Ok so what is making those noises when you accellerate? the intake used on the RX-8 is called the Sequential Dynamic Air Iduction System or S-DAIS for short. it looks sort of like the diagram in the next post. what you hear at those rpms when the intake tracts open is a barrel shaped valve that is operated electronically turning inside the intake "tube" to open it's specific tract. the intake tracts open at specific rpms regardless of throttle position. althouigh i think, and i may be wrong on this point, that the VFAD- variable fresh air duct my be throttle position sensitive in relation to it's option of opening at 5500.

What happens when :
RPM___SYSTEM_______WHAT
3750__Fuel Injectors__#2 primary and secondary injector start
___________________controlled by ECU fuel maps
___________________(All in use during WOT!?!)
3750__SDAIS________#2 primary intake ports open
5500__SDAIS________VFAD may open (Yamaguchi p 115)
6250__SDAIS________Tertiary intake ports open
7250__SDAIS________Primary intake ports interconnnect
___________________adds a second shorter path
7250__SDAIS________VFAD opens on WOT

here is the Diagram:

http://www.rx8club.com/attachment.php?attachmentid=13884&stc=1

as was mentioned in the other thread that this spun off of, others have thought the intake opening sounds were "pinging" or "bearings". for instance in this thread www.rx8club.com/showthread.php?s=&postid=260674&highlight=intake#post260674

next perhaps rotarygod and/or others can step in here and explain a little about Resonance Tuning in the Renesis.

My question around that idea and talk about the intake - as you see on the top of the diagram there is a valve> that valve as I saw in some video is just outside the air intake... as the wavy lines below that is the air box (I suppose)...

when we do intake - which got rid of the box.... won't we just let it all open????

If the answer is yes then... do we tune the ECU/piggyback to make it better...

THANK YOU VERY MUCH TO THE ANSWER IN ADVANCE.

Taka

Here's all you ever wanted to know about the RX-8 intake.

Aftermarket intakes only do away with VFAD. No there is no ecu retuning to account for this. There are gains (very small) though but they are based on total airflow vs resonant tuning. Somone needs to make a resonant tuned intake that flows good too. This would yield bigger gains that ANYONE else's intake system out there. I've said it here for almost a year now and still no one has done it.

I am not sure but I should at least hope that each valve and VFAD open at a set rpm regardless of load. Tuning is rpm based not load based. This would make the most sense.

If you look at the diagram very carefully you can see how everything works. The wavy lines are the air filter in the airbox. This set of diagrams is the 6 port engine. There is also one of the 4 port engine but not pictured here. It is very similar but lacks 2 intake ports and the VFAD duct on the intake.

Below 3750 rpm, only the primary (2 center ports) are receiving air. This insures that all of the airflow going into the engine is at a high velocity unlike the older rotaries where all of the ports were open at the same time. Mazda tried to overcome this problem with a 3 plate throttlebody and only opening the primary plate alone unit 20% throttle. It is a little complicated and I don't want to explain it all here. Let's just say this (Renesis) is superior.

At 3750 rpm when airflow is at its greatest and is starting to hurt power (intake airspeed around .6 mach), the secondary ports open up. Obviously this is why the fuel injectors are fired sequentially so there is no fuel in a nonmoving runner. Now we have a total of 4 ports being used until 6250 rpm. This again becomes a flow restriction and the tertiary ports open up.

At 7250 rpm the VDI (Variable Dynamic Intake as known on the 2nd gen RX-7) valve opens up which retunes the intake for higher rpm use. I'll explain it in a minute. Also at 7250 rpm the VFAD duct on the intake box opens up. This does a couple of things. It does allow a shorter more direct route for air to enter but that is really a moot point. More importantly it retunes the intake box. The stock airbox size along with the intake duct's length and width combine to acoustically tune the airbox to resonate at a certain frequency. This frequency is set to help the engine gain power at lower rpms. When the VFAD duct opens, it is retuning the intake box and adding its own area to the available area for air to flow through. It does a pretty good job considering that it is only a few horsepower less than the aftermarket cone filter systems but has the capability for way less ariflow. The total area for air to enter the stock box is less than the area of either the throttlebody or the MAF sensor. If Mazda would have given it a little more intake area with the same tuning, the aftermarket probably would have never outdone it. If you want to figure out the perfect size for the intake tube, figure out the diameter necessary for air entering the box at 8500 rpms to not exceed 122.74 mph. That will be the optimum size. Length will be determined based on tuning rpm and intake box size. There is a fun exercise for someone.

Back to the subject of VDI. The reason this valve opens is to retune the intake manifold so the engine thinks the runners are shorter. I've posted this before but here it is again. The intake runner lengths are determined by what rpm the designers want a gain to be at. The continuously variable intake runner length as on the LeMans 787B car is not feasible in a streetcar but we can partially simulate the effects. When VDI opens, the pulses from one rotor do not have to go back to a central point before heading back down the opposite runner to either help or hurt it. In essence when the VDI valve is open, the engine only "sees" the runner up to the valve and not after (before depending on your frame of reference) it. Here's the effective lengths.

6 port "effective" intake runner lengths.

Primary VDI closed 19.8"
Secondary VDI closed 20.4"

Primary VDI open 13.5"
Secondary VDI open 14.2"

Tertiary always 17.3" VDI does not effect these runners.

4 port "effective" intake runner lengths.

Primary VDI closed 27.1"
Secondary VDI closed 29.1"

Primary VDI open 14.8"
Secondary VDI open 16.5"

As you can see when the valve opens it is like installing a shorter intake manifold which retunes for better high end power. The real black art is designing an entire system that works together almost seemlessly. Mazda did a very good job on this intake manifold. It is much better than anything they have ever done and most likely will be very tough to improve upon without some big sacrifices elsewhere in the powerband.


The dips in power as seen on the dyno are the valves opening. The problem isn't so much that there is a pressure drop causing the dips but rather than the valves don't open quick enough. They are not electrically opened as other here have stated. They are opened pneumatically. The electric confusion comes from the fact that there is a solenoid that electrically opens at a set rpm that allows air to flow to the actuators which causes them to open. If a reliable servo could be found, it would be a better system. The faster the better.

I forgot to mention another length difference between the 4 and 6 port engines. The intake duct going into the airbox is not the same between both engines. The 4 port engine does not just use the long pipe from the 6 port engine. It uses a longer pipe. Obviously it does not have the VFAD duct either. Different engine require different tunings.

I wonder if I forgot anything else?

thansk for the input. i thought about just quoting some of your posts from prvious discussions but wanted to give you a chance to way in here. you have put it together very neatly. thanks again rotarygod!

I have a related question and I would like to know if anyone else is experiencing the same thing...between 3200-3700 RPM when I'm accelerating, regardless of how hard, I hear a rasping or rattling sound coming from under the hood.
The Dealer also heard it when I took it in for an oil change. They didn't have time to get into it since I couldn't leave it. I first thought this may have been noise from the other intake runners opening up but according to the above posts it sounds like it's too early in the rpm band. Could it be misfiring? Is this normal? Does anyone else have the same sounds? (You'd know if you did) Would the "L" flash help fix this if it is detonation?

Almost, Mr. God,
The air shutter valve, up front, IS a vacuum flap, operated by a solenoid signal, but the Auxiliary port 'barrel valves' are MOTOR operated.

S

sorry for the crappy scan....

Oh God... so are you saying that it is not worth JUST putting a "mushroom" (CAI) in with out anything like a Turbo or S/C or has a ECU retune wtih a piggyback?

Originally posted by StealthTL
Almost, Mr. God,
The air shutter valve, up front, IS a vacuum flap, operated by a solenoid signal, but the Auxiliary port 'barrel valves' are MOTOR operated.

S

sorry for the crappy scan....

Mr. God! ROFL!!!

Here is a picture of the lower Renesis manifold. The secondary runners and the VDI valve are vacuum actuators. Judging by the gears it does appear that only the auxillary valves are operated with a motor. I don't want to use a motor to spin like Mazda did but rather an electric actuator that moves back and forth instantly. Mazda didn't do this anywhere.

Originally posted by takahashi
Oh God... so are you saying that it is not worth JUST putting a "mushroom" (CAI) in with out anything like a Turbo or S/C or has a ECU retune wtih a piggyback?

If the only mod you are going to do to the car is nothing more than an intake, don't waste your time. You won't feel it. Yes there are small gains but they are not big enough to notice on their own. If you are going to do other mods then there will be a cumulative gain. If you do decide to do only an intake, it will be more for sound and looks than any gain in acceleration.

Originally posted by rotarygod
Somone needs to make a resonant tuned intake that flows good too. This would yield bigger gains that ANYONE else's intake system out there. I've said it here for almost a year now and still no one has done it.


AEM is working on an intake here:
http://www.rx8club.com/showthread.php?s=&threadid=22992&highlight=aem+intake

And I have a hunch, based on their V2 history, they are doing excatly what you asked for...:cool:

Originally posted by shaunv74
Could it be misfiring? Is this normal? Does anyone else have the same sounds? (You'd know if you did) Would the "L" flash help fix this if it is detonation?

from your description i cant tell what it is you are hearing. however if it is a misfire or detonation a code would be stored for these events and your service person will see them.

Fudging through the translation, Greddy's new intake is supposed to be tuned to some extent -

http://www.trust-power.com/mazda/rx8/gracer/airinx_b.html

From what I can tell, it's supposed to be better than a regular cone intake, but I can't tell if it still uses some sort of actuator, or they just have a tuned length/size for the intake.

Dale

Greddy has what I would consider the best alternative currently out there. It's size and length should give the car more usable power lower in the powerband than the others out there. It probably doesn't do much for ultimate top end but we don't all drive there anyways. It does not have an actuator at all. Just really long.

An unnamed but respected person on the forum here has claimed that the MAF would get bad readings because the air has too much velocity in this format. Doesn't the air have high velocity at high rpm's anyways? I find this to be a poor excuse against this intake.

Several people here have commented about how worried they are of sucking up water through the intake. It is nearly impossible without purposely driving through a flood as it would take about 90% of the filter being submerged for a period of time along with high rpms for this to happen. Someone has to be really careless to drive through water that high. My little Honda has a filter this low and I have never had a problem.

Thanks. I'll have to ask them to take a look at it when I bring it in next. It sounds like a rattle that comes on at a specific rpm range for a specific duration under acceleration. If the computer stores a code then they'll find it easily enough.

Thanks '44.

Now that I am off the ceiling from my engine ordeal. Thanks for the info on the intake system Zoom44. The new engine seems to run better now that I have run a couple of tanks of gas in it.I still get that noise/ping but only about 10 to 20 percent of the time. do you think it could have been gas problems? Is there a learning time in the computer because they gave me the L flash with the new engine. It is much better now than last week.

[QUOTE]"I have a related question and I would like to know if anyone else is experiencing the same thing...between 3200-3700 RPM when I'm accelerating, regardless of how hard, I hear a rasping or rattling sound coming from under the hood.
The Dealer also heard it when I took it in for an oil change. They didn't have time to get into it since I couldn't leave it. I first thought this may have been noise from the other intake runners opening up but according to the above posts it sounds like it's too early in the rpm band. Could it be misfiring? Is this normal? Does anyone else have the same sounds? (You'd know if you did) Would the "L" flash help fix this if it is detonation?"

I experienced somethig that sounds a bit like this. I would hear the noise in the lower RPMs and when I was decelerating. To me it sounded like it was coming from the transmission. Upon further investigation I ruled this out by simply having some one rev the motor while I stood outside the car. We realized it was coming from the exhaust and not the trans. I thought it might be gravel or something. Anyway, I dropped the car of at dealer to have them fix it and was suprised to hear that I had somehow blown out the catylst from the catalytic converter. The only explanation I can think of, short of a faulty catalytic converter, is that when I drove through a rather deep and long puddle the other night the rapid cooling on the outside followed by my rapid acceleration some how cracked the catalyst and then blew it into the exaust pipe. If anyone else has a theory or a similar experience, please share.

just figured out how to use the quote feature correctly.

Originally posted by Topgun
Now that I am off the ceiling from my engine ordeal. Thanks for the info on the intake system Zoom44. The new engine seems to run better now that I have run a couple of tanks of gas in it.I still get that noise/ping but only about 10 to 20 percent of the time. do you think it could have been gas problems? Is there a learning time in the computer because they gave me the L flash with the new engine. It is much better now than last week.

hey TOP nice to see you again. glad the new engine is working out better. the PCM does need to go thru a learning period so that could easily be it. the seals are probably seting and the engine is geting used to you. it's basically breaking in all over again. and like i mentioned earlier in this thread even if it doesn't light the cel, if the engine has knock/ping/detonation or misfires the ecu will store a code. i think they call it a soft code because it takes several to light the cell. so the next time you are in they can pull and read the codes if there are any. but the pcm will try to adjust timing to get rid of the situation hence the learning.

I have the raspy / rattling sound as well. I think mine is related to the crack-able (cracked?) housing above the tranny. I haven't taken it in for the recall yet, but when I do I'll tell them about it and see if any codes are stored.

OOH I STARTED A STICKY!! WOOHOO!!

Ok, what is a "STICKY"

I have to agree with you, rotarygod, the concern for sucking in water thru the CAI type intake is way overblown.

I'm pretty sure it is an urban myth, everyone knows someone who's 'friend' went thru a little puddle and blew the heads off their WRX/civic/Evo (whatever).

This scenario doesn't 'hold water' if you do the math - revs/water depth/amount per cylinder/vacuum required to lift water head etc.
Probably just perpetuated by the vendors of those 'foam-anti-suck' valves....don't get me started!

Also, this thread has got this far without mentioning the word 'Helmholtz'. This is not allowed. Don't ask me, it is one of Wakeech's rules.
.
.
.
doc

it means someone thought this was useful enough info to keep it stuck at the top of the page. it wont get buried by new threads until it is "unstickied". i dont start many of those ;)

Originally posted by Doctorr
I
Also, this thread has got this far without mentioning the word 'Helmholtz'. This is not allowed. Don't ask me, it is one of Wakeech's rules.
.
.
.
doc

agreed on the sucking water myth. but i did give rotarygod the chance at saying "Helmholtz" by defering to him when mentioning resonance tuning. apparently he decided NOT to take advantage of the oppurtunity, so the wrath of wakeech be upon him;)

Originally posted by zoom44
OOH I STARTED A STICKY!! WOOHOO!!

;)

Originally posted by Doctorr
I have to agree with you, rotarygod, the concern for sucking in water thru the CAI type intake is way overblown.

I'm pretty sure it is an urban myth, everyone knows someone who's 'friend' went thru a little puddle and blew the heads off their WRX/civic/Evo (whatever).

This scenario doesn't 'hold water' if you do the math - revs/water depth/amount per cylinder/vacuum required to lift water head etc.
Probably just perpetuated by the vendors of those 'foam-anti-suck' valves....don't get me started!

Also, this thread has got this far without mentioning the word 'Helmholtz'. This is not allowed. Don't ask me, it is one of Wakeech's rules.
.
.
.
doc

I do have a friend that sucked in water in her Z28 from a cold air intake. She was also dumb enough to follow a truck through a foot and a half deep of flood water.

I started the Helmholtz thread a year ago. It's funny how it still gets mentioned. I don't really need to post anymore on it. It would be a redundant book.

If Hermann only knew we would use his math for something other than accoustics...

It is still dealing with acoustics.

Originally posted by rotarygod
Several people here have commented about how worried they are of sucking up water through the intake. It is nearly impossible without purposely driving through a flood as it would take about 90% of the filter being submerged for a period of time along with high rpms for this to happen. Someone has to be really careless to drive through water that high. My little Honda has a filter this low and I have never had a problem.

I did it in a 94 T-bird. Careless, nope, it was a flash flood that came up to just below the top of the hood in less than 30 seconds as I was driving at about 30 mph down a street that normally does not flood. Sucked plenty of water in. Result was some nicely bent rods.

It does happen.

If the water level gets up to the hood, it doesn't matter where the air filter is at that point. You're still getting flooded. What I am referring to is people who have low filters who are afraid that a little splash from rain water or the ditch is going to kill their engine. It isn't. As I said earlier, you have to drive through a flood to hurt it. This you have proved.

Originally posted by rotarygod
If the water level gets up to the hood, it doesn't matter where the air filter is at that point. You're still getting flooded. What I am referring to is people who have low filters who are afraid that a little splash from rain water or the ditch is going to kill their engine. It isn't. As I said earlier, you have to drive through a flood to hurt it. This you have proved.

To that I can definitly agree. A little splash from rain or from running over a puddle in the road will not kill the engine.

From personal experience, it takes a LOT of water. A good way to tell if there is enough water to cause a problem is to check the seat of your pants. If they are wet, you may have a problem.;)

Sure was a good thing that a fire engine came up behind me and pushed me to higher ground, that water was moving fast.

The total area for air to enter the stock box is less than the area of either the throttlebody or the MAF sensor. If Mazda would have given it a little more intake area with the same tuning, the aftermarket probably would have never outdone it.


Now I get to say it.. :D I posted about this recently in another thread. In the review of the changes made on the Mazdaspeed RX-8, changes to the size of the VFAD ducts is one. Mazda's goal with the MS RX-8 wasn't to tune for ultimate horsepower. They were tuning for more "reliable" power... power on tap easily throughout the rev range. I suppose another way to say it is an increase in driveablility.

So what's my suggestion for RB and anyone else for an intake? Work on the VFAD diameter and length. If you want to look cool too... have that feed into a heat sheilded box (not just aluminum box, but add insulation/sound deadening material) with a cone filter. I think this will achieve the goal of a fair power increase without the crazy noise and idling problems of the K&N Typhoon.


If you want to figure out the perfect size for the intake tube, figure out the diameter necessary for air entering the box at 8500 rpms to not exceed 122.74 mph. That will be the optimum size. Length will be determined based on tuning rpm and intake box size. There is a fun exercise for someone.


Indeed. I hate math, so I won't be doing those calculations.

BTW, GReddy claims that their intake is resonance tuned to increase mid-range power. We'll see how that is once people can get their hands on it and give it a whirl.

Now I get to say it.. :D I posted about this recently in another thread. In the review of the changes made on the Mazdaspeed RX-8, changes to the size of the VFAD ducts is one. Mazda's goal with the MS RX-8 wasn't to tune for ultimate horsepower. They were tuning for more "reliable" power... power on tap easily throughout the rev range. I suppose another way to say it is an increase in driveablility.

So what's my suggestion for RB and anyone else for an intake? Work on the VFAD diameter and length. If you want to look cool too... have that feed into a heat sheilded box (not just aluminum box, but add insulation/sound deadening material) with a cone filter. I think this will achieve the goal of a fair power increase without the crazy noise and idling problems of the K&N Typhoon.



Indeed. I hate math, so I won't be doing those calculations.

BTW, GReddy claims that their intake is resonance tuned to increase mid-range power. We'll see how that is once people can get their hands on it and give it a whirl.

I have the SR Intake, and I wonder if it's length and diameter were calculated to match this??

What effect would forced induction have on S-DAIS? I am assuming you would have to change the time at which each valve opens. Since the valves are vacuum-regulated, wouldn't they adjust to the pressure rise in the intake stream, or is the valve actuation independent of pressure changes? I think Mazda chose vacuums because electronics would make the car unaffordale. Is it possible to switch from vacuum modulation to eletronic control, such as using a stand-alone EMS to do so? After all of the thinking I've been doing about forced induction, I forgot about the intake tract :o.

I would set it up so that under boost, all valves are open. When not under boost, it would work normally. The VFAD duct would no longer be needed. This would be very easy to setup. The hard part is setting up an ecu to switch maps based on boost or no boost.

What effect would forced induction have on S-DAIS? I am assuming you would have to change the time at which each valve opens. Since the valves are vacuum-regulated, wouldn't they adjust to the pressure rise in the intake stream, or is the valve actuation independent of pressure changes? I think Mazda chose vacuums because electronics would make the car unaffordale. Is it possible to switch from vacuum modulation to eletronic control, such as using a stand-alone EMS to do so? After all of the thinking I've been doing about forced induction, I forgot about the intake tract :o.

that sounds like an even more costly endeavor than having a new manifold fabbed up for your turbo system (which would then give you more flexibility in the design of the system, and better boosted performance).

all you gotta worry about actuating is the tertiary port, and just have six runners at a tuned length to the engine from one plenum designed to resonate at X rpm.
i dunno, instead of complecating things even more, i move to simplify things a lot.

What effect would forced induction have on S-DAIS? I am assuming you would have to change the time at which each valve opens. Since the valves are vacuum-regulated, wouldn't they adjust to the pressure rise in the intake stream, or is the valve actuation independent of pressure changes? I think Mazda chose vacuums because electronics would make the car unaffordale. Is it possible to switch from vacuum modulation to eletronic control, such as using a stand-alone EMS to do so? After all of the thinking I've been doing about forced induction, I forgot about the intake tract :o.

that sounds like an even more costly endeavor than having a new manifold fabbed up for your turbo system (which would then give you more flexibility in the design of the system, and better boosted performance).

all you gotta worry about actuating is the tertiary port, and just have six runners at a tuned length (you could choose to go either with a comprimise setup where the runner to each port resonates at a different velocity and has a different diameter, or the full-out performance setup where they all resonate at one rpm and are of a larger diameter) to the engine from one plenum designed to resonate at X rpm.
i dunno, instead of complecating things even more, i move to simplify things a lot.

wakeech, rotarygod, I found some of your old threads about making power with the RENESIS. Why did they die off?

Zoom44, (or any of the other more 'techie minded' people here)

Is the data you gave at the very beginning of this thread only applicable to the MT or does it apply to the AT too? Or, did they change at what rpm things occur to take into account the lower available rpm to the AT owner?

(Sorry if this is both a dumb and obvious question... but I'm curious given I own both an MT and AT and am trying to learn as much as I can about the tech side of these cars..)

Zoom44, (or any of the other more 'techie minded' people here)

Is the data you gave at the very beginning of this thread only applicable to the MT or does it apply to the AT too? Or, did they change at what rpm things occur to take into account the lower available rpm to the AT owner?

I think that diagram only applies to the high-power (6 M/T in the United States) RENESIS. I do not think that the AT is VFAD-equipped.

rotarygod had a thread a while back explaining the 4-port RENESIS. Try a search :). It might help solve your question.

Yep, the auto does not have the VFAD duct or the tertiary ports. the rest it does have. The lengths of the intake runners is different though and even the VFAD duct is longer. The principles are the same between both engines. The auto just has less of everything.

Shelleys_man_06 has got it right. The A/T has the 4 port engine instead of the 6 port engine. The two engines are quite different with the 4 port motor lacking auxiliary ports and the port timing is different. To simplify the explanation that RG gave in another thread... the 4 port motor simply cannot "breathe" as well as the 6 port motor. However, as RG has pointed out... the intake system is still a resonance tuned system... just one built to flow less.

Wakeech has often said that the 4 port motor is a better FI candidate than the 6 port. RG has argued the opposite. The Renesis engine with the side port "can be set to less than 0 overlap" according to Seiji Tashima, Mazda lead rotary engineer.was built essentially without port overlap (if I understand my JP article correctly). This is how it make better emissions. This also has an effect upon how good it is for FI. RG would need to jump in to explain this better, but apparantly some port overlap is good for turbo applications.

Zoom44, (or any of the other more 'techie minded' people here)




wow i got included with the "techie minded" people here!! not sarcasm here- that is a great honor for me to be included in that group. thank you :o :cool:

wakeech, rotarygod, I found some of your old threads about making power with the RENESIS. Why did they die off?

'cause there ain't so many people interested in discussing these things.

Here's all you ever wanted to know about the RX-8 intake.

....


If you want to figure out the perfect size for the intake tube, figure out the diameter necessary for air entering the box at 8500 rpms to not exceed 122.74 mph. That will be the optimum size. Length will be determined based on tuning rpm and intake box size. There is a fun exercise for someone.

...
I wonder if I forgot anything else?

EXCELLENT summary, thanks. Can you however explain where does the 122,74 mph optimal speed for intake air come from?


Re some other posts in this thread : water ingestion through the intake pipe (spout) is definitely not an urban myth. The intake pipe had to be redesign on the Escape / Tribute program before production due to this issue of water ingestion!
Now, it means that car manufacturers carefully check their intake systems against this issue and it should not be an issue any more on your production vehicle.

IKN, I believe if the velocity exceeds 122.74 mph, the flow losses through the intake will dramatically increase. Why *shrugs shoulders* ? If I am wrong, which in most cases I am :(, I am sure rotarygod would be more than happy to make any corrections, because I am starting to wonder the same.

EXCELLENT summary, thanks. Can you however explain where does the 122,74 mph optimal speed for intake air come from?


this may have been a mathematically derived number (backwards from all the known meausurements), but theoretically it would be a speed where at maximum engine speed (WOT, of course) the comprimise was such that velocity could still be maintained at lower engine speeds (where marginal efficiency loss at some point in the higher end equals the marginal efficiency loss at some point in the lower range). the "terminal velocity" would change based on the shape of the path to the engine, and the surface over which all that air was travelling, not to mention the kind of comprimise you're trying to strike in the design.

i'm not sure how he came up with that number, though, as it's far less than half the speed of sound (some arbitrary number i read once on an F1 tech forum).

IKN, I believe if the velocity exceeds 122.74 mph, the flow losses through the intake will dramatically increase. Why *shrugs shoulders* ? If I am wrong, which in most cases I am :(, I am sure rotarygod would be more than happy to make any corrections, because I am starting to wonder the same.

Again, you might be right. Perhaps, considering the Renesis intake system runner diameters or main pipe diameter, incoming flow becomes turbulent around that speed. I haven't got the pipe dias, so I cannot verify if this is the source for the 122 mph figure.
Or does it have a connection with the speed where the flow through the inlet valve becomes chocked (i.e. reaches sonic velocity)? I don't know (yet).

Actually, the velocity may come from manipulation of the, ugh, Ideal Gas Law, which has a mass flow rate form. I won't go through the tedious calculation, but that velocity probably comes from the manipulation of the pressure, temperature, and area of the pipe. Of course, this is in steady-state form; the air passing through the intake tubes is transient, so it would be a good idea to account for it. In short, I believe there are too many parameters do truly decipher this number. IMO, I would just accept this as a given; we might be able to use 122.74 mph as a reference point for maximizing the abilities of the RENESIS :).

In addition, wherever this number came from, I believe that Mazda's intention was to keep low-speed driveability. Air velocity is good, but when you reach the choke point, or I suppose sonic velocity (?!?), airflow has reached its peak. Since this is the real world, the airflow may not stay constant when choked. Transient response tells me that the airflow will eventually subside with time, or should I say, mass airflow after the choke point will decrease. This inadvertent change may cause dramatic flow losses, which ultimately leads to power loss. Only by increasing the area, temperature, and pressure, that we may exceed 122.75 mph without a chance of power loss. My head hurts :(.

this may have been a mathematically derived number (backwards from all the known meausurements), but theoretically it would be a speed where at maximum engine speed (WOT, of course) the comprimise was such that velocity could still be maintained at lower engine speeds (where marginal efficiency loss at some point in the higher end equals the marginal efficiency loss at some point in the lower range). the "terminal velocity" would change based on the shape of the path to the engine, and the surface over which all that air was travelling, not to mention the kind of comprimise you're trying to strike in the design.

i'm not sure how he came up with that number, though, as it's far less than half the speed of sound (some arbitrary number i read once on an F1 tech forum).

Oops, didn't see your post at first. Your explanation confuses me. I believed the S-DAIS take care of optimising flow (and velocity) across the RPM range...
This number, with 2 decimals !!, must definitely come from a formula / calculation of some sort. And indeed is far below the 0.5 Mach that is used as a rule of thumb.
However, this 122 mph air speed at the air box inlet might correspond with Mach 0.5 in the different S-DAIS runners though reduction in overall cross section!?

Does anyone remember the formula for Reynolds number? That might be the key, check the Reynolds value at that critical speed for the length of the longest runner. That'll give some idea of whether you're looking at laminar/turbulent flow at the intake ports (although all the twists, valves and forks in the intake manifold might complicate that some).

It could be though that you'd want turbulent flow at the injectors, or a short area of turbulence between the injectors and the ports, as turbulent flow might make for better fuel/air mixing, which might in turn improve combustion efficiency of the mixture.


On a separate note, I did the calcs for the theoretical intake area:

using constants,
Vcrit = 122.74 mph = 2160 in/s
Disp = 1.3 L = 79.3 cu in
Redline = 8500 RPM = 141.7 Hz

It's a pretty simple calc;

A(intake) = (Redline * Disp) / Vcrit

so,

A = 5.20 sq in. (this corresponds to a tube with a radius of 1.29 in)

I'd imagine that with all 6 ports open, the sum of the runners can make this area, and the upper manifold looks like it's probably sufficient. I may need to take a look at my factory airbox, though 'cause I'm not sure if the duct in from the VFAD looked big enough to make this much area.

question- would a S-Dais malfunction cause the car to "not exactly" rev passed 6k- about where it activates?

a stuck valve could cause some "stumbling". the turbulence casued by it openign at that part causes a little drop in power until the airflow recovers. but also when the engine is cold the pcm keeps an electronic rev limiter at @6000 rpm until the engine gets up to a certain temp.

First of all the 122.74 mph number ONLY applies to Helmholtz resonant tuning. If we designed a new airbox, the diameter of the intake tube would need to correspond to this number at our desired power peak. The intake manifold itself does not use Helmholtz resonant tuning, just the intake. That number is also only assuming you want the most efficient diameter of pipe. It is not the only size that will work. It just corresponds to the point of max efficiency.

The intake runners actually want a much higher speed of .6 mach. That is somewhere around 450 mph. Big difference. You are fine below this but don't go above it.

So, tuning the air intake tube is just a matter of acoustics, rather than by manipulating temperature, pressure, etc.?

It is determined by the size of the airbox vs. the length and area of the tube feeding it. Just envision a ported speakerbox with the engine side being the speaker.

seems like a trombone to me.

Thank you rotarygod for the explanation. I did some mini-research on Helmholtz resonance tuning about 30 minutes ago. That makes more sense than my thermodynamics gobbledygook :confused:. Here's a link that helped me define what Helmholtz resonance tuning is:

http://www.phys.unsw.edu.au/~jw/Helmholtz.html

a stuck valve could cause some "stumbling". the turbulence casued by it openign at that part causes a little drop in power until the airflow recovers. but also when the engine is cold the pcm keeps an electronic rev limiter at @6000 rpm until the engine gets up to a certain temp.

the car is completely warmed up when it does it. it does stumble, but I'm thinking through my other research that it's my coils. Just wanted to throw a theory out to you guys that are far more knowledgable about it than I- to me, the rotary works from black magic

First of all the 122.74 mph number ONLY applies to Helmholtz resonant tuning. If we designed a new airbox, the diameter of the intake tube would need to correspond to this number at our desired power peak. ....

Yes, but why 122.74 mph? Where does that figure come from?

EDIT : after 10 min search on Google, I found a document where they mention 180 ft/s (= 122.74 mph), but again, without telling why and how they got that number.

the car is completely warmed up when it does it. it does stumble, but I'm thinking through my other research that it's my coils. Just wanted to throw a theory out to you guys that are far more knowledgable about it than I- to me, the rotary works from black magic


are you on the M flash? quoting from MSP04-
"Engine has lack of acceleration power and/or knocking when driving at more than approx. 6000 rpm or at high altitudes. This is caused by poor combustion gas sealing due to the lack of the amount of oil supplied byt the oil metering pump."

so it sound salot like what you experience. if you already have the M i suggest you show them that part of it anyway and get them to check out the oil metering system on your car.

Shelleys_man_06 has got it right. The A/T has the 4 port engine instead of the 6 port engine. The two engines are quite different with the 4 port motor lacking auxiliary ports and the port timing is different. To simplify the explanation that RG gave in another thread... the 4 port motor simply cannot "breathe" as well as the 6 port motor. However, as RG has pointed out... the intake system is still a resonance tuned system... just one built to flow less.

Wakeech has often said that the 4 port motor is a better FI candidate than the 6 port. RG has argued the opposite. The Renesis engine with the side port "can be set to less than 0 overlap" according to Seiji Tashima, Mazda lead rotary engineer.was built essentially without port overlap (if I understand my JP article correctly). This is how it make better emissions. This also has an effect upon how good it is for FI. RG would need to jump in to explain this better, but apparantly some port overlap is good for turbo applications.

Check this (http://www.rx8club.com/showthread.php?t=4372&page=2) thread to see what the hell I was trying to get at....

Wakeech has often said that the 4 port motor is a better FI candidate than the 6 port. RG has argued the opposite. The Renesis engine with the side port "can be set to less than 0 overlap" according to Seiji Tashima, Mazda lead rotary engineer.

well yeah, as you put in that same thread the exhaust closes at 3*BTDC and intake opens at 3*ATDC, so there's 6* of e-shaft rotation where there isn't a port open (called dwell): you can't get the intake and exhaust cycles more separated than that.

i'm really not sure how you could overlap the cycles, 'cause there isn'ta lot of metal between the edge of either the intake or exhaust port and the rotor housing, so i don't know if a bridgeport would be possible, or even a good thing. i'm quite sure that you cna't just extend the edge of the port out much more than maybe a whole 1mm (probably not even that much) before you'll just have your corner seal fall out of place, and just fuxor everything.

my "rattle" is at exactly the 3250-3500 region, for the whole duration... i dont see a corresponding SDAIS valve opening. Is there something else in the intake that is operating at that range

Horrible thread revival (I'm on a roll today)... but I was thinking about more NA power and less FI. BMW (racecars and motorcycles too) uses 1 throttle per cylinder on the M3 and M5. No value in dumping most of the S-DAIS and VFAD in favor of this? Better response? Even with a good port job and tuning?

I've actually thought that it would be neat to adaprt a 3 barrel weber style throttlebody as used on Porsche race cars. One throttle plates feeds the rear rotor, 1 feeds the front, and the last one feeds tha auxillary ports. It would need a new ecu though. Not sure how well it would work but it would look kick ass.

mmm... sounds like it would look badass! Another one of your "projects"? :D

Nope. Just an idea. Currently I'm working on the exhaust side of the car. I've done some airflow testing on my muffler design and the idea works as predicted on the mockup unit. I need to build a real prototype now to see if it looks good on te flowbench in relation to other muffler designs. Then I need to see if it will muffle worth a damn. That's where my fun has been lately.

I'm waiting on my CAD drawing of the exhaust flange for the Renesis right now. I'm not good with CAD but I have a friend who is. He's got 2 drawings coming to me that both will be sent to the machine shop to get cut out. After the flanges are cut out, then I can start mocking up my header idea. Who knows if that will work either. I am also going to build a generic turbo manifold for the Renesis since no one offers one yet.

This is all going slow though so don't expect to see any of this next week. I am also waiting on my new Renesis to arrive and this will take up alot of time since I am going to do alot of study on flow through it. All I need now is time...

And you're selling expensive property... quite the busy man.

I can't wait to see your results... especially the flow bench tested porting. I am also really curious how porting will affect the gains made by headers and cat-backs...