IKnowNot'ing

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).

shelleys_man_06

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 .

shelleys_man_06

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 .

IKnowNot'ing

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!?

bgreene

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.

Reaper Man

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

zoom44

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.

rotarygod

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.

shelleys_man_06

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

rotarygod

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.

zoom44

seems like a trombone to me.

shelleys_man_06

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 . Here's a link that helped me define what Helmholtz resonance tuning is:

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

Reaper Man

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

IKnowNot'ing

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.

zoom44

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.

Japan8

Check this thread to see what the hell I was trying to get at....

wakeech

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.

Zaku-8

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

Japan8

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?

rotarygod

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 ***.

Japan8

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

rotarygod

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...

Japan8

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...