OK bs
Thread Starter
JK Junkie
Joined: Aug 2007
Posts: 2,911
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From: Broken Arrow, OK
Humm... let me run some numbers here, tell me what you guys think...
2289 RPM x (57.0 kPa / 50.0 F') ---- Here I am assuming "Absolute temp" means the Intake Air Tempurate"
Engine Mass Airflow = 2289 RPM x 1.14 kPa/F' = 2609.46 RPMx(kPa/F') --- WTF is this unit
Fuel Mass = 2609.46 / 14.7 = 177.514 --- I gave up on units bob
So here I am with a fuel mass of 177.514, but I am not sure what a fuel mass is or how to go from here to MPG... still reading
Okay, so I'm closer...
MPG = 710.7 * VSS / MAF
VSS = Jeep speed in kilometers per hour.
MAF = Mass Air Flow in grams/sec * 100
The first part of the quoted equation seems to be trying to estimate MAF for vehicles without a MAF sensor (like our Jeeps)...
At the time I took these measurements my OBD data puts me driving at 45/MPH... or 72.42048 Km/H.
so MPG = 710.7 * 72.42048 / MAF
or MPG = 51,469.2351 / MAF
But what is my MAF
Thread Starter
JK Junkie
Joined: Aug 2007
Posts: 2,911
Likes: 0
From: Broken Arrow, OK
Okay, still digesting this, but I found this tidbit...
As for other ways of doing this, especially if you don't have a MAF sensor, by knowing the displacement of the engine, and after a simple "calibration" using fuel tank "fill-up" data to find the only unknown, namely the "volumetric efficiency" (VE) of the engine, MAF can be calculated from RPM, MAP and IAT. With VE, one can use the following formulas to calculate a synthetic "mass air-flow" (MAF) in grams per second, all without a MAF sensor, using the "Ideal Gas Law", as follows:
IMAP = RPM * MAP / IAT
MAF = (IMAP/120)*(VE/100)*(ED)*(MM)/(R)
where manifold absolute pressure (MAP) is in kPa, intake air temp (IAT) is in degrees Kelvin, R is 8.314 J/°K/mole and the average molecular mass of air (MM) is 28.97 g/mole. Note that, in the above formula, the volumetric efficiency of the (4-cycle!) engine is measured in percent and the engine displacement (ED) is in liters.
The VE of my 1999 7.4L Chevy Suburban is about 65%. Smaller, higher performance engines can have VE's of 85% or higher.
IMAP = RPM * MAP / IAT
MAF = (IMAP/120)*(VE/100)*(ED)*(MM)/(R)
where manifold absolute pressure (MAP) is in kPa, intake air temp (IAT) is in degrees Kelvin, R is 8.314 J/°K/mole and the average molecular mass of air (MM) is 28.97 g/mole. Note that, in the above formula, the volumetric efficiency of the (4-cycle!) engine is measured in percent and the engine displacement (ED) is in liters.
The VE of my 1999 7.4L Chevy Suburban is about 65%. Smaller, higher performance engines can have VE's of 85% or higher.
JK Jedi
Joined: Feb 2009
Posts: 4,012
Likes: 0
From: Lawton, OK
Looking good 
How's the ride?
Such a brave brave man 
. I was lost after the first = . Here's how I figure mileage - I fill it, she drinks it - we move ahead in time, and miles. It all works out
So long as you don't do a gender change, you're safe. But, is there such a thing as a Soccer Pop?
The visual on that was funny!!!
He should be able to feel a disturbance in the force . That, or his Droid (spelt Wookie).
Yep, I sent him a text message
Gotta make sure someone's there
How's the ride?. I was lost after the first = . Here's how I figure mileage - I fill it, she drinks it - we move ahead in time, and miles. It all works out So long as you don't do a gender change, you're safe
. But, is there such a thing as a Soccer Pop? The visual on that was funny!!!
plus his JEDI powers enable him to communicate without electronics.... That, or his Droid (spelt Wookie).Gotta make sure someone's there
JK Jedi
Joined: Apr 2008
Posts: 4,273
Likes: 0
From: Broken Arrow, Oklahoma
Originally Posted by u-joint
Okay, so I'm closer...
MPG = 710.7 * VSS / MAF
VSS = Jeep speed in kilometers per hour.
MAF = Mass Air Flow in grams/sec * 100
The first part of the quoted equation seems to be trying to estimate MAF for vehicles without a MAF sensor (like our Jeeps)...
At the time I took these measurements my OBD data puts me driving at 45/MPH... or 72.42048 Km/H.
so MPG = 710.7 * 72.42048 / MAF
or MPG = 51,469.2351 / MAF
But what is my MAF
JK Jedi
Joined: Feb 2009
Posts: 4,012
Likes: 0
From: Lawton, OK
