False alarm!

Can anyone else second this motion before I start tinkering with my settings?

Thought I'd share what the values do so that you can see for youself how the code impacts fueling based on tempature and the various % in correction scaling.

The fueling is scaled by the % calculated in the last two columns (one is for 100% MAT scaling, the other is values used at 50% MAT scaling).

I'll admit I was quick to think a bug exists, but I still do feel the calculations are probably not ideal... note how the band of no correction (shown around 68-70F where it is at 100% correction) is only a small area whereby changing from 100% to 50% MAT scaling doesn't impact when a change is seen based on the rounding and resolution used in the maths in the code.

Interesting and I'll continue this in the MSExtra forum to see if I can get James or Ken to respond and reply.

Oh, and the calculations are the same in MS3 and MS2.

And the fueling is just multiplied by that %... so if the fueling says 4.40ms and the AirCorrection is 105% then the new fueling is 4.62ms.

G

Cool, the numbers look to be correct for the 100% values with respect to ideal gas law...i see no issues so far.

Where are you sourcing this from - ie how do you know that 80F should have only 2% less fuel ???

The fact that at 116F it is pulling 8% of fuel sounds great unless you are in boost on the track on a hot day in Miami and your AFR that should be ~12 and you are seeing a very dangerous 13.5.

exzactly.

I haven't looked at the code or anything... but I'm guessing it does something along these lines.

Based on the that table let's saying the code is using 21C/70F as it's 100%...ok cool. To calculate percent difference from that assumed "standard value".... I'm going to use Rankine cuz i'm in 'merica....

New temp 120F

(delta T) / (Abs temp original) = ((70 - 120) / (70+460))*100+100 = 90.56, rounded up to 91

Now I'll admit I've messed around with 68-72 as the 'starting value', and none of them match up exactly with the table you posted up....every now and then one value will be mismatched by 1, might be due to how MS if it's rounding the numbers intermediately along the way or something, I'm not sure.

As far as the validity of this.. i may be off in my thinking, but I was using the P=rho*R*T equation.... P and R are constant for our purposes, which leaves rho (density) and T(absolute) to be inversely proportional... ie temp increases by 2 percent, 2 percent less air mass for a given pressure...needs 2 percent less fuel. BUT we're probably getting into the weeds here into theoretical stuff, that probably does not apply exactly for us. If any of my thinking or logic is off, let me know what you think, definitely open to discussion and learning.

this is the formula:


n = PV/RT
=> M = n x MM = PV/RT x MM
= (VE * MAP * CYL_DISP) / (R * (IAT-32) * 5/9 + 273)) x MMair


P = VE * MAP (i.e. the pressure in the cylinder in kPa),
V = CYL_DISP = the displacement of one cylinder (in liters),
R = 8.3143510 J/mol K,
and T = (IAT-32)* 5/9 + 273 to convert IAT from °Fahrenheit to Kelvin.





Then to calculate fueling:


Req_Fuel is calculated from the equation:

REQ_FUEL*10 = 36,000,000 * CID * AIRDEN(100kPA, 70°F)/(NCYL*AFR*INJFLOW ) * 1/DIVIDE_PULSE

Where:

36,000,000 is the number of tenths of a millisecond in an hour, used to get the pounds per 1/10 milllisecond from the pounds/hours rating of the injectors.
REQ_FUEL = Computed injector open time in tenths of millisecond.
CID = Cubic Inch Displacement.
AIRDEN = Air density (pounds per cubic inch) at MAP pressure of 100 Kpa, Air Temperature of 70 Degrees F, and Barometric Pressure of 30.00 In HG
NCYL = Number of Cylinders
INJFLOW = Injector Flow Rate in pounds per hour.
DIVIDE_PULSE = injection divide number for number of injections per engine cycle.



The AIRDEN function (used above) is defined by:

AIRDEN(MAP, temp) = 0.0391568* (MAP*10-31.0)/((temp+459.7) * 1728)

Or, in metric units (kg/m3, °C, kPa):

AIRDEN(MAP, temp) = 1.2929 * 273.13/(T+273.13) * MAP/101.325

Would it be hard/possible to change Gair resolution to 0.1%? I don't think that's gonna solve anything like guys have talked about in here, but seems like a good idea overall for more accuracy. I've really liked the other recent changes in finer resolution... EGO, etc.

I dunno I dont really have a problem with the resolution of the table. I'm able to completely negate the density correction... It was as simple as putting the MS on a stim, turning the AIT input pot, and watching how the Gair reacted. I tuned it out completely within 0.5% (in some spots Gair stays at 100.5%--not going to make or break me).

When I always brought up the issue, it's been assumed that my AIT is reporting false temps, therefore that's scewing up the code. and to use the Mat corrections table in the fashion I do is only solving the flawed data from my sensor.

but i have proven that my sensor reports back readings that are very close to readings under the hood as seen by a second identical AIT sensor.

So while the gas density law is law. what the fueling code doesn't take into effect is how the temperature of say the block of even the fuel relate to the air density.

As far as driving, if I need different fueling requirements base on temp, my EGO takes care of it and in boost my AFRs are very consistent and flat regardless of the ambient temp...so I dunno what to say.

If it ain't broke (for you), don't fix it :)

yeha pretty much. if I was road racing it, I'd wanna test the effects more...but just doing boosted pulls on the hwy or something, I have no issues. I've barely touched the tune on this thing in over a year and the thing I've tuned were random odds and ends, like new idle code and the new accel-pump and stuff.

MS3 is 0.1% increments.

MS1/2 is 1.0% increments.

So is there consensus that on my MS1 I should set the CLT related air density correction to taper off at 7200 and tune it from there?

unsure, can you confirm the leaness is actually the gammae going below 100%?

i dont ever remember having this issue on MSI I always had it decay starting at 2500 and finishing around 5000 IIRC.

I will put the gammae gauge on the dash and try to simulate the track environment and find out.

So you see major swings in air temps, but claim it makes zero difference to AFR and a simple way to turn it off completely would suit you.

There is an easy ini change that can be made to allow 1% scaling which would Pretty much turn it off.

G

Pretty much. I mean I guess i need to start looking at my EGO logs...doing what I did pretty much did "turn it off"