Tuner gurus: Air temp sensor location?

[Paul Workman]

I have heard/read about and seen a few air temp sensors relocated closer to the filter.

Question:

If one is adjusting the tune by dyno results, is there any andvantage to moving the sensor? I think not, as it is handled in the tune. And I don't see how being a foot closer to the air filter at WOT is going to make any difference. I mean, what is the air temperature delta at two points a foot or so apart, measuring the same air column moving at huricane speeds???

P.

[1990 quasar blue]

I have heard/read about and seen a few air temp sensors relocated closer to the filter.

Question:

If one is adjusting the tune by dyno results, is there any andvantage to moving the sensor? I think not, as it is handled in the tune. And I don't see how being a foot closer to the air filter at WOT is going to make any difference. I mean, what is the air temperature delta at two points a foot or so apart, measuring the same air column moving at huricane speeds???

P.

Great question. I was wondering the same thing. I had it relocated but removed it when I installed my HAT chip since that's supposed to address the situation. I just saw it last night and thought hmmmmm I wonder.

[mike100]

I plugged my original unit back into the harness (the one in the air horn) and it was (TECH1 scanner) reading a LOT warmer than the true ambient- which my relocated IAT reads.

The manifold gets heat saturated and I'm not sure why the IAT doesn't measure reasonable air temps more than it reads the hot manifold aluminum. seems like some newer car designs have IAT's in plastic or rubber intake duct sections.

[GOLDCYLON]

I plugged my original unit back into the harness (the one in the air horn) and it was (TECH1 scanner) reading a LOT warmer than the true ambient- which my relocated IAT reads.

The manifold gets heat saturated and I'm not sure why the IAT doesn't measure reasonable air temps more than it reads the hot manifold aluminum. seems like some newer car designs have IAT's in plastic or rubber intake duct sections.


I think there is a lot of reasoning behind this conclusion. M Haibeck sold a lot of these relocator kits back in the day as well. Unless you have a before or after dyno its anybodies guess.

[bdw18_123]

The manifold gets heat saturated...

That's what I'm thinking too.

It isn't that the air 2 feet away is so much different, I think it is more to do with the metal in the air-horn getting heated up from the plenum/engine getting hot which then transfers to the body of the sensor and then to the actual sensor element that reads the temp of the air passing over it.

So, relocating the IAT sensor more forward away from the heat of the engine results in the sensor getting a more accurate reading of the actual temp of the air going into the engine.

Makes sense to me, but I'm no physicist or engineer.

[XfireZ51]

Moving the Manifold Air Temp sensor to the filter actually re-purposes it as an
Intake Air Temp sensor. Without modifying the calibration, the lower air temps being reported causes the ECM to richen the AFR. There are different values that should be used when the MAT is moved. I'll post a pic of the table that should be adjusted. Trying to find out what the new values should be.

[gbmidyear66]

Moving the Manifold Air Temp sensor to the filter actually re-purposes it as an
Intake Air Temp sensor. Without modifying the calibration, the lower air temps being reported causes the ECM to richen the AFR. There are different values that should be used when the MAT is moved. I'll post a pic of the table that should be adjusted. Trying to find out what the new values should be.

Interesting - this would seem to mean that the AFR conditions should also be changed when one blocks the coolant flow though the TB/Plenum (like I just did). I notice the Plenum/TB is much cooler now - as is the adjacent airhorn and IAT.

[Paul Workman]

Moving the Manifold Air Temp sensor to the filter actually re-purposes it as an Intake Air Temp sensor. Without modifying the calibration, the lower air temps being reported causes the ECM to richen the AFR. There are different values that should be used when the MAT is moved. I'll post a pic of the table that should be adjusted. Trying to find out what the new values should be.

Thanks for verifying that, Dom.

Interesting - this would seem to mean that the AFR conditions should also be changed when one blocks the coolant flow though the TB/Plenum (like I just did). I notice the Plenum/TB is much cooler now - as is the adjacent airhorn and IAT.

Hey, gbmidyear66, you bring up a good point.

Mike100 said he saw a significant difference in MAT readings when comparing the mount locations; at the air horn and in the tube leading from the air filter. And, therefore, apparently the temp of the material the sensor is mounted on compromises the MAT reading accuracy. :(

That being the case, then logically it would make a lot of sense to isolate the sensor from heat being conducted from the engine. Bypassing the TB coolant has a huge affect on the temp of the TB and the plenum - perhaps negating the need to move the MAT to the filter area...perhaps. However the benefit to the DIS module running cooler is reason enough alone to bypass the TB; stabilizing the MAT temp is just a nice bonus!

In any case, I suppose moving the MAT is the best way to minimize conducted engine heat. But, to keep from compromising the TUNE, one would want to do that before putting out the $$ to dyno tune.

Marc tuned my car with the sensor in the air horn and the TB bypassed. Because (in part) the TB/air horn temp is reduced significantly, I suspect the temp difference that might result from relocating it is reduced "a lot", especially at WOT. So, I'm not moving mine - at least not until I find a need to return to the dyno again. But, it would be interesting to know what if any advantage there really would be by relocating the sensor vs. leaving it where it is and bypassing the TB.

p.

[Jagdpanzer]

Our MAT sensor is construted like the one in this photo
http://turbomr2.com/MR2/HowTo/Engine_Upgrade/Rebuild/Images/ECU/MAT_Sensor_6238_small.JPG

As you can see the RTD sensor element extends into the airflow and is insulated with plastic from the brass body. My thinking is when the engine is at low throttle position the airflow around the element is reduced the sensor element picks up radiated heat from the surounding air horn an TB. However, at wider throttle positions there is more airflow around the element and the heat pick up is much less.

[XfireZ51]

Paul,

Not sure the MAT move really affects WOT directly. The pulse width calc for WOT
is based off of where the BLMs are prior to going into PE mode. The MAT sensor input will be taken into account by the ECM as it calcs the PW for closed loop. I am not certain whether the MAT sensor input causes the ECM to modify the calc'd PW for WOT operation although the table does consider airflow so it may.
However, all of that is "baked in" when you tune for WOT. The Intake Air Track model for intake air heating is obviously more consistent since it doesn't deal with the heat soak at the manifold. IOW, intake air temp doesn't change although the coolant temp(and so the manifold heat soak temp) can vary at the same intake air temp. From a performance standpoint, there probably isn't much difference between MAT/IAT. My sense is this was one of those "performance enhancements" like the Mid America TPS signal booster. Without the ability
to modify the calibration, these devices "tricked" the ECM primarily to richen the mixture. Once the vehicle begins to move, there's a smaller difference between the use of MAT or IAT will make.
I started looking into this because I noticed in colder weather, my AFR was running into the 13's with my coolant temp running at the 160s during cruise.
The MAT table in our cal uses a factor that supplies a modifier to the ECM
in the PW calc. This factor provides a term to the ECM that is a blend of Coolant and Manifold Air Temp. This table is based on the air temp. The resulting temp
term is then applied to air flow and finally the ECM modifies the PW based on that. The greater the airflow(higher speed) the less the coolant temp will affect the intake air charge.
Looking at the stock table, the higher the Manifold Air Temp gets, the less the coolant temp is considered and PW is reduced due to warmer air. However, coolant temp becomes a greater factor in what would be normal cruise coolant temps. I will try some new table values which reduces coolant temp input into the PW calc at those temps. See how that works.
Now just to add a little more confusion to it, the $8D mask (TPI CALIBRATION) is the calibration map the LT-5 calibration was derived from. $8D apparently has an option that allows use of values based on either MAT or IAT. IOW, GM had the values in the calibration already there depending on whether that particular vehicle used a MAT or IAT sensor.
Maybe Jep can tell us if the LT-5 cal uses the same option as the $8D. If so, we could just check or uncheck that option in the cal when we make the move.

Jep,

The $8D mask uses the Option Word 3, bit 4 for this switch.