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Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

(OP)
Application: Forced induction Gas Engine

Do my own tuning, want to write my own calculator so I can plug in VE and HP (all other variables being at STP, etc)
And come up with Mass Air requirement, which I can convert ot KG/Hr

For sizing or calibrating MAF measurment range.

So
I know how to get Theoretical CFM = (CID * RPM)/ 3464

Hp = (Torque * RPM) / 5252
700 = (x * 7000)/5252
Torque = (700 * 5252)/7000
Torque = 525.2 (if that matters)

I'm just having trouble finding an equation to plug in PEAK HP, VE, and get Airflow of some type (all else Standard)

Thanks for any insight,

Don

RE: Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

So
I know how to get Theoretical CFM = (CID * RPM)/ 3464

Hp = (Torque * RPM) / 5252
700 = (x * 7000)/5252
Torque = (700 * 5252)/7000
Torque = 525.2 (if that matters)
-----------------------------------------------------

in Computer Languages, its faster to use multiplication rather than division , and won't get a "divide by zero" error

the 3464 should be 3456 (.000289352)

Theoretical CFM = CID * RPM * .000289352

or

Theoretical CFM = CID * RPM * .000289352 * Ve%

Hp = Torque * RPM * .000190404
700 = x * 7000 * .000190404


Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

RE: Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

one more algorithm that might help you ?

very simple but accurate algorithm to calculate

Fuel Consumed in Lbs/Hour = Engine_RPM * CID * .0001

where ;
CID = cubic inches
.0001 = constant from 3 other constant values

example=> NHRA Pro Stock Cars w/ 500 cid

Fuel_Consumed = 9000 * 500 * .0001
Fuel_Consumed = 450 Lbs/Hour

estimated BSFC = .36

estimated HP @ 9000 rpm = 450 / .36 = 1250 HP

the 1250 HP would be the "UnCorrected, Raw HP" before a Weather and Friction Correction Factor were applied

so the 1250 HP could windup as much as 1320 Peak HP or so depending upon Weather/Friction Correction Factor used in Dyno Tests and Dyno Test acceleration rate Rpm/Sec

agrees very well with these calculations ;
http://www.maxracesoftware.com/Quick_HP1.gif


if you wanted to estimate SCFM
then
SCFM = Fuel_Consumed * A_F_Ratio * .217898

from those equations
you could calculate the theoretical Ve %
or the actual Trapped Ve%

BSFC's will range from .34 to .50 normally
anything higher than .50 is considered very inefficient


Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3

RE: Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

(OP)
Thanks for the quick reply, and great info.

I'll have to labor a few calculations, and after I tune a few of these I'll know more about the BSFC's and efficiencies.

On a Roots blown 4.6 with 650rwhp, these variables are going to throw off the equestions/results, but atleast I can get an approximate window before I have some hard results for a specific combo.

Thanks again,

Don

RE: Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

It is common for supercharged and turbocharged applications to have BSFC ranging from .60 - .65 as they frequently run excessive rich mixtures so fuel dumping can be used to control detonation.

The BSFC for the Subaru WRX (turbocharged) is about .59 based on the info I have seen.

Larry

RE: Deriving Mass Air Flow, or Volume Air Flow, based on VE and HP

This is just a thought but if you a trying to determine load tables isnt it just: 4l engine at 50%load = 2l etc?

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