rotarygod

iTrader: (1)

Damn link didn't work! Try this:

http://www.mae.wmich.edu/faculty/hat.../Lecture08.ppt

drago86

Thank you for the link, however, what reads .ppt files? I Absolutly understand what you were saying about total intake runner area now, I was once again wrong. I was unaware of the T2 manifolds equal runner lengths, a ive only ever had an NA and am only really familiar with the S4 manifold, though i have studied pictures of how the Vdi system works, its very interesting how the T2 manifold is true equal length, whereass the NA's wernt, sounds like they did a little more R&D on the T2's. Was this corrected on the Vdi equiped cars?

-*The S4 torque curve just happens to go down by 5000 because the horsepower curve is leveling off. Give me any horsepower curve and I can transpose the torque curve on it using only the horsepower information and be 100% accurate.*-

This statment is completly invers, torque curve determines HP, not HP determines torque, torque is an instantaneous measurement of the rotatonal force your motor is making, and is directly related to VE which this equation directly affects. Horsepower is a measurement of power, The equation for HP is: Torque * rpm / 5250, thus they are dependent upon each other, however any effect of the intake runner tunning would been seen in the VE of the motor at the point it is tuned for, and thus augment the torque curve. Refer to the image i posted, that is a graph of the R26b's torque output for different runner lengths of its Variable intake system, if the Manifold were tuned for 6500, you would see a curve arise around this RPM, if it wasnt tuned for 6500, you would expect torque to start falling off, Which would make the HP start to level off, and eventually decrease, exactly what we see on S4 dyno graphs. Also, the T2 makes peak power at 6500 RPM aswell, however its runners are longer, and tuned for a lower RPM than the NA's, I know there is a turbo involved, but it too is sized more around 2000-5000 rpm aswell. This equation relates to VE not peak HP(directly)

I have a RB Header sitting at my Dad's house, I'll measure the runners next tiem im over there.

drago86

Also I just wanted to say that the equation is excelent and 1300 is a very good all around average number to use for the speed of sound.

Also about the helmholtz, your saying they are using the air filter box as a resonator for the plenum then?

drago86

I'm not trying to start a fight or anything either, and i wasnt trying to flame you our anything when i was skeptical of the equation, i was just tryign to dbate it, and i have been proved wrogn a number of times in this thread, but ive learned alot also, so its great for me,..

Project84

.ppt is a power point file

rotarygod

iTrader: (1)

It's cool. We are all friends here! The T-II runners may or may not be exactly equal length but they are closer than the n/a's.

Yep, direct torque to horsepower relationship. If you transpose the horsepower curve to that chart you'll see that they did it perfectly and maximized each rpm. Of course you already knew this If you can find the exact specs of the engine and plug everything in, all of the peaks will probably perfectly line up with all of the calculated lengths. At the very least they will be close.

A turbo does some neat things with respect to tuning. An intake can be tuned to a certain powerband when it is on an n/a but when we add forced induction we can change this up. Different size turbos have different efficiency ranges. A big turbo may not hit its efficiency range until higher in the rpm range since there is not enough cfm flowing through it at lower rpms. When this happens, the turbo will continue to shove more air into the engine regardless of if the manifold is past its efficiency point or not. The turbo can theoretically continue to provide boost and hence more power higher and higher in the rpm range, regardless of manifold length, as long as it can stay in its efficiency range and keep supplying the air. This is why we can use a manifold with really long runners for great low end power when we are not on boost but still have good top end. The turbo overcomes the limitations of the manifold. Now imagine what would happen if you had the proper manifold on it! The above reason is why all kinds of weird port combos work great on turbo cars but terrible on n/a's On an n/a we are solely using the manifolds to build power whereas with forced induction we are doing just that, forcing it. FWIW the runners on the T-II tune the engine the exact same as the n/a's per their duration of port timing. If you run this car n/a you will have the same torque and horsepower peaks!

The speed of sound is actually closer to 1100 fps but for some strange reason when it is all calculated out, 1300 works better. I can't explain that one.

Yep, the Renesis airbox is a Helmholtz chamber. I use the term plenum liberally since a plenum is just a collection box for air. It doesn't have to be the actual "plenum" though. If you look at the stock 2nd gen air filter housing and look at the little tube coming off of it, this is a form of Helmholtz plenum too. It is just tuned very low and lacks flow. Removing this will give more power on that car but the area around 2000 rpm will suffer slightly. Who cares about 2000 rpm? Mazda does because they have to meet gas mileage expectations too. If we redesign this properly we can get a boost in the 6000 or 7000 rpm range. Nobody does this though. I don't know why. Helmholtz works by simply tuning a box to a certain frequency. The proper ratio that works the most efficiently will correspond with an intake tube (not runners) that has a large enough diameter that at peak rpm the velocity through it does not exceed 122.73 mph. Have fun with this one! As with the intake runners, its not saying we can't tune a smaller or larger chamber to the right spot and still get a gain. But, like runner diameter, there is only one combo that works the best. More technical stuff to digest! The power point presentation is 43 pages long. I have it printed up and installed in a notebook with all of my other notes and sources on the subject.

drago86

-*The speed of sound is actually closer to 1100 fps but for some strange reason when it is all calculated out, 1300 works better. I can't explain that one.*-

Speed of sound is highly dependent upon temp and humidity

http://www.measure.demon.co.uk/Acous...are/speed.html

We still need to find another source and see what the stock manifold was designed to be tuned too. Ive got the ppt downloaded, but i need to get a progie to read it.

drago86

also you forgot the 20-30 dregree subration fromt he duration, which insures the pressure wave arrives while the port is still open, this would only effect the tune by a few huECD = 720 - Adv. duration - 30 this would only effect the tune by a few hundred rpm however. The equation for ECD is: ECD = 720 - Adv. duration - 30

so the formula shoudl be: L= ( (1080-(EPD -30)) X 650 / (RPM X RV)

also this equation will NOT work even remotly for exaust with a constant of 650. Raising the temperature to 1400 degrees puts the speed of sound somewhere around 2100 ft/s, not to mention the high humidity, CO,Co2 content, and pressure, all which will raise the speed of sound even higher. To acuratly utilize this equation for exaust you would need an egt, a preessure sensor(measure the backpressure at the rpm your tunning for), a humidity sensor(yes cars make ALOT of water vapor) and if you really really wanted to do it right a complete anallysis of its gas content, and particle content. The etg, humidity and pressure sensor will get you close though, oh and did i mention that the equation to figure it out is like 3 lines long, with about a page of constants and equations for defining constants. Of course we can allways make an eduacated guess,..... id guess around 2700,.. but that could be WAY off. anyone here got a lab, and REALLY likes math?

mob

damn thats alot of math i didnt understand one bit of it, i got alot to learn lol

rotarygod

iTrader: (1)

The reason I didn't account for the 20-30 degrees where the ports are opening/closing is because it almost gets cancelled out by another factor, runner length within the housings themselves. One factor adds a few inches and the other one subtracts a few. They almost cancel each other out completely. The differences that I have been finding are only on the order of tenths to hundredths of an inch. Altitude and temperature will play a bigger factor than that. It would be best to build the manifold a tad on the short side, on the order of a half an inch or so, and then add a spacer on the dyno to properly tune it.

I did find the .6 mach number referrenced in an M.I.T. (Massachusetts Institute of Technology) textbook. (I wish I was smart enough to have gone there!!!) The book is called: The Internal-Combustion Engine in Theory and Practice Volume:1 Thermodynamics, Fluid Flow, Performance. It is a 574 page long textbook on the subject! There's even a second companion book! In chapter six, which is called: Air Capacity of Four-Stroke Engines, there is a part of the chapter that is called: Effect of Operating Conditions on Volumetric Efficiency. This section goes from page 171-187. The first subsection within this section is called: Inlet Mach Index. It goes through some math equations and charts and shows how efficiency is affected at different air speeds. They refer to these speeds within the runners as the Z value. On page 175 under the subsection: Maximum Z Value, the first sentence is: "From the foregoing results it is possible to draw the very important conclusion that engines should be designed, if possible, so that Z does not exceed 0.6 at the highest rated speed." Later in the book on page 419 there is a definition of 'rated speed'. "Rated speed: The rpm at rated power". So basically, in english, we should design our runner diameters so that at peak power rpm, the intake velocity should not exceed .6 mach. Now we have the number in writing somewhere so it is no longer a rumor! You may like this book. It is quite complex, very long, very technical, and has more formulas than many of us thought could have been possible let alone that deals with engines!

The temperature/air speed relationship seems backwards in my mind. I need to go think about that one for a while. (Yep, saw the link) Hmmm.....

Here is another quote from the book from page 432: "Volumetric efficiency is affected by the change in sound velocity caused by humidity changes. However, over the usual range, this effect is so small as to be negligible."

When we are tuning to a specific length we are tuning to a certain frequency wavelength. In other words the length of the runner will correspond to the length of a certain frequency wave. This wave at this frequency is the same length regardless of temperature or pressure. What temperature and pressure do effect though is the speed at which the wave moves. Imagine a limo moving at 2 different speeds down the highway. It is still the same length regardless of its speed. The same formula does apply to the exhaust. I know it seems strange and logic would dictate that a number in the formula changes, but it just isn't so. This is why I am a little confused as to why 1300 works better than 1100. Speed does affect the perception of a frequency change though. It is a very good question. I'll have to go do some more in depth reading to answer all the new questions that I just came up with. You like trying to stump me don't you!

I like that little calculator. Too bad it only goes from 32* to 86*F. It does get the point across though.

I like how you question every little aspect! You make me think of this in a far greater aspect than just the simple equations. Lets keep this going.

Zach McAfee

This is a very good thread. I'll read it all when I'm not at work.
Rotarygod, I know you were on another thread I was in where I posted an excel spreadsheet. Did you find the results from that accurate? It's on this page if you don't have it: http://www.zaxjax.com/intake_runner_...calculator.htm

rotarygod

iTrader: (1)

Zach, From what I have found, your spreadsheet is off. A port with a greater amount of timing will need a shorter runner to be tuned to the same rpm as that of a shorter duration port. Your spreadsheet seems to contradict that. Also, there should only be one answer for any rpm value in relation to any particular porting style. Some of your variables are not important in figuring out runner length. It was a valiant effort though! The variables that you do need to know are: peak power rpm, port open duration, speed of sound in fpm, reflective value desired, and runner diameter although this is only figured in AFTER the main equation is done. If you go back through the thread you'll see how and why it all works like it does and why intake runner velocity plays no part in this equation. drago86 brought up many good questions in the thread and hopefully my answers will shed some light on how it all adds up. If you get the chance, read the entire thread. Don't mistake anything for hostile responses.

For the half bridgeport, the reason that it doesn't pull very good with the stock intake manifold is an obvious problem. (I built one before too but it never right right. Wished I'd have known then what I do now). The secondary and the now bridged aux ports each require a different port length for optimium efficiency. Since they share a single runner, we tune for the aux port. The problem is that the secondary port is nowhere near its efficiency zone and you will have a couple of different tunings fighting each other in the same runner. You would need an extra set of runners like the Renesis does to function properly. The stock timing on the secondary ports for a power peak at the stock 6500 rpm, needs a runner that is 17.6" long. A bridged aux port needs a runner that is 9.2" long. The stock length is only 17.1" long. See the problem? The added timing lowered the usable power band a long way down! We are getting near a length however where the third reflection would assist some but not at the desired rpm. The VDI on the S5 manifold is not a problem here. It still functions perfectly at the desired rpm regardless of port timing. It is the runner length that is the serious issue.

Zach McAfee

Ok, I just messed up the timing thing. My calculated lengths increase with increased timing, silly me. I'm fixing it.
I think this is a stickworthy thread.

Edit: BTW, I used intake velocity to find the proper diameter of the runners. I'm sceptical about the results thought, since the calculated diameters are smaller than what I expected.

drago86

Yeah, the calculations get real real bad if you want to calculate the exact speed of sound, and the approximate formula they use is only good for that temp range. I understand the wavelength will not change, however the faster the sound wave moves, the shorter the header will have to be to have it return at the correct point. Some jetski's use water injection to tune the exhaust. The cooler you make the exhaust, the longer the pipe acts. 2 strokes are very sensitive to exhaust temperature because a properly designed divergent/convergant cone exaust often increases peak power by 100%, however if the exaust temp isnt maintained constantly the tne on the pipe shifts, and is no longer at the motors peak effeciency.

drago86

I also agree the stock NA LIM is a horrible design, ever notice how the LIM right before it is separated to the secondary/aux port has a larger cross sectonal area than the inlet to the LIM? Ive often thought about making a LIM that has separate runners for the aux ports, which rejoin the secondary runners at the right length, effectivly using the secondary runners as a plenum, which would be at high pressure after the secondary ports were closed.

drago86

Hey Rotarygod, since your GF is a math major, and you seem fairly adept at it aswell, may i PM you with a small math problem ive been struggling with for awhile?

also your right that the minus 20-30 degrees in the equation is neglidable, but if you wanted to tune for an exact rpm it should be included, and the runner length in the side plate should be included also, aswell as the -1/2 diameter to be exact.

Zach McAfee

This thread needs to stop until Rotarygod reads his PMs and gets back. There may be a problem with the theory from the start.

rotarygod

iTrader: (1)

Nope no problems on my side. This is how it works. It is extremely close. Close enough that anyone plugging in their timing specs can build a manifold that is just about right. Just build it a slight bit shorter and then add the appropriate spacer (phenolic? liquid anarchy!) on a dyno to get it exact. Your location and altitude will have the biggest effect. I've already built a manifold and am currently working on 2 others. One is for a 6 port and the other for a turbo. If I wasn't confident in the numbers I wouldn't waste my time and money designing them. It took a long time to fully understand how it all ties together and why it works the way it does. You hit a plateau of knowledge and understanding and stay there for a very long time. Then one day it just hits you and it all fits together. Sometimes completely opposite as to what you always believed. I used to think so different than what I do now and I swore by it, thinking that things couldn't possibly work any different. Its' a neat little wake up call when you learn what really happens. Lot's of math to understand and unfortunately the casual enthusiast won't understand it very quickly.

Yeah send me the math problem and I'll look at it.

Zach McAfee

Sorry, but I can't leave this one alone.
We have to understand the theory. We can't just apply equations.

This equation is based on the pulse created from a closed valve. The pulse is from the 'cramming' of high energy intake charge and the bounce back which is used for the next time the valve opens. In a piston engine.

This doesn't work for a rotary because there is no valve to close. Intake tuning is based on the pulse created by the opening of the port. The pulse is reflected and returns to the port before that face of the rotor closes the port.

When you subtract ECD from total timing you are finding how long the valve is closed. This is wrong!
Your numbers seem to match Mazda's final product, but the intake runner should be longer for increased open duration, since the pulse needs more time to arive at the port before it closes for that rotor face. With the piston engine equation, intake runners get shorter for increased ECD.

Can anyone else confirm this?!?! Can we get someone like Paul Yaw to tell us which one is right? We have two completely contradictory equations and two people who think each others methods are wrong.

rotarygod

iTrader: (1)

When you subtract ECD from the total you are not finding out how long the port is closed. You are finding out how long it is open. If you take the ECD number for the rotary and divide it by 3 (number of rotor faces) you have the actual timing open duration for 1 rotor face. So the equation calculates for all 3 faces being fed by 1 runner (or 2). You are still stuck on the acoustic side of things for a useful bounce wave returning to the other side. That is only one aspect in a design.

Zach McAfee

But according to you: "EPD= Effective Port Duration (how long they are open for)." So subtract how long they are open from the total and you get how long they are closed.

rotarygod

iTrader: (1)

Oops got me on that one. EPD calculates for the total open area of all 3 rotor faces combined. OK take the 1080-EPD number and divide it by 3 to see the total closed time between rotor faces. The intake manifold doesn't know if its attached to a rotary or a piston engine so why would it work any different? It doesn't. The formula automatically accounts for this. It is purely based on timing and has nothing to do with the returning pulse from the other rotor. Look at an individual runner system. I do understand the theory behind how it all works and quite well at that. That's how I know how to apply the way it works into a formula. You have to understand the engine before you can understand the math. The rotary is a 6 stroke engine you know!

Zach McAfee

First let me quote the theory my method is based on:
"The following facts are based on empirical knowledge, direct observation and published data.

After the intake port opens, a low pressure pulse is produced. This pulse propagates along the intake runner until it reaches the end (the end being the point where the diameter of the runner increases significantly) where it inverts and returns as a high pressure pulse.
The runner length should be set so that the returning pressure pulse coincides with the closing of the intake port."

Your formula is based on timing the pulse created by the intake valve closing.
My formula is based on timing the pulse created by intake valve opening.

What happens on PP intake ports that never close? What are you tuning then? You talk about reflections, but you never specify what causes the pulse.

It does matter what type of engine it is!

6 stroke engine? I don't know what you mean. It's a 4 stroke/4 cycle.

I've never mentioned the other rotor. My numbers are for one rotor, one face, one pulse, working off the amount of time the intake is open.

wanklin

iTrader: (2)

this needs to be a sticky.

rotarygod

iTrader: (1)

The return pulse with which you are referring to is the acoustic wave (since it travels at the speed of sound) which can either help or hurt the power of the other chambers. The biggest problem with mathematical formulas that predict proper intake runner length is that they do NOT account for the acoustic effects that take place within the manifold. The formulas do tune according to a certain length frequency wave in distance only (which varies based on timing) but they do not tune according to a return wave affecting the other chambers. Now I understand where you are coming from and from the acoustic side of things I concur with your observation. What would be interesting is to use your formula to predict where to put a VDI actuator. The problem with all engine based formulas is that they all only take one factor into consider to determine an answer. One formula is used for runner length based on timing. Another formula is used to determine plenum volume based on engine displacement. Another formula is used to determine runner diameter based on max rpm. Another formula is used to determine acoustic return waves. None of them takes into account the others. You get the idea. Unfortunately there is no single magic formula which tells everything.

To figure out the whole 6 stroke thing just look at how many times an eccentric shaft lobe goes up and down over the entire cycle of all 6 rotor faces over the complete 1080 degrees of rotation. 6! A 4 stroke engine does it in 4 and a 2 stroke does it in 2 granted they do it over 720*. Don't get this confused with the 4 internal cycles of intake, compression, ignition, exhaust.