Where's your IAT? (CSL guys)

[Slideways]

The US and EU-spec IAT sensors have distinct resistance-temperature curves and scaling. I'm curious if these placement differences + scaling differences impact performance and warrant a closer look.

Based on this thread, the US-spec IAT in the lower duct seems to deliver a smoother driving experience for those who switch, possibly due to more accurate ambient temperature readings.

As Karter noted, the tune + the associated scaling is likely the dominant factor here. I'm curious if anyone has experimented with both setups and can speak to these scaling changes and how they impact driveabilty and overall performance.

CSL has one location for the IAT and that is in the airbox.

The IAT Evolve uses and the IAT most tuners recommended putting in the lower duct is from an E34/E36. Based on the information Karter posted, this is not the preferred IAT setup.

[AWE46M3]

The US and EU-spec IAT sensors have distinct resistance-temperature curves and scaling. I'm curious if these placement differences + scaling differences impact performance and warrant a closer look.

Based on this thread, the US-spec IAT in the lower duct seems to deliver a smoother driving experience for those who switch, possibly due to more accurate ambient temperature readings.

As Karter noted, the tune + the associated scaling is likely the dominant factor here. I'm curious if anyone has experimented with both setups and can speak to these scaling changes and how they impact driveabilty and overall performance.

[amiao]

Wow Karter16 thank you so much for helpful information. There’s so much chatter about the different locations and this helps clear things up. I’m going to be running a full CSL DME with Bryon’s mullet tune. Thank you for your contribution

[karter16]

I'll throw this into this discussion.

When designing the CSL BMW's engineers wrote code specifically to address and account for heat soak as a result of the stock IAT location. This code is not present for the standard M3, it was written specifically for the CSL as a result of the differing IAT location.

The original post is here and I've replicated the content below.

TL;DR: Yes heat soak needs to be considered, but BMW's engineers were also aware of this and there is code in the CSL program specifically to deal with and account for this. If you move the IAT from the stock location you are giving the DME a false representation compared to what it is expecting.



Okay here's one for those who are concerned about heat-soak and the location of the IAT sensor.

The CSL software has additional code in the function that calculates TAN (intake air temperature):



Lines 16 to 26 are not found in the standard euro software. These lines are calculating a version of TAN specifically for the purpose of being used in the CSL's calculation of air mass, which in turn is used in the calculation of final RF as we've seen previously.

k_tan_m_cfg is set to 1 in the 0401 partial:



which means that tan_m is set from what I've tentatively named tan_m_adj.

How is tan_m_adj calculated? Like this:





The key thing to understand about this function is that it is iterative. It runs every 100ms and the previous result is used to calculate the next.

So what are the key behaviors?

To simplify it down a lot, the function basically:

1: Starts with IAT (measured intake temp)
2: Compares it with TMOT (motor temp) and blends it to some degree based on:
3: ML - load

At high load tan_m_adj is pretty just TAN, at low load conditions where the engine is idling the tan_m_adj function is distrustful of what the IAT is telling it and calculates tan_m_adj more and more heavily based on tmot the longer the conditions continue.

Why is this model needed? It is specifically to deal with heat-soak at idle and at stop conditions. The model prevents situations where the DME trusts the IAT in heat-soak scenarios. This would be bad as it would result in lean running conditions. The tan_m_adj model gives the DME a more realistic understanding of the actual intake temperature to ensure that lean conditions don't occur.

It's a bit hard to graph, but this kind of shows the response of the model at various levels of load:



This isn't completely representative of how it works in reality as it is based on a fixed TAN reading, when in reality TAN will rise quickly due to heat soak, but what this graph does show is that at higher load levels the model heavily favors actual TAN (higher airflow = more accurate reading) at lower load levels it skews towards TMOT over time.

I can't come up with a good way to graph or visually represent an actual scenario of a car coming to stop at the lights and the behavior of TAN and tan_m_adj, so you have to just work it through in your mind.

Essentially this a fairly complex model which is tuned to handle IAT heat soak scenarios and give the air mass calculations a more accurate IAT value in those scenarios. The model is iterative and adjusts the tan_m_adj value further towards TMOT the longer the heat soak conditions continue.

What's the lesson? Don't mess with your IAT sensor - the software is specifically calibrated to deal with heat soak conditions.

[amiao]

Hey all, I’m gearing up to do install a Karbonious Manifold with their snorkel as well. I was planning on using the CSL IAT sensor, since I have the snorkel will I be okay with leaving it in the stock location? Or will I also eventually suffer from heat soak over time? From this thread it seems like the stock location might not be the best location, however it seems like most people who are having issues aren’t running it with a snorkel. Does using the snorkel eliminate this issue?

[siamkazi]

I was using the IAT that came with the turner box (this was back in 2021 at Autoclub Speedway here in SoCal in the early summer) when we started noticing idle hunting, lights on dash, and the motor running lean. If I recall, it was reading temps super high, was chatting with Hassan and the suggestion was that the IAT was heat soaking. Came back, used the current IAT and relocated to the duct, had Hassan make some changes, and it's been smooth ever since (including sessions at Buttonwillow etc). Mind you, this is my own story so I'm just sharing my experience.

[beyondm3]

Exactly. BMW Did loads of developement with the IAT sensor in the airbox. Heatsoak or not, allowances in the original CSL tune must have been made to account for the IAT's position.

Fair points.

I'm curious what other symptoms people experience from the heat soaked sensor other than reporting of higher temps. I seem to have only read about higher temp readings and not so much lower performance and the like.

[Slideways]

Exactly. BMW Did loads of developement with the IAT sensor in the airbox. Heatsoak or not, allowances in the original CSL tune must have been made to account for the IAT's position.

Yeah, CSL IAT sensor in its factory location works well, so no real reason to change it. If you search realOEM, the older E34 style sensor was used on cars from 1985-2000. The CSL style sensor was used on cars and bikes post 2000.

[ac427]

INPA or Testo

Also, I'm not sure why the tuner is suggesting putting the Beru (E34) sensor down in the lower brake duct intake tract. The air going into the intake manifold won't be nearly as cold as that area. The engine will be reading a colder air temp and my guess is throwing more fuel into the engine.

On the other BMW engines using this Beru sensor, it is mounted either in the intake manifold or after the air filter. I think that the CSL snorkel or better yet the unfiltered section might be a better location to mount this air temp sensor.

Exactly. BMW Did loads of development with the IAT sensor in the airbox. Heatsoak or not, allowances in the original CSL tune must have been made to account for the IAT's position.

[Slideways]

How are you guys checking the IAT values? INPA or a "hidden" OBC function?

Sorry for the noob level question

INPA or Testo

Also, I'm not sure why the tuner is suggesting putting the Beru (E34) sensor down in the lower brake duct intake tract. The air going into the intake manifold won't be nearly as cold as that area. The engine will be reading a colder air temp and my guess is throwing more fuel into the engine.

On the other BMW engines using this Beru sensor, it is mounted either in the intake manifold or after the air filter. I think that the CSL snorkel or better yet the unfiltered section might be a better location to mount this air temp sensor.

[elbert]

How are you guys checking the IAT values? INPA or a "hidden" OBC function?

Sorry for the noob level question

[digger]

to me the CSL sensor looks better as it would probably have a faster response time than the threaded brass one

[liam821]

https://www.bimmerworld.com/Intake-F...621725323.html

this the guy?

FCPEuro sells this one which is what I used: https://www.fcpeuro.com/products/bmw...or-13621739510 for $17. It's the same scale as the e46m3 CSL IAT sensor.

[marksae]

https://www.bimmerworld.com/Intake-F...621725323.html

this the guy?

Yep, that's the one.

[beyondm3]

https://www.bimmerworld.com/Intake-Fuel/Intake-Sensors/Air-Temperature-Sensor-E36-E34-E31-13621725323.html

this the guy?