Measured Mass Air Flow & Efficiency
 

After reading some of Richard Pauls material, I decided I would take some of my actual measurements, and plot them.

I have used my own ODBII logging s/w and a CAN interface I aquired. I logged the MAF values (grams per second) against the measured RPM. (All measurements taken in real time from the PCM via OBDII).

I also plotted the Theoretical mass air flow, and calculate a % efficiency. At a couple of spots this is slightly greater than 100%. My reaction to this is the SDIAS in operation.

http://www.hymee.com/rx8/images/Mass...ciency_RX8.png

Notes:[list=1][*]MAF & RPM are actual as reported by OBDII.[*]Measurements taken at ~20 degrees C and 102 kPa BARO, virtually at sea level.[*]Theoretic displacement = 1.3 litres per revolution.[*]Theoretic mass flow calculated at 1.3 grams / litre (mass of air at sea level)[/list=1]

Thought it was interesting, and thought y'all might like to take a peek. I guess the actual displacement is acctually 1.308 litres, so I am out a tinsy bit, but you get the drift.

Hope you like it.

Cheers,
Hymee.

PS - Let me know if I suffed up, so I can make amends!

Good info, thanks.

Did you correct it for your ambient conditions?

Re VolEff > 100%, Yamagushi says VolEff max = 105 %.

Can you tell us with OBD tool you used?

I'm not an expert in this field, what can we learn from this? How efficient is the MAF? can anything here be improved?

It doesn't tell you anything about the MAFS, but about the efficiency of the rotary engine to pump air into the combustion chamber.
Usually, 4-stroke reciprocating engine have a VolEff between 80 and 90.

Is this an average VE throughout the rev range? I ask because I have seen in excess of 100% VE at a specific engine speed (usually the torque peak).

Don't know, it's a quotation from Professor Heywood. But I guess you could get 100% at a given RPM on some higly tuned and efficient piston engines. But I wouldn't know, as I used tp work on basic Ford engines ...;)

BTW, how is VE measured for rotary engines? I can't find any good resources on this.

I don't see how it would differ from a piston engine. It is a black box positive displacement air pump. The VE is a measure of the theoretical displacement v's the practical displacement.

Also note, my graph is on Mass Air Flow, not volume. The theoretic mass flow is calculated from the displacement volume based on the mass of air at sea level is 1.3 grams/litre.

Cheers,
Hymee.

I didn't make any corrections, but I noted what the temp was, and the BARO according to OBDII.

The CAN interface is manufactured specifically for us.

The software is written by me.

Cheers,
Hymee.

Was this run moving or sitting?

From another thread, it was mentioned that intake temp jumped 120F when the car stopped, and matched ambient when moving with clear flow in front of the vehicle. That big of a delta-T could presumably have some impact on intake mass flow (or does the MAF sensor reading somehow compensate for that?)

It was on the road, full throttle, under load (I used the brakes to load it up like a dyno does).

As far as I know the MAF reading is the actual grams/second. Temperature does not affect the mass air flow. It affect the density and pressure, but a gram of air is always the same number of molecules of air. That is what is important.

Cheers,
Hymee.

Well, it depends on what formula you are using for mass flow rate.

For example, remember the always abused Ideal Gas Law? If not, here it is -

pV=mR[G]T

'p' is the pressure.
'V' is the volumetric flow rate.
'm' is the mass flow rate.
'R[G]' is the ideal gas constant divided by the molar mass of the element.
'T' is the temperature.

Rearraging slightly, you get

m=pV/(R[G]T)

As you can see, the mass flow rate is a function of pressure and temperature.

The other form of the equation for mass flow rate,

m=pAV

where p and V are the same as the above equation, and A is the area, is only dependent on pressure and volume (flame me if I'm wrong).

Here's the real question: does anyone care what I just wrote?

Actually, my real question

was pretty vague. Sorry about that. To find the volumetric efficiency, you must divide the actual displacement by the theoretical displacement. This is one of my favorite efficiencies because it can exceed 100% :D. Same thing with intercooler efficiency. Thermal efficiency is so depressing :(. Carnot efficiency, I can sort of live with :). Anyways, I have the formula for the theoretical displacement somewhere on my computer, so that's one side of the equation. I suppose the only way to calculate the actual displacement is through experiment, or maybe some sophisticated simulation. Man, I'm a nerd :cool:.

I think you abused it all right.

I might need some help here, but the formulae is PV = nRT, is it not?

The mass of x molecules of gas is invariant. Keeping all other variables constant, If you increase the pressure, the volume will decrease. If you increase the volume, the pressure will decrease. If you increase the temperature the pressure will increase etc.

500 pounds of a gas will [b]always[b] contain the same number of molecules. 5 grams of air is always 5 grams of air.

That is why I was talking about the Mass Flow Rate, not the volumetric flow rate. That is why the car uses a Mass air flow sensor, not a volume sensor.

Where is RAP when I need him?

Cheers,
Hymee.

You will find the "actual displacement" in my very first post.

I used the sophisticated sensors and electronics on the car to tell me the Mass Air flow at each RPM point, and it is plotted on the graph.

The theortical displacement does not really require a computer, as we know each rotor displaces 654cc. That makes the theoretical displacement for the engine 1308 cc / revolution, or 1.3 litres. At 1.3 grams / litre for air (at sea level etc.), the theoretical mass flow can be calculated. That is what I did.

Then I plotted theoretical mass flow against actual mass flow and determined the % efficiency (by diving the theoretical mass flow by the actual mass flow).

So you could calculate the actual displacement from the g/s readings the engine was consuming, based on 1.3 g/litre.

So I gave you all the info you wanted...

Cheers,
Hymee.

That's true, depending on how the MAF sensor actually functions (anyone out there know, or know of a post/thread describing it?).

As shellys_man said, the air density varies with temperature. So if you're using a volumetric method, your theoretical mass flow prediction would need to be adjusted (and, depending on how the sensor works, your "real" value may need some adjustment, although that may be done within the ECU since there's also a data channel for intake air temp).

Of course, that's all academic since you were doing these tests moving, because your intake air will be closer to or at ambient temperature if there's good flow in through the grill.

Elevated intake temps would be more due to sitting with the hood closed since the intake ducts are in locations that are conducive to drawing air from inside the bumper, which would get heated by the engine without good flow-through.

All I know is a correctly calibrated MAF sensor is a very sensitive and accurate device. I believe it works on the cooling effect of the air flow on a hot wire.

With the ODBII requirements being enshrined in law, I can't see why I should not have a fairly high degree of confidence in the
reported readings.

Cheers,
Hymee.

Hymee,

Yes you are right. The Ideal Gas Law follows the form

pV=nRT

The form above is as general as it gets. The 'n' here stands for the number of moles of bananas, goats, whatever. There is also a mass flow rate form of the Ideal Gas Law, which was my equation. Remeber that mass flow rate is a derivative with respect to time, or in layman's terms, dm/dt, or an m with a 'dot' over it, which I normally call m[dot]. If I could employ MathType on this forum I would :). Also, volumetric flow rate is dV/dt, or V[dot]. There isn't just one form of the Ideal Gas Law. High school physics is wrong. Thermodynamics is right :). Please forgive me Hymee. I don't want to make you feel as if I am insulting your intelligence. Also, you did note that you found the actual displacement from experimentation. Sorry that I didn't see that :(.

SM6,

No worries, mate.

Cheers,
Hymee.

In a nutshell, it doesn't really matter how you calculated the volumetric efficiency. The point is, you have a result, which you can use to manipulate other variables such as power, torque, heat transfer, thermal efficiency etc. Happy tuning :).

Thanks - that is exactly the point! Happy tuning!

I actually did it as I was thinking about a blower of some sort, and wondered what the actual breathing requirements of the engine are in naturally aspirated form, before considering mass flow rates of various puffers.

So I went and got me some real data, and thought I would share it with you all. :)

Cheers,
Hymee.

You said too much or not enough! Come on spit it out!
What does the soft do?

IKN,

So far the software just makes OBDII PID requests for the operating parameters I am interested in. It decodes the data, and displays the info on a simple GUI on my laptop. It also logs the info to a file. From the file I load the data into Excel, and produce the graph as shown.

The GUI is far from "production quality". But it does serve it purpose - i.e. functional for what I want.

Next step will be to find the correct commands to query/change/reflash the PCM Calibration. :) No mean feat.

Cheers,
Hymee.

Hymee,

Great information here. This data is exactly the kind of information people need to understand this beast.

By the way, I'm sporting a 6mt velocity red 8 too.

To another comment you made. I also agree. Most MAF systems use a hot film anemometer (sp?). What these devices do is they heat the sensor wire to maintain a constant temperature. This results in a change in voltage level to the sensor (note: some are constant current devices and some are constant voltage). As the airflow moves past the wire film. The energy convected away reduces the heat. More airflow causes higher heat loss which results in a need for more input power. Less airflow obviously reduces the power to maintain the sensor temperature. By measuring the power input and knowing the behavior of the hot film sensor. The manufacturer has developed a correlation between the power input and a corresponding air mass flow rate. That's it in a nutshell. However, one of the interesting features of these devices is that they are/can be sensistive to airflow direction. If the flow is prependicular to the hot film sensor, they give good readings. If there is significant distortion or bulk swirl of the flow as it passes over the MAF... them the mass flow reading will be compromised. This is why some "not so well designed" aftermarket inlet systems do not perform well. They have not paid enough attention to the affect they have on the MAF system and air-fuel mixtures are compromised as a result.

Turbine_pwr,

That is an incredibly important point you make about the laminar flow required over the MAF to obtain the correct signal.

I saw so many debates in LS1 land about removing the MAF altogether - but this requires a totally reprogrammed PCM, and requires a MAP sensor. Myself - I am a bit of a believer in having the MAF for it's accuracy, so long as it is not causing a restriction to the flow. If it is, get a bigger MAF - and make sure it is calibrated for the PCM (or vice versa).

I'm glad you like my input of the air flow facts into the FI discuission.

Cheers,
Hymee.

Hymee,

Thanks for the info, although I don't understand what you mean by PID and GUI. Remember, I'm a engine engineer with a mechanical engineering degree! And your profile confirms you're an IT person. But don't worry, I'll do a search on Google before you come back to this forum.

I'm very interested in your approach and project. I'd be happy to help with some info I have on Ford ECUs as it seems to be of the same type as the Mazda. It might be of some help to you in order to better understand which parameter does what.
Note for example that the MAFS readings are most probably not used as a direct input in the fuel or spark table but are used to calculate a 'LOAD' that is used as an input (vs. RPM). Note also that these MAFS measurement are not always used by the ECU to evaluate engine LOAD (e.g. in conditons of backflow although newer generations of MAFS can actually deal with backflow).
By the way, which parameter did you record to get the MAF?

Some other interesting investigations using your CAN and soft could tell us :
- where the engine works in close and open loop fuelling
- when the cat temp protection overfuelling kicks in (you might have to wait for next summer to do so).
- how the electronic throttle body respond to driver's demand, especially at low engine speeds (I have this feeling it's pretty aggressive, giving very good performance feel but perhaps low FE - if it goes WOT fuel enrichment).

I have in numerous posts on this forum already mentionned the problem of potential incompability between aftermarket intake systems and MAFS flow characterisation. The characteristic curve of the MAFS is actually measured with the complete program intent intake system upward of the MAFS !! Any change in the hardware during development leads to a re-cal (or a least a check) of this characterisation!

IKN,

Your points on the MAF are most valid. It may shock you to know that it was previously (probly still is) common practice to tune engines by altering the MAF sensor to trick the ECU into a "more desireable" result.

In fact the Canzoomer controller intercepts the MAF signal and sends a "modified" signal to the computer. Tuning involves finding out how much to trick it at each RPM/Load point.

The PID is a Parameter ID in ODBII speak. There are a whole bunch of them in the SAE docs I purchased. Yes - I have monitored the "Fuel System Status" to watch when it goes in and out of closed/open loop! It is easy to verify on the RX-8 as it has a WIDEBAND O2 sensor that I can also monitor. You can see when it is in closed loop, as the system does very well at maintaining a stochiometric 14.7:1 AFR (Lambda = 1.0). As soon as it goes open loop, you can see the AFR skipping around the place.

The fuel/ignition controller on my car does not intercept and modify the MAF signal. It interceps the signal to the fuel injectors, and tuning involves altering the duty cycle by a % at each RPM/Load (Throttle position) point in a table. Im not exactly sure how it alters the timing, but from studying how it connects to the wiring harness, we believe it intercepts the crank angle sensor input, and adjusts it by X degrees, via a similar table. This modified crank angle sensor signal is then fed on to the ECU. Ingenious in a way. I would rather crack the PCM cal and change it's internal operating parameters.

One drawback is the fuel controller currently only changes one of the three sets of injectors.

And the cat temp can be monitored via ODBII, so I could try and work out then the Cat Protection kicks in.

Anyway - GUI is a Graphical User Interface.

Cheers,
Hymee.

If it is a wide band sensor, it's a type I don't know of because it only has 4 wires (2 for the heater, 2 for the signal). Does anyone has more info about this sensor. All the wide band sensors I've ever used have 6 or 7 wires (NTK UEGO and Bosch LSU). Strange!

There is something Canzoomer should explain to me then. Considering the engine is set to LBT (optimal fuelling for torque) at WOT across the RPM range, what can you gain on a stock engine by modifying the fuelling?
Same thing with the Spark advance, it is usually set to MBT-L (Max Brake Torque - detonation Limited) :
- so the engine already run at MBT (or very close) and you won't gain anything by advancing spark.
- or the engine is detonation limited and by advancing spark at these operating points, you reduce the safety margin built into the system. Note moreover that the knock control has authority and will most probably bring the spark advance back to original level anyway.

Now, if you have modified some hardware (intake and/or exhaust systems) or, better, turbo/supercharged your engine, I can understand the potential of such a fuel/ignition controller.

i can field this.

right from the get go, when we had Speed Racer firing dual 2 ft. flames out of the stock exhaust, 15mi/g fuel consumption, exhaust sooty beyond belief, those not vigilant flooding their cars far too easily, and the highly publicised reduced power rating, we knew something was wrong. what exactly was wrong has been evident, also from the beginning, that the A/F ratios were completely f*cked straight from the factory. the emissions thing, y'know i'm sure.

the thing is, at the original ~250hp rating, you're right that there wouldn't be much to tune in, but since it's now really ~220hp at best, there is a whole lot of room to pick up power simply by leaning it out (back to stoich).
another thing is that all motor wankel engines don't really knock very easily, so you can go rather crazy with the ignition advance (not to mention it's measured in e-shaft rotation degrees, meaning that 3 degrees of advance is really only 1 degree of advance on the rotor) and maybe gain a little (i dunno about Maurice, but Jeff had reported that there wasn't much to get there anyways).

as an engineer, you should know better than to even mention the word "intake", in its usual context, especially this car :P.
the exhaust, i'll give ya, it could definitely use some work. but there is lots to gain in the motor itself, even before you go changing any of that stuff.

1) Problem of fuelling is probably due to tha 'catalyst temperature protection strategy ' (do a search on these word for explanation) and was probably modified (improved) with later coming PCM updates (called reflash on this forum). This strategy only comes in when czlled for (high catalyst temperatures), and probably no more than 3 days a year in Vancouver...
Sooty exhaust : what else would you expect when you burn oil. My wife's diesel also has sooty exhauxt...

2) I still strongly believe (see my posts on this subject) that 'power issue' is just an issue of how ADVERTISED power is determined on different markets (US vs EU vs Japan). I posted the engineering figures as presented by Mazda engineers at the 2004 SAE meeting on this forum (->search) : power is 170kW (231 hp).

3) Stoichiometric fuelling is definitely not optimal for power. And or fuel economy neither. Stoich is just optimal for emission reduction in the catalyst (which must oxydise and reduce simultaneously).

4) Modern ignition systems are very accurate, much more accurate than just 1°CA.

5) If the rotary is detonation free, why does it feature a knock sensor? I guess it's because there is a knock control strategy integrated in the PCM. That has a cost and is therefore integrated on the Renesis for a reason. This reason is that it's detonation limited at certain operating conditions. QED.

6) I don't get the point in you last paragraph. What should I know as an engineer precisely? All I was telling Hymee is that such an auxiliary controller has little interest without significant modifying of the engine and I mentionned intake and exhaust as they seem to be the focus of most mods on this forum.

Measured Mass Air Flow on Automatic
 

Hymee
I decided to see what my RX-8 Auto looks like compared to a standard transmission. As you can see the MAF readings seem to be quite different. At 5000 RPM I was getting 150gm/sec which is above the theoretical line on your chart. At higher RPM's the automatic flows less air and there is a huge drop in airflow at 5600 RPM, I'm not sure why that happens. I was using the CANScan OBD-II tool with the data logger set to 0.100sec per sample.

Sea Level, 80deg. F, 90% humidity.

C.

er, what?? friend, i've been around since well before the first RX-8 frame was welded together. i'm not a member of the SAE, but i know a thing or two. what's with all the down-talk?? you asked, i was just replying in a polite way.

1) duh, that's what i was saying. this is a problem. i know that the exhaust temps are high because of the low amount of metallic mass the exhaust gasses pass by on their way out of the motor, and that they can't just move the cat further back in the exhaust system because it has to cycle through that "quick light-off" feature (the reason for the double walled header) negating the presence of a pre-cat to keep warm up emissions low. so there's the conundrum. the best solution would be to tune the motor back up to where it should be (2000 degree exhaust gasses and all) and get a high-flow catalyst that will either hold up a little better in the heat, or that you choose to afford to replace.

as for the sooty exhaust tips, soot as i'm quite sure you know is hydrocarbonous waste. in this case, where it used to take mere hours of driving to turn the tips from waxed and perfect to sooty black, it was from the high level of hydrocarbons combusting in the exhaust. not even RX-7's with carbs soot up exhaust tips that badly when they're tuned well. deisel will of course soot up exhaust tips, as on start-up (accelerating from a stop) they belch black clouds of sooty black hydrocarbonous waste. and seriously, i know that if you're burning a lot of oil, it burns blue, not black.

2) i strongly believe you are very wrong. it doesn't matter what either of us thinks yet, 'cause it'll take years to find out what's really happened. but the detuning did happen, just ask Maurice (it's the reason the Canzoomer exists).

3) when did i say it was?? "back to stoich", as in toward. it was at 11:1. stoich is 14.7:1, as i'm sure you know. that's a big difference, and a whole long way to tune it. and i do know that for the best power you tune it up on barely the rich side of things, to ensure you consume as much of the oxygen as possible, wasting as little energy on the excess fuel as you can. i also know that these motors can run quite happily on the leaner side of things (Mazda was attempting to get injector spray patterns to concentrate lower levels of fuel in the Centre Deep Depression bathtub thing), which for obvious reasons is good for fuel economy.

4) yeah, that's ok, it's not news to me. i was talking about the relationship of degrees of rotation between the e-shaft and the rotor (which spins at 1/3 the speed), meaning that *30 of ignition advance is only 10* of advance in reality.

5) i didn't say "free of detonation", i said "easily". the knock sensor is there to prevent knock; suppose someone gets a terrible tank of gas, orrrrr the plug wires got screwed with and are getting old, and you've got voltage peaking in all four when they shouldn't be... i dunno. but again, i didn't say they don't knock, nor that they didnt' need a knock sensor and ignition retard safety routine. i did say that you can advance ignition a lot when you're counting degrees on the e-shaft, although it doesn't appear there was much to gain there anyway.

6) the last paragraph was a tongue-in-cheek joke (hence the smilie), as every intake mod is pretty much a bullshit mod. popular doesn't mean good, as is evident with so very many things in our advertising saturated consumer culture :). ricers don't understand how to make cars fast, which is why they're slow.
btw, 20-30 rear wheel horsepower (say, 45-60 flywheel horsepower) for $600 dollars is a whole lot better than the most expensive intake or exhaust system is ever going to get you "without significantly modifying the motor".

That is a good graph CygnusA.

You will find that the dip is when the S-DAIS is changing over the port runners. on the 6PI like mine, there are in fact two dips. And they match the two dips in the power curve (which I didn't plot). The dips on the plot I posted are not noticible, as I only plotted MAF at 500 RPM increments, so I have lost some of the resolution. See any of my posted Chassis Dyno plots, or acellerometer plots and the dips are apparent. It makes it quite apparent that the amount of power being made is related to the amount of air (intake charge) taken by the motor.

Cheers,
Hymee.

I'm not a SAE member (nor your friend as a matter of fact). I don't see any down- talk in my post. Can you? The fact you politely replied does not force me to agree with all you said. You don't need to be around from the very first day on this forum to be aware of the history of the car. Indeed, all the info is archived on this site.
If you look below, we in fact agree on most things.

1) We basically agree on the problem. And there is one otherwise the subsequent PCM updates wouldn't have fixed it. And they apparently did for most. I just doubt the Canzoomer and other auxiliary ECUs can correct the fuelling in a reliable or safe way, especially since the updates came in. I can explain in details if needed (not in this thread) or ask the question straight to Maurice in his vendor thread.
I'll get my first update (Std Power 5MT) next Wednesday. I'll see if the sooty exhaust remains.
And anyway, I prefer to sacrifice a few hp for better durability, especially for costly parts like a catalyst.

2) Compared to the initial figure of 250 hp (marketing cock-up?), I might be wrong indeed. But I'm convinced this engine delivers 231 hp on the engine dyno and that it's advertised at 240 hp in US for the reasons mentionned in my other post.

3) Apparently "back to stoich" confused me.

4) We agree, great.

5) So basically, you cannot 'go crazy' with the ignition, can you?

6) Thanks for the clarification. Sorry but I don't understand that particular smilie. We agree on the intake BS. Especially when you read all the problems some people have had after installing them .

Time to jump in.

The issue with the catalytic converters is really not as big of a deal as Mazda would have you believe. Yes it needs to heat up fast but with modern technology, there is no reason why they couldn't program the ecu to run a different timing/fuel mixture to get a hotter exhaust which would heat up the cat quickly. After the car senses operating temperature the map changes. It would be simple. The old 13B rotaries had hotter exhaust gasses and their cats could be made to last. The last nonturbo rotaries had 3 cats in series. 2 small cats for early lightoff and then a large main one. The small ones were very close to the engine yet these could last to 100,000 miles. The cat would not be an issue if Mazda would tune the damn thing properly. From the maps I've seen, they aren't even close to how I'd do it. Yes, we all agree that the cat lightoff situation is a current issue. It shouldn't be though.

The power issue goes back to the whole improperly tuned thing. The RX-8 doesn't make 247 hp and probably not 238 hp in it's current state of tune. The engine is easily capable of it though as has been varified by Paul Yaw and others. This isn't an engine issue. It is a tuning issue.

Stoich is not optimal for power but it is the best for emissions. Stoich is 14.7:1 on pump gas. Nitromethane is 2.5:1 !!!!! Rotaries make best power near 13:1.

Spark advance is measured in degrees of eccentric shaft rotation not in degrees of rotor rotation. Wakeech's 1/3 less for rotor rotation is correct though.

The knock sensor is obviously there to prevent detonation. Detonation isn't an issue on a naturally aspirated rotary. This assumes of course that it is tuned properly. The way I tune n/a rotaries, I can't get detonation. It is difficult. Why does Mazda have a problem with it? Once again it is lousy tuning. This is the running theme here and the source of all of our problems. I've seen their maps. They suck. They are overly complex and make little to no sense. Tuning should be kept simple. Mazda isn't doing it this way.

Basically there is only one issue that is really the cause of the problems that have been going back and forth here. Tuning.

Yea for Hymee. I hate the term "volumetric efficency". I don't even know what it is.
Do you remember when your professor took a big pyrex bell and hooked a pump through a manometer? You know a u shaped tube with a given amount of mercury in it? When he pumped the air out the pressure would go down. And the opposite.
Did the volume change under the bell???

Of course not, it can't. The bell is the same size so the volume is the same. Now is there more orr less air in there?? yes there is, but this is mass.

So no matter how well or poorly your engine pumps air it alwways pumps the same volume.

Therefore, in order to fuel the engine properly the ECM must know the mass. If that were not the case this would be a lot easier.

I havn't read this whole tread and I;m going to do so right now. I just wanted to put that in since it is one of my pet peeves.

To answer one other question, of course mass flows over 100% is possable even on slightly modified engines. Without knowing for sure I wouldn't be supprised to see the Honda hi po engines dong this stock.
My ski boat engine is fairly high performence modified but not a race engine and it showed 109% on the dyno. And that was carb restricted. I could have gone to a bigger carb and lost some intake vacuume. More properly, increased the intake pressure, But the set up as it was gave better control when pulling up skiers.

Back to the thread. It is very telling that the 8 is pulling down very close to 100% stock. This means Mazda has done it's job.

Ok I'm going back and read this thing and will speak up later.

RAP

I thought we had reached an agreement on this thread. I stopped after Hymee and I agreed on that stuff we were talking about.

yeah, that it's measured in e-shaft degrees means that seeing an insane number like 15* or 24* of advance can be "normal" for a rotary as it's only 5 or 8 degrees (respectively, of course) of ignition advance.. which is what i meant by "advance like crazy".

and thanks for the backup. sheesh.

Bis repetita placent!

What do you technically mean by 'their maps suck'? Can you be more specific (on both fuel and ignition) as you're one of the happy few who saw them?

It's true that the OEM strategies are very complex and would not make sense to an engine tuner whose only focus is on performances. But it does for an OEM engine management system calibrator who has (like engine harware designers) to find the best compromise between the following (sometimes antagonist) aspects :
- durability
- performance
- driveability
- fuel economy
- exhaust emission legislations
- customer requirements
- drive-by noise
- etc.
and this for a global market (= different requirments) that includes Rovianemi (Finland) and Lake Havasu (Arizona).


Hymee, I can't wait for you to post more interesting graphs with other parameters, like lambda, spark advance, mid-cat temp...

I can't find a CAN OBD tool so far in Europe. I keep searching. Which one did you buy?

Sorry to bring the dead back to life, but I found the thread somwhat interesting given the subject. And I've also been bugging some people about this for the past month or so.

I logged data in a similar manner, using Harris R&D CANScan tool with a PDA. I logged RPM & MAF input through out a 3rd Gear WOT run. Having said that, I only plotted Volumetric Efficiency. And I assumed that the Renesis would have similar characteristics to a 2.6 4 stroke engine.

http://smpc.dnyp.com/mazdarx8/charts...y.020205.a.gif

Any comments are welcome!

Nice plot,

At a quick glance, and doing some correlation between the different way we plotted our axis, it seems very similar to what I measured.

Your assumption on the theoretical displacement of the 13B is correct. It displaces 2.6 litres of air every 2 revolutions - the same as a 2.6 litre 4-stroke piston engine.

Cheers,
Hymee.

i know i am jumping into this thread, but i just wanted to put my .02$ on volumetric efficancy. as to moving more air than the theoretical volumetric efficiency, it is quite possible, even without forced induction or ram air. its called harmonics. look at the integra gsr, with long and short intake runners, the rx-8 with all the different runners, lexus and their high output motors, all with variable length intakes.

reason behind the different lenght runners, as the air moves down the intake tract, it resonates, and the resonation is directly related to engine rpm. at certain points in the rpm, the resonation (sound waves) actually benefit the intake charge by pushing a little more air into the motor than it would have otherwise, so there are different length runners that are tuned to different frequencies. thats why the aem v2 intakes make more power than a standard cai.

again, just my 2 cents

i'd like to see someone do this with a revi... for some reason i think it would show to be pretty worthless under 8ooo rpms, but you never know -shrug-

[*]Hello Hymee, I am thinking about to add a centrifugal supercharger to push the near-ambient intake pressure to 1.3 - 1.5Bar. To do that I am about to pair the flow diagram of the chagrer to a natually aspirated RX-8, but did not find any excel sheets about RPM-air mass flow- except what I found here as you mentioned it, but I am quite new here and did not find the attachment or list if there is any. May I ask you to send it to me? Thanks, Janos [/list]

It's an 18-year-old thread and the member was last online 11 years ago. You won't get a reply.

You can start your own thread or if not able to, there is a newbie thread where you can ask for help.