IAT question

[joecar]

Odd Boy,

It didn't make sense until I realized your calculator failed you...

So if we assume that the ECT is 80 C and IAT is 30 C, the correction temperature will be 273.15+IAT+((ECT-IAT)*factor )==> 273.15+30+((80-30)*.6) = 347.15 K.

Now will assume that the IAT is -40 C, the new value will be 375.15 K.

I get:
273.15+30+((80-30)*.6) = 333.15K
273.15-40+((80+40)*.6) = 305.15K

1. When IAT = 30 C, corrected temp = 347.15 K :

g/cyl = VE*MAP/charge temperature ==> g/cyl = 80*35/347.15 = 8.06

2. When IAT = -40 C, corrected temp = 375.15 K :

g/cyl = VE*MAP/charge temperature ==> g/cyl = 80*35/375.15 = 7.46

80*35/333.15 = 8.40 g/cyl
80*35/305.15 = 9.17 g/cyl

(I know you are just using VE = 80 for example sake... the VE would be closer to something like 2-3 g*K/kPa.)

Regards
Joe

[odd boy]

It is sweet when u get confused and then clear. Correct me if I'm wrong, the elaboration I made is right (apart form the calculation part)

[joecar]

Your elaboration seems to be correct (you correctly used the concepts of temperature weighting and VE "actualization").

Just remember that the VE table is not a percentage, but it is a normalized value having units g*K/kPa, and by applying charge pressure and charge temperature (under the conditions in which the charge entered the cylinder) you obtain the actual VE in g.

[joecar]

The result of your elaboration using correct calculation would be that at -40C the VE is almost 10% greater (richer) than at +30C.

[odd boy]

Thanks, and think about posting my+ur write up with the required corrections and result

[Sid447]

As I understand it,

Assuming the same atmospheric pressure and elevation; an IAT/OAT of 30c gives a higher Density Altitude than -40c does.
Therefore if the D.A. is higher which means the air is thinner or has less oxygen, it doesn't require as much fuel (to maintain a decent AFR) and the power drops as a consequence of this.
(Though there is some payback with less drag and thus less power required for a given speed depending on temp lapse rate).

If the IAT is not signalling the PCM to decrease fuel in higher temps and increasing it in lower temps then maybe GM have got it wrong and need to compare notes with with an aero engine manufacturer like Pratt & Whitney.

http://www.obd2crazy.com/techdiat.html

[odd boy]

See what we came with, it is in line with ur understanding

The result of your elaboration using correct calculation would be that at -40C the VE is almost 10% greater (richer) than at +30C.

Use these two graphs as a future reference



Should u have any question u can call me on +966504699641.

[joecar]

The second graph shows it... cold air is denser than hot air... we don't even have to mention DA (to keep it simple).

I don't follow why you say GM got it wrong...?

[Sid447]

The second graph shows it... cold air is denser than hot air... we don't even have to mention DA (to keep it simple).
I don't follow why you say GM got it wrong...?

Understanding DA is the whole foundation of air fuel mixture and performance!

Anyway if post #10 is a fine example then I'll say no more.

[joecar]

I didn't see in that link anything that says differently that what was discussed... I am considering what you said and I didn't want to miss the point... ... I want to understand everyone's insight.