pistonsuk

Hey I am working on an engine CFM calculator that will tell the exact CFM of your engine based on injector duties and AFR. This will be useful when selecting a new turbo.

I am curious what our engines flow. So I am asking for a datalog because I dont have access to my car right now.

This will work best if you datalog a long pull in 3rd or 4th from 2k-redline. (Of course on a closed course, or dyno

If you have a datalog with this displayed:

Inj Duty
RPM
Boost
AFR (or a voltage from a wb and the chart used to convert it)

email it to: rotor_rage@yahoo.com

You must also tell me what injector sizes you are running, where your staging bar is and your static fuel pressure.

Please include a mods list: porting, exh turbo size A/R etc...

I will post the excel spreadsheet when I am done.

Justin

crispeed

Do you mine explaining to me how the two are related?

NeoTuri

iTrader: (2)

I don't think logging boost is a reliable way of measuring air flow. For example, you can have 20psi boost but nearly zero CFM if the air does not have any velocity. In such an example, there is nearly as much pressure coming back from the port intake as the compressor side.

MAF sensors do this not boost.

pistonsuk

This is my reasoning:

Airflow=Fuelflow * AFR
=(InjDuty)*(# of Inj)*(size of Inj)*AFR

make sense?

Justin

pistonsuk

I only wanted boost logged so I could say:

Example: 13BT, 15psi, 60-1 turbo, streetport = 400lbs/min @ 4000 and 650lbs/min @ 7000

^ these are not real. Just an example.

all i need to calculate lbs/min of air is AFR and lbs/min of fuel.

Justin

pistonsuk

NeoTuri

sweet avatar....

NeoTuri

iTrader: (2)

Thanks,

To get back on topic, I will be datalogging AFR, load/boost, injector duty, etc as soon as I get the FD back together in the next week or two.

pistonsuk

Great. Would you be willing to share this? I am looking into a GT4088, I would like to know what efficencies ranges I will be operating near.

Justin

NeoTuri

iTrader: (2)

When that happens I'll post what I find here.

cardzrule

In hondas you gotta know teh fuel pressure too. are mazdas different?

Also how you gonna know teh weight of air and fuel?

pistonsuk

No. Like I mentioned in the original post I must know both the fuel pressure that the injectors were flowrated at (usually 43.5psi) and the base pressure (fuel pressure @ 0psig manifold pressure) of the system you are running. I also made the assumption that people are running 1:1 regulators. I dont know why anyone w/ a standalone would run a rising rate regulator.

Injectors are volume-flowrated (cc/min), this can be converted to mass-flowrate (lbs/min) by simply multipling by the density of fuel. There are calculators online for this. At this point you then have a mass-flowrate (lbs/min) of fuel which can be multiplied by the AFR (air to fuel mass ratio) to find the mass-flowrate of the air.

Justin

cardzrule

So you saying that fuel weighs teh same no matter what temp? Dont racers cool their fuel 2 get more in teh tank? How com fuel dont get hotter when pressurized like air does from a turbo? Also dont teh fuel get hot going into teh hot engine bay? Also you saying that 20 psi of air weighs teh same as 0 psi air and that 50 deg air weighs teh same as 200 deg air? Whats teh point of cai and fmic and turbos if teh air weighs teh same? Sorry im too dum to understand teh math dood but it dont make sense to me.

Also AFR aint all that accurate is it? I mean even teh widebands dont read rite when they get hot or when air is flowing into teh exhaust from air pump or exhaust leaks.

pistonsuk

No. But I did make this assumption. I searched the internet and could not find how the density of gasoline varies with temperature. If you can let me know, I can include that in the calculations; although I doubt it will make much difference.

It does, but not much at all. Liquids are assumed to be incompressible when analyzed under these conditions. This amount of heat added is negligable.

Sure. But how much does this change the density of the fuel? I would suggest not much at all. Again if you can find how density varies with temp, I could correct for this.

Nope. The pressure and temperature is taken into account when calculating the mass of the volume of air.


From FJO's website: Accuracy better than 0.1 AFR over the range 10.5:1 to 15.5:1

Justin

cardzrule

Ge i still dont understand how you gonna figger out teh cfm if you dont know teh weight of teh air. Guess i need more schooling.

o you didnt say teh datalog had to have a fjo wideband. Most peeps have teh stock narrowband 02 sensor. Also i think that fjo accuracy is in a lab and not on a real car. Those engineer doods dont know real world stuff too well.

Also i got a question. If teh wideband sensor only works 750-850 C temp
http://www.pectel.org.uk/assets/NTKWideBand.pdf
wich is same as 1382-1562 F
http://www.onlineconversion.com/temperature.htm
and teh rotery engine exhaust is 1650-1700 F
http://www.rhinoracing.com/yaw/carb_tuning.htm
then how can teh sensor be accurate if its past its temp range? Teh way i figger if teh company sez teh senor works good 1382-1562 F then that mean it dont work good more or less than that. So if teh rx7 is more temp than that then there aint no way teh sensor gonna be 0.1 AFR accurate on a rx7 like fjo sez. Make sense?

cardzrule

Maybbe i can understand better if you show one ez math problem?

Inj Duty 80
RPM 5000
Boost 10
AFR 11

You must also tell me what injector sizes you are running
550

where your staging bar
NONE

your static fuel pressure.
43.5

Please include a mods list: porting, exh turbo size A/R etc...
street port - stock s4 tII turbo

OK so what is teh cfm for that?

pistonsuk

Welcome to school....

Density is a ratio of mass (kg) over volume (m^3). Fore example styrafoam has a low density (not alot of mass per unit volume) on the other hand, steel has a much higher density.

Volume is not a ratio of anything. Following the above example: we both know it is possible to have say 1kg of styrafoam or steel. Now the density of these materials would tell us how much space that mass would fill.

Density of almost anything (that I know of) changes with temperature and pressure. Gases are the best representations of this. As I mentioned before when analyzing solids and liquids we assume density is not a function of temperature and pressure.

Therefore if given a pressure, temperature and composition (material, i.e. air) the density of that material is known. Then using the above definition of density if the volume of the material is known the mass can be calulated.

True, and understandably they are expensive. Yes I was reffering to a wideband, narrowband o2's would not be nearly sensitive enough.

I'm not sure what variables are present "on a real car" vs. a lab enviroment. I would still think that the wideband reading can be considered "accurate". At least for the purposes of these calculations.

I hope this is not always the case, I am 12 credits from becoming one.

The FJO supports both NTK and bosch types. I wonder, does the bosch also have an operating range below that of a rotaries exhaust temp? What sensor comes with the unit?

Now, I dont know exactly why they post 750-850C as operating temps. But I do know from experience that it is very common for manufacturers to claim a limited range to their senor simply because it is only over that limited range that the sensor is linear within the specified limits given. For example FJO claims their unit is good to 0.1AFR, this is of course over the specified operating range (750-850C), however the unit may be good to 0.2AFR from say 500-1100C.

Great site, I use this all the time.

This is reffering to a narrowband sensor. It is true these are not accurate far from stoic.

Justin

pistonsuk

Send me your email.

Justin

4CN Air

iTrader: (7)

Yes you do, with the most important class being English! j/k

cardzrule

TY but I aint sending ne1 my email address coz I got too much spam already.

Mr Stevens my science teacher sez you cant calculate cfm with teh info ur asking for neway. Maybbe you should have a disclaimer or something on ur spreadsheet coz peeps gonna be pissed if they spend like 2000$ on a turbo that aint sized rite coz ur math was wrong.

Y you gotta spend ur time flaming me stead of posting something useful?

4CN Air

iTrader: (7)

just having fun bud. consider it a free bump (and a laugh)

pistonsuk

Spam? I am going to email my Excel based spreadsheet to you so you can calulate the CFM of the engine you posted earlier.

I would like Mr. Stevens to look at my spreadsheet too. It would great to hear any educated constructive criticism he has on it.

If either of you are interested pm me an email.

Justin

torean

pistonsuk....glad to see some engineers are putting time into the rotary....

i volenteer to check his math if needed....

hmm....fuel doesnt change density all that much because the fuel's saturation temperature....unless it is in the liquid-vapor state we can assume the density to be constant...to calculate the mass of air u can just consider air as a ideal gas and apply the ideal gas equation....PV=mRT....i would suggest that the data also include intake temp...(not sure if this was suggested)

the WB02 needs to be placed further downstream of the exhaust...they also suggest this on the website so that the engine heat does not ruin the sensor.....18-24inches away from the turbo if i remember correctly.....this lets the exhaust cool down a bit to be measured

torean

btw...by my spelling and grammer u can tell im destined to be an engineer...but damn.....trying to read some of these posts is nearly impossible........its like learning something from a teacher from calcutta

NeoTuri

iTrader: (2)

I'm street tuning today... will post my findings soon

pistonsuk

Any of you that would like a copy of this calulator just PM me your email.

Justin