ok im gonna go out on a limb here and think about the MAF, these are mostly assumptions i am making so DO NOT LISTEN TO ME. im just asking the experts if this "assumption" is right and could help with tuning.

the next statement is not yelling but i just want people to understand i am no expert lol THIS MAY BE TOTALLY WRONG, I MIGHT SOUND LIKE I AM IN DRUG BUT I HAD A THOUGHT TODAY ABOUT IT AT WORK AND FIGURED I WOULD ASK. this may have been brought up before but i dont know, so i am bringing it up myself.

ok so we start off, the MAF sensor is just that, a mass airflow sensor. i measures the amount of air comming in. what is the measurement on MAF is it lb/min? or something like that?

ok from what i have learned in thermodynamics class is that the mass flow rate is equal to the density of air times the area times the velocity. right now the only variable in there that is not known is the velocity of the air. the area is constant, the density of air is also a known constant depending on altitude. this is most likely the factor that throws off each maf sensor, it all depends on where the calibration was done.

so if the density of air used could be determined for the scaling and the density of air in our own area was known, could we not scale the maf to more accuratly measure the air comming in?

ok well take out the area and the velocity for a second. the velocity times the area will give you the volume flow rate, the volume of air that would have to be flown could be determined based on cubic inches per a certain amount of time. there for we would know the desired volume flow rate for each rpm. from this, we could obtain an equation and find out what the desired table for our cars would be.

now here is the problem. these mass air meters are not at the calibration we need, so we must make the tables work so we get desired results. could we not then just log MAF vs. rpm until we get the entire table built? i could do the calculations for the volume flow rate and then everyone would have to multiply this by their specific density of air for their area and that should yeild the desired flow rate. then just comes the long process of getting the whole tables right. i have no idea what the tables look like so i dont knwo if and how this can be done. but someone let me know if this sounds like its on the right track.

i will talk this over with my thermodynamics professor and see what he has to say about it. it sounds like it makes sence to me. i am only a jr. in mechanical engineering and am not through thermo 2 yet, so this may not be right, but sounds good to me. so why not post? i know there are lots of engineers out there so i figured this may have been brought up, but nothing hurts in asking.

if i wasted your time im sorry lol but your welcome if you were just trying to kill time on here lol

 

what is the standard bore and stroke on an ls1?

 

the maf sensor is 75 mm and the TB is 78 correct? oversized MAF is prob the reason of error in tuning cars. the maf sensor should be the biggest restriction, however only a little smaller than others such as the TB. therefore the maf calcualtions can be accurate.

got the bore and stroke

 

from my calculations i have, the diameter of the mass air meter doesnt matter. the motor demands at 800 rpm 1.20165072677 lbm/min as long as i didnt screw up in the calculation. right now my car reads about 1.00 so my calibration should be off. so tuning for maf shouldnt be for fuel trims it should be to get the right numbers. all tuning should be done elsewhere. make sense or should i drop out of engineering lol

just gotta ask about when the restrictions of the maf and tb come into play if they do, for the velocity of the air. pretty much have to see if the air happens to reach a "terminal velocity" where only so much air can flow.

i would also assume that the fuel that is injected would have to be accounted for but that is easy to do once i can figure out how long the injector stays on for. anyone know how man ms that the injectors stay on for?

 

OK a few things that I would like to point out as i am no expert myself, but we can at least discuss!

I think the velocity is accounted for by the response the MAF reads as frequency. I think the travel or whatever those little MAF wires do, is your velocity variable. (Been too long for physics so not sure where we're going with the calculations). We then know that velocity is covered by frequency, density is determined by lovely mother nature, and area is supposed to stay constant (the plane of a cross-section of the MAF housing is our area) but when people port their MAFs, or go with larger units, that is the only variable that becomes "unknown" to the PCM. The motor however knows this variable since it obviously uses whatever airflow it receives to satisfy it Volumetric Efficiency.

This can't be as easy as it sounds since air density is temperature related amongst other factors probably as well. Like, isn't colder air more dense? And yes altitude will also cause density to vary. The MAF does not measure density though, it measures frequency which is related to air velocity I think... the density is a predefined user input on the MAF table itself isn't it (ie. lbs, grams, etc)

I've though about this, but something to consider: let's say we are 2000 rpms right? this could mean that I could be going 10 mph in 1st gear, or 80 mph in 6th gear. I don't know what the spread is, but I'm positive the MAF reads more air going 80mph, as opposed to 10 mph. I think this is why we can't necessarily look at the MAF airmass in terms of rpms.

Don't be afraid to question or formulate since it seems you have some sort of deductive reasoning process! lol I don't know if I answered in the way you were hoping for, but maybe this will jog some of the juices!

 

I thought the TB was reduced from 78mm to 75mm. I think the acutal Tb blade is 75mm but they start at 78mm to help airflow transitions, etc.

 

this is exactly why i saw DO NOT SCALE!!! lol Even through calculation we will not be exact, but much more exact than just across the board scaling!

I dunno what terminal velocity the MAF or TB might have, but I'm sure we're not hitting it since people that go with FI setups definitely push more air through the same sensor we have.

Injector Pulse Widths

 

you are right, the density of air IS dependant on not only temperature but also the atmospheric pressure.

m (mass air flow) = p (density) * a (area) * v (velocity)

V (volume flow rate) = a (area) * v (velocity)

the V equation can be determined without a or v. you can calculate this from the air the motor has to have, the volume of air that has to go through the MAF at that certain rpm. leaving speed out i would think that at 2000 rpm, the engine would need the same amount of air. maybe this is the problem with the maf. like i said im no expert just going on the knowledge that i have. i almost made and A in thermo 1 so i guess i know enough to bring it up.

i am almost positive that the maf does measure the velcity of the air but it converts it. i would think this equation is in the computer and it just takes that velocity for a known area and calcualtes for the density i has as a constant also. if the area changes, the velocity changes. this is why u have to calibrate it for those new velocities. get where im going with this? if the maf and tb are the same diameter that is good. the maf has the wires and what not that reduce the area, which is known.

did i lose u on this or u still follow?

 

ok so the injector is rated at a certain flow rate, i was thinking into it too much that should be enough to know right there.

 

i would think we could find a density that wouldnt throw off the readings so much, maybe a happy median that would result in small variance of reading. say if you live in an area that only sees a low of 30 on average but i a high of 90 then i would think tungin for 60 would be best right?

 

My head hurts from reading this post. I think the answer to your question is yes?

 

hahahaha

 

I'm assuming that it would matter by how much change their is in air density between 30 degrees. Also, wouldn't humidity factor into the equation? I'm not sure with naturally aspirated engines but I did a lot of work with my old '98 grand prix gtp and humidity gave me heck trying to tune and working with the maf.

 

im my thermodynamics book it says all the densities are given at certain atmospheric pressue and temperature. those are the only 2 parameters it mentions. maybe with compressing the air, the more humidity the more it will effect it. i will find that out too.

 

density is an intensive propert and is constant mass, according to the book.

proportional to pressure and inversely proportional to temperature

 

The density of a substance (mainly gases) depends on temperature and pressure. Gases are usually compared at a standard temperature and standard pressure. These are the freezing point (0 °C) and normal air pressure at sea level (760 torr), respectively.

The density of dry air at sea level is 1.2929 kg/m3 or about 1/800th the density of water. But as altitude increases, the density drops dramatically. This is because the density of air is proportional to the pressure and inversely proportional to temperature. And the higher you go into the atmosphere, the lower the pressure gets. Pressure is approximately halved for each additional increase of 56 km in altitude. To determine the density of dry air at a given altitude we could use the relation D = D0(T0/T)(P/P0) where D0 is the known density at absolute temperature T0 and pressure P0 and D, the density at absolute temperature T and pressure P.

Just as there is a density of dry air, there is also the density of moist air, or air that contains moisture (humidity). To obtain this density you can use the relation D x (273.15/T) x [(B - 0.3783e)/760]. Where...

D is the density of dry air at sea level,
T is the absolute temperature,
B is the barometric pressure in mm, and
e is the vapor pressure of the moisture in the air in mm.

Rachel Chu -- 2000

 

http://hyperphysics.phy-astr.gsu.edu...watvap.html#c1

here is a link to calculate vapor pressure. i think with all these parameters we could come up with a better calculation for conditions in our area of the country. with these factor we will never have a perfect tune unless u change the tune for the weather each day. this will get it pretty damn close i think. i would think closer than anyone has come on it, with that much calculation involved. lol

 

i wish i could hit the dyno on a basic tune and then dial it in for that specific day. i wonder what kinda difference will be seen

 

physics aside, the motor sees the variant weather/airflow conditions, whereas the MAF is calibrated at a more specific particular condition. I say calibrate the MAF to your motor in what you would call "medium-type" weather and let it be an intermediate bias for all weather conditions. No matter what the motor never operate completely inline with the MAF, so just find a place that works as an anchor!

We can jibber jabber about all the physics we want, but we have all the tools to do MAF recalibration in front of us. However the MAF derives it's airmass formula, the motor does the exact same calculation in the Volumetric Efficiency (Dynamic Airmass). In a perfect world the MAF would not be variant from that dynamic airflow. That's the "physics theory" if you will... But as we can apply that concept, we also know that this is not a steady-state perfect condition world so we know the motor's calculations will vary as it sees fit for operation. The MAF calibration on the other hand is just a non-adaptive, user input function. The goal is to get the MAF as close as possible to encompass this variety of driving conditions as it will never be perfect!

 

yeah thats what i was thinking about. how does that process sound? similar to how you did yours or what? i emailed my professors to see what they said.