Intake Air Temp Sensor Relocation??

[Sammo 2544]

After I installed an intake on my 330ci, I did a bit of IAT tracking via an OBD2 app out of interest.

I realised how badly heatsoak appears to affect the IAT readings when in traffic, or even just after the car has been at temp for a while.

I feel like acceleration is more laboured when this happens but could be placebo - do high intake temps pull timing? I would often see readings of 55-60c at an ambient temp of 15c... so much for a 'cold air intake' doing anything.

The IAT in the PFL E46 M54 is buried in the intake apparently making it very susceptible to heatsoak - was in the MAF in later E46's.

Any point in trying to relocate somewhere cooler or am I just wasting time on a  non issue on a slow car?

[BreakMyWindow 1874]

I think IAT and KTMP have an influence on spark ignition timing. 

If the engine feels sluggish after crawling traffic or on hot summer days it's probably a good thing (so long as it feels better with cooler air, and there are no other engine faults) The dme is protecting the engine from likely damage as a result of pinging.

You really want a dyno when playing around with this kind of thing imo.

[Sammo 2544]

@BreakMyWindow that is a good point, probably more useful things to spend energy on - generally if I want to hustle I'll be on a nice open road Sunday blast anyway... 

[M3AN 4016]

Relocating it will only hurt, it will send the wrong data to the DME. Intake air temp is measured for air density (volume) not actual temperature and the car fuels accordingly.

The lower temp the better (more dense air ergo more volume) so trying to bring that down is a good goal. Wrapping your intake in heat shielding can make a difference but you need to consider whether it's actually worth the effort. As you've noticed it only really helps when you're going slow or not moving at all.

However, if your IAT never gets close to ambient (e.g. at speed) then your intake is inefficient.

[Sammo 2544]

14 minutes ago, M3AN said:

Relocating it will only hurt, it will send the wrong data to the DME. Intake air temp is measured for air density (volume) not actual temperature and the car fuels accordingly.

The lower temp the better (more dense air ergo more volume) so trying to bring that down is a good goal. Wrapping your intake in heat shielding can make a difference but you need to consider whether it's actually worth the effort. As you've noticed it only really helps when you're going slow or not moving at all.

However, if your IAT never gets close to ambient (e.g. at speed) then your intake is inefficient.

Yeah, it comes down very quickly once moving (you can see big dips whenever a decent amount of throttle is applied)  - will just leave the sensor alone.

Heat shielded short ram with insulation and factory ducting.

 

[zero 1162]

This is a very interesting topic.

A good test might be to swap the stock intake back in and take the same readings and see how much different it is.

 

A long shot idea, but would a cooler running fuel like gull force 10 have an impact on intake temps?

You could also experiment with heat guards on the headers etc

[m325i 709]

1 hour ago, M3AN said:

As you've noticed it only really helps when you're going slow or not moving at all.

So the perfect mod for an Auckland daily

[BreakMyWindow 1874]

1 hour ago, zero said:

This is a very interesting topic.

A good test might be to swap the stock intake back in and take the same readings and see how much different it is.

 

A long shot idea, but would a cooler running fuel like gull force 10 have an impact on intake temps?

You could also experiment with heat guards on the headers etc

I'd imagine Gull force 10 would have an impact on combustion temperatures rather than the fresh air being drawn in. IAT's or "sucked air temperature" is the temperature of the air being drawn in to the intake manifold before it gets used to combust.

If IAT's are cooler then the dme adjusts the fueling and timing accordingly which results in more efficiency, more power and torque. It is the MAF which calculates how much air volume is being drawn in to the cylinders.

A few years back I ran an experiment on a dyno by putting one of the M5's maf's (that is used also to measure IAT's as it has an integrated sensor) in the fridge for 10 mins in between dyno runs. The result was about 10rwkw's more peak with IAT slightly over ambient vs about 30deg C over ambient on the first run.

[M3AN 4016]

Be careful about what you read on the internet.

In cars with a MAF sensor, like yours, the IAT sensor is only a failsafe (and a great diagnostic tool), if you unplug it you will notice no difference at all as long as your MAF is working properly.

 

[BreakMyWindow 1874]

I think you’ll find there’s a difference with the iat disconnected, certainly on a dyno measuring afr’s. This is absolutely the case with the ms52 dme programming and suspect also true for ms43 dme’s too.

 

[M3AN 4016]

M52, M54, M56, straight from BMW:

https://www.newtis.info/tisv2/a/en/e36-320i-cou/wiring-functional-info/power-train/engine-controlms42/air-supply/intake-air-temperature/Y1duGiq

You guys are just making stuff up.

[BreakMyWindow 1874]

44 minutes ago, M3AN said:

M52, M54, M56, straight from BMW:

https://www.newtis.info/tisv2/a/en/e36-320i-cou/wiring-functional-info/power-train/engine-controlms42/air-supply/intake-air-temperature/Y1duGiq

You guys are just making stuff up.

 

Making stuff up? 

I’m sharing the results from my experimenting on a dyno with s62 iat’s and made the assumption that iat’s can influence fueling on the m54 as well, but perhaps not the case with the ms43. (M54 engines).

[BreakMyWindow 1874]

I found this on the MS43. I think really the only way is to do some data logging or dyno testing to see what effect the iat has on fuelling, timing, engine power.

 

[M3AN 4016]

4 hours ago, 3pedals said:

From the TIS website " 

 

TIS is BMW's knowledgebase, ISTA and DIS contain exactly the same info.

Edit: I didn't see all the other replies but I'm going to believe BMW. smh ?

Edited September 23, 2020 by M3AN

[M3AN 4016]

1 hour ago, 3pedals said:

Suggest you read the other replies and refrain from rash comments like 'no qualifications' and 'questionable agendas' neither of which apply in this instance, there is  just the evolutionary process of dialogue  shaking out some assumptions in this  thread and that's reasonable.

You're right about that, sorry (now edited).

With respect to your comments, sometimes I just find them overwhelming. I'm comfortable with my acceptance of BMW's technical documentation in this case.

Edited September 23, 2020 by M3AN

[BreakMyWindow 1874]

Well to anyone that thought TL;DR for this, Dave found comfort in a paragraph he found on the internet. 

He also accepts himself.

[Sammo 2544]

2 hours ago, 3pedals said:

For the O.P regarding heat soak. 

 Probably worth expanding on my original assumption with a bit of an explanation around heat soak and intake temp.

Heat soak - As an engineer my schooled view of  "heat soak" is the thermal transfer through the mechanical structure i.e from the engine block into the manifold  and associated components - historically heat soak has been countered by using a thermally non conductive gasket or flange between the head and the manifold. In later years with  fibre reinforced nylon manifolds , this is not required. 

Radient Heat absorption - often lumped in with heat soak but technically  different - this is where a component absorbs heat from its surroundings - e.g the alloy plenum non an M3 will absorb engine bay heat and then radiate it into the cooler inside of the plenum - raising the internal temp. 

The third mechanism is Ambient heat in a confined space,   heat under the bonnet  builds up when the vehicle is stationary and the ventilation is poor. - This is what I have responded to in my initial reply to your post. 

Relocating the IAT will have an effect in the first two instances,  but not for the third - the problem here is you are ingesting hot air and the measurement is real and essential that you preserve it as real.

 The solution is to ingest cold air. 

 

 

Thanks mate - and thanks all for the robust debate - a little initial research had indicated conflicting data, as evidenced in this thread.

I am thinking for my purposes, its probably not worth messing with moving the sensor as I'm hardly drag racing stoplight to stoplight in traffic and the airflow is great on a spirited drive when I actually want the power.

As to ingestion of hot air, my intake does use the factory kidney ducting and is heat-shielded (including from the expansion tank and with proper thermal insulation backing) and reasonably sealed off so I would hope its not too bad - certainly about as good as an open cone filter would get.

Anyway, I made this change for sound alone, while trying not to lose performance, I may well go back to stock once I install my Supersprint backbox if it sounds good enough to ditch the intake.

I love the induction roar, but there is an annoying whistle on part throttle that comes with it...

[Sammo 2544]

@3pedals Do you get any 'whistle' with the E36 intake?

Seems to be an issue with any open type filter with the E46 - great induction tone, but comes with an annoying accompaniment... 

[M3AN 4016]

You guys should let BMW know you think you've found a mistake in their technical documents, they'd probably appreciate that.

They might send you a free pen.

[BreakMyWindow 1874]

Something tells me you’ve got a box full of them.

[M3AN 4016]

5 minutes ago, BreakMyWindow said:

Something tells me you’ve got a box full of them.

No, the last time I wrote to BMW was in in the early 90's and I got a invite to their Mt Wellington headquarters. That was cool of them to do. They send pens to people they don't have time for.

And I don't disagree with their technical documents but we've already established that. It was a suggestion for people like you who claim to know better than BMW themselves. ?

 

Edited September 24, 2020 by M3AN

[kwhelan 241]

21 minutes ago, M3AN said:

No, the last time I wrote to BMW was in in the early 90's and I got a invite to their Mt Wellington headquarters. That was cool of them to do. They send pens to people they don't have time for.

And I don't disagree with their technical documents but we've already established that. It was a suggestion for people like you who claim to know better than BMW themselves. ?

 

what part of their disclaimer do you not understand

 

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Edited September 24, 2020 by kwhelan

[polley 916]

I'm starting to think M3AN is an elaborate troll.

[BreakMyWindow 1874]

51 minutes ago, M3AN said:

No, the last time I wrote to BMW was in in the early 90's and I got a invite to their Mt Wellington headquarters. That was cool of them to do. They send pens to people they don't have time for.

And I don't disagree with their technical documents but we've already established that. It was a suggestion for people like you who claim to know better than BMW themselves. ?

 

What colour Bimmersport pen would you prefer?

[Michael. 2313]

You'd probably find the stock intake performs perfectly for your intended use. It's not always an accident how the parts end up after the BMW engineers developed them. 

It's an interesting topic to consider. 

Any time the intake is drawing in hot air from under the bonnet the sensor will read higher temps, so the ECU will change the timing and fueling to suit, resulting in less power. Terrible for off the line performance, or waiting for a run down a drag strip. 

I did some real world tests in my Soarer with 3 sensors, one on the front bumper for ambient, in front of the air filter, and one behind the airbox outside of it. Here is a table of my findings based on different time spend doing different things, at different speeds. 

As you can see any time the car comes to stop the hot air in the engine bay quickly accumulates 

I had a modified airbox that was drawing in hotter air than it should, so I returned it to stock. I did take new readings and they were much closer to ambient, although I didn't get around to making a table up for that. 

To be fair, I would suggest returning to stock as well. 

Edited September 24, 2020 by Michael.