Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

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Drwaffles
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Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby Drwaffles » Tue Sep 18, 2018 8:59 pm

Just a quick tip that might catch a few people out, thought I'd share.
If you're planning to set your own Air temp compensations instead of the Auto function, and want to use the ECT/IAT bias (You should)...

Make sure that your temp axis in the Fuel - Air temp correction table is set to "Calculated air temp - CAT"
If it's set to IAT it pretty much negates the ECT/IAT bias tables purpose. It's pretty basic stuff, but thought I'd mention it as I see quite a lot of people have turned the auto function off.

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Mobne_s13
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Re: Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby Mobne_s13 » Fri Sep 21, 2018 5:28 am

I noticed that my calculated air temp was way higher than actual value.

I’m using the auto VE air temp.

You have any clue why?

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Drwaffles
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Re: Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby Drwaffles » Sat Sep 22, 2018 6:17 pm

Check under sensor properties, "Coolant Temp Bias"
CAT is used to estimate how much heat the intake air picks up through your entire intake tract.
The higher the % in that table, the closer it'll read to engine coolant temperature.
Set to 100% you're telling the ECU that air temperature is the same as coolant temperature.
Set to 0% you're saying the air is making it through the intake and past the valves picking up zero heat along the way.

This table need to be tuned correctly (It's a bitch to do) to ensure stable mixtures under various conditions.

Mobne_s13
Posts: 277
Joined: Sun May 25, 2008 8:56 pm

Re: Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby Mobne_s13 » Sun Sep 23, 2018 9:56 pm

Do the air really heat up that much in the intake?

If I have 20 degrees air temp going in my plenum.
What is then realistic the temp is when it enters the cylinder?

The m3 has really good intakeports.

Anyhow the engine is tuned and I never changed that because i had no idea about it. Maybe best to leave it alone now?

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Drwaffles
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Re: Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby Drwaffles » Mon Sep 24, 2018 11:45 pm

Yup, can heat up quite significantly especially at lower loads.


That's the thing.. it's dependant on manifold design, material (Plastic or metal), valve and cylinder head temperature, how long you've been running the motor at that particular airflow (more air coming over hot parts will slowly remove some heat from those parts)
Depends on vehicle speed, how much airflow into the engine bay, ambient temperature, how much air the engine is currently consuming, what fuel type and how much latent heat is that Injection absorbing..
How much internal EGR is heating up the remaining fresh air.
so many factors, near impossible to accurately account for all.
Short answer, I really can't tell you lol.

Intake port design has minimal effect on temp transfer, it's mostly the air volume/speed and head temperature.

If it's tuned, leave it alone unless you feel like redoing your entire VE table. Plus CAT is a bitch to tune, you have to hold steady state (or datalog the same cell) and varying intake temperature for each load site.

LotusEsprit1000
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Re: Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby LotusEsprit1000 » Sat Sep 29, 2018 11:10 am

New guy question. If I am running a MAT sensor do I need this? I have not gotten the software downloaded yet. I am going to tonight after work.

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Drwaffles
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Re: Quick Tip: Something to be aware of when NOT using Auto VE air temp compensation.

Postby Drwaffles » Wed Oct 17, 2018 11:35 pm

Need, not really.. Should run, absolutely :)


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