from when the ACV is not functioning.

The exhaust doesn't have the benefit of cooling from being forced past a valve and head (as on a piston motor) or a Turbo which further mixes up the waves and cools from the impeller; both of which stabilize the exhaust mixture to a more consistent temp and pressure.

But yes, if the exhaust mixture was static (Constant temp and pressure or as far as reaction while inside the pipe), then yes every thing else you say is correct.

 

A lot of that is the state of tune and lack of decel fuel cut. Put a real standalone on a RX7 vs a carb or the mazda ECM and you could tune that out, ESPECIALLY on a NA car.

Also, the "cooling" that exhasut gas gets on piston engines tends to be more adiabatic - they use more heat from the charge to make power than a rotary engine does! This is OLD news.

But, if you have a piston engine that isnt running efficiently, with retarded spark or too lean of an A/F R, you'll get glowing exhaust, even if you're blowing through an exhaust valve.

 

The problem with tuning out the after burn, is that Mazda typically richens the mixture up, as the mixture becomes part of the lubricant.

So while you can tune for better lift throttle burn, but at the cost of engine longevity. I call that a tuning choice or inherit design problem of the rotary. Reduced gas mileage of course is the other nasty side effect.

So, unlike a piston engine (again), the richer mixture adds longevity with only minor power losses, as opposed to a poorly tuned conventional 4-stroke engine (not including Miller cycles- which are closer to the rotary design as far as induction, but much leaner than a rotary- seal Lubrication is not part of the mixture.) Richer mixture in piston motor has no effect on longevity.

So, again, (and now this parallel does fit to a poorly tuned piston engine) the exhaust tune becomes difference, as the last thing you want is the expanding combustion process to be happening close enough to the engine to force the exhaust mixture back into the other rotor's (or cyl) exhaust (and again more of an issue, as the rotary doesn't have the 2ndary purge of the combustion chamber like a 4 stroke piston motor does- but rather a single vent cycle like a 2 stoke).

In a perfect world, you would have your completly burned mixture stacking up like this:
1.2.1.2.1.2.1
Regardless of RPM, or load; all the same size and timing.

In which case the tuned collected headers work great. All the outputs of the 1 stack up just behind the 2 at the collector.

What throws the wrench in, is the on-going combustion.

So could end up with this:
1.2.1.2.1.2.1.2.1. etc

Because of the shockwave from the on-going combustion.

Now on a 4 stroke piston motor, the exhaust valve tends to deflect that shock wave slightly (in therory you really don't need too though because the piston is forcing the exhaust out the direction of the open valve and it's closed all other times), but with a 2 stroke or direct port (like most rotaries except reni's) there is little to deflect unless the port is closed- and lets face it... it's never really closed on a peripheral exhaust rotary.


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