AFR drift vs IAT

[schpenxel]

Exactly like CC-Rider said has to be custom OS which are free these days. All you need is to convert Kelvin to Celsius. Like I said though, outside temps make a difference so it's not just what the IAT sees but the density of the air outside which I guess is also why GM went with MAF as it's less susceptible to air density changes I could be wrong but it's what I'm seeing consistently which I wish I did not.

Still doesn't show up on mine for whatever reason

[cc-rider]

Odd. Here's how it shows up on mine. E38 2010 Camaro SS ECU transitioned to a HPT 2 bar OS.

charge temp mult.jpg

[schpenxel]

I'm on an E40 so that's probably why

[realcanuk]

I'm on an E40 so that's probably why

Must he the E40.. I have that table also.

[cc-rider]

Well here's a log file showing this IAT drift phenomenon. Started my car up and let it idle for about 30 minutes (in SD mode with MAF failed). You can see it started off rich when it was cold IAT (80F) and ended up lean at higher IAT (120F).

Start up 3 in VE - IAT drift.hpl

And I think I fouled out a plug (or two) doing this. f#%@!!!!! You have no idea what a pain it is to change plugs with this Kenne Bell blower on. Went to take it for a ride after this test and it was not running on all cylinders and had a pretty bad engine shake. Need to diagnose.

[cc-rider]

Little off topic update related to my fouled plug comment in the post above. Or I should say, at least what I thought was a fouled plug. Turns out I blew out a plug wire. I installed some headers and one of the plugs was touching the header ever so slightly. Thought I'd give it a go and see if it held up with an insulated heat sock over it. No luck. Wore through and started shorting out in just 25 miles.

In some ways...that's good because at least I didn't foul a plug.

[cc-rider]

Mourat,

Bringing this back around to your comment to ensure I understand it. Are you saying that the injector mult table doesn't transfer across to VE at all? I would think that the injector mult table would affect both VE and MAF? An IAT reading doesn't care weather we are running in MAF or VE...right?

I can fully understand that the VE mult table would only apply to VE. I guess I'm confused why the injector mult table wouldn't apply to both MAF and VE.

Not questioning your info here...just wondering if you've got some more info or a may know the logic on why it doesn't work for VE. Thanks!

[Gelf VXR]

Its not just air that changes density with temperature, fuel does too, IAT transfers heat to (or away from) the injector, as does ECT to a lesser effect, as the engine warms up so does the engine bay and fuel line, increasing fuel temp above outside and fuel tank ambient temperature, when sat in traffic IAT rise significantly increasing the temperature of the fuel injector. As things warm up the fuel in the injector becomes less dense, OL AFR drifts leaner. The rate of change of fuel density vs temperature is a good fit to the IAT modifier in the LS9. Something else to consider.

[cc-rider]

Its not just air that changes density with temperature, fuel does too, IAT transfers heat to the injector, as does ECT to a lesser effect, as the engine warms up so does the engine bay and fuel line, increasing fuel temp above outside and fuel tank ambient temperature, when sat in traffic IAT rise significantly increasing the temperature of the fuel injector. As things warm up the fuel in the injector becomes less dense, OL AFR drifts leaner. The rate of change of fuel density vs temperature is a good fit to the IAT modifier in the LS9. Something else to consider.

Interesting data. Thanks for sharing. My data log showed me that I've got about a 1.4% AFR drift for every 10 degrees temp change. Very similar to that ZR1 data you showed there.

[LSxpwrdZ]

That must be the computer's way of adjusting for outside air density changes. That's why when you artificially cool down the intake air charge (via meth or intercoolers) it will make it run a bit rich. You aren't making any more oxygen in reality, but you just told the computer you did. Perhaps you can lower the temp adjustments in your tune to be less additive and it won't go as rich.

A lot of people make the mistake of thinking because their intercooler cools the air charge down that there is now more oxygen to make more power. That is simply a widespread misconception out there. More oxygen density can only come from the atmosphere, and oxygen cannot be "manufactured" in the intake system by cooling. But that's not to downplay the wonderful effects of good intercooling. A car can't make more power with a cooler charge no doubt. But it doesn't come from more oxygen. It comes from timing and even AFR.

Nitrous and meth, on the other hand, are a whole different ballgame. Can add combinations of cooling, oxygen, and octane to the charge.

I have to disagree. I have logs that show reduction in fuel consumption as charge temps rise yet lambda stays the same. Depending on where you place the meth injection nozzles determines how the blower utilizes the air it's pulling in. Spraying methanol pre-blower really helps keep air density up and will create more power.

Think about it this way, how much oxygen is in 1 sq.in. of air when it's 60*F compared to 160*F?

[sssnake]

Very good discussion. So what do you do when you have an intercooled engine with a single IAT sensor post IC? The IATs now don't track with heat load under the hood that Gelf mentioned. I have this issue to the extreme (7% swing). The only correction I have found is keeping heat out of the engine bay. It would be nice to be able to adjust something in the tune but I haven't found anything that I can use. Thankfully things trim back out within a few minutes of driving but I have had to eliminate LTFT because of the issue. I would end up hitting an LTFT cell that was adjusted while heat soaked causing a large rich condition. It was definitely noticeable

[cc-rider]

I have to disagree. I have logs that show reduction in fuel consumption as charge temps rise yet lambda stays the same. Depending on where you place the meth injection nozzles determines how the blower utilizes the air it's pulling in. Spraying methanol pre-blower really helps keep air density up and will create more power.

Think about it this way, how much oxygen is in 1 sq.in. of air when it's 60*F compared to 160*F?

I'm not sure exactly what part you are disagreeing with? What I was trying to say is that more oxygen density cannot be created inside your air intake system by traditional intercooling methods (i.e. water to air intercooler bricks....or a2a intercoolers). The amount of oxygen coming into your intake from the atmosphere is all that you will get.

However, if you add oxygen inside the intake system like spraying NO2 then you can indeed increase the oxygen density inside your intake system.

I was simply trying to make the point that traditional intercooling methods (not spraying anything) do not add oxygen density. They just cool the charge. A lot of people think that because their intercooler is more effective at reducing boost temps that they have more oxygen than the comparable system that does not cool as well. Not true. You just have a cooler charge and the same amount of oxygen.

[sssnake]

He is disagreeing with your statement that: "more oxygen density cannot be created inside your air intake system by traditional intercooling methods" because that is exactly what an intercooler does. The cooler the air the more air density. The more air density the more oxygen density. Filling one 1l chamber with 30 degree air and another 1l chamber with 100 degrees air results in more oxygen molecules in the first chamber (30 degrees). This is because the air and therefore the oxygen is denser.

BTW - this is why your AFR wanders with IAT. Well at least one of the reasons.

[cc-rider]

He is disagreeing with your statement that: "more oxygen density cannot be created inside your air intake system by traditional intercooling methods" because that is exactly what an intercooler does. The cooler the air the more air density. The more air density the more oxygen density. Filling one 1l chamber with 30 degree air and another 1l chamber with 100 degrees air results in more oxygen molecules in the first chamber (30 degrees). This is because the air and therefore the oxygen is denser.

BTW - this is why your AFR wanders with IAT. Well at least one of the reasons.

Wrong. And that is the exact message I was trying to get across. Cooling your intake charge down with a traditional intercooler heat exchanger system does not create more oxygen density. It just cools the charge. Oxygen cannot be manufactured inside the intake tract. Higher oxygen density in colder temps are a phenomenon of the earth and the atmosphere. When temps cool down outside your intake tract in the atmosphere, then oxygen density is indeed higher.

That's not to downplay the benefits of cooling the intake charge down. Which are plenty. But you will not be creating higher oxygen density by doing it inside your engine.

If we still have disagreement...I'll try to find some references later when I have time.

[cc-rider]

He is disagreeing with your statement that: "more oxygen density cannot be created inside your air intake system by traditional intercooling methods" because that is exactly what an intercooler does. The cooler the air the more air density. The more air density the more oxygen density. Filling one 1l chamber with 30 degree air and another 1l chamber with 100 degrees air results in more oxygen molecules in the first chamber (30 degrees). This is because the air and therefore the oxygen is denser.

BTW - this is why your AFR wanders with IAT. Well at least one of the reasons.

To use your example above...about filling bottles with air at different temps air....let me use this to explain better.

If you take the 2 bottles and fill them up with outside incoming air that's at 30 degrees and 100 degrees...then yes, the 30 degree air bottle will have more oxygen.

However....take 2 bottles and fill them up with the exact same incoming air (let's call it 100 degree air)....then cap the bottles and stick one in a chamber that cools one bottle down to 30 degrees and the other in a chamber that heats the air up to 270 degrees....and then measure the oxygen content in both. They will have the EXCAT same oxygen content.

Follow me? It's the incoming air that determines the oxygen content....not what you do with the temp of that air once it's entered the system.

[cc-rider]

Found the reference I was looking for. Read post #25 in this thread here: http://www.camaro5.com/forums/showth...=158601&page=2

This is by Jim Bell...the owner of Kenne Bell superchargers. He probably can explain much more eloquently what I was trying to get across.

[schpenxel]

Your point is valid.. whatever amount of air goes into the supercharger is all you're getting at the intake.. cooling it won't spontaneously make more of it.

[cc-rider]

Ok...back on topic here. I've got some pretty neat data to report here. My initial data log with no correction factors put into the tune showed an AFR drift of about 1.25% per 10 degree of IAT increase. So I took that 1.25% drift number and entered it into both the VE mult table (as Mourat suggested) and the IFR mult table (split the difference between both tables).

The result...my IAT drift was gone. Went from an IAT of 65 to 120 degrees with the AFR not drifting.

Here are the 2 datalogs...before/after:


Start up 3 in VE - IAT drift.hpl

Start up 4 in VE - IAT drift corrected .0125 in both ve and ifr.hpl

[schpenxel]

Neat!

[cc-rider]

Does anyone know if there is a mult table somewhere to adjust fuel vs ECT? I can now see that there is also some drift that occurs with ECT as well.

I know about the open loop tables. But those adjust the commanded AFR. I'm looking for something that would fudge VE or IFR to correct for ECT just like we have been discussing here for IAT.