Air Temp Relocation Kit

[32valvZ]

Is it worth the time to put one in? Any real advantages? Will the prom need recal again?

Thanks!

[lfalzarano]

Marc has a write up

http://www.zr1specialist.com/HAT%20Web/products/air%20sensor.htm


Sent from my iPhone using ZR-1 Net Registry (http://r.tapatalk.com/byo?rid=90383)

[We Gone]

I have mine relocated to the air intake box as it passes over the radiator. Any results on how this effects or differs from mounting at the front of the vehicle ?

[-=Jeff=-]

I have the air temp relocation kit I will probably never use.. Let me know if you have interest and I can dig it out.. It is brand new

[XfireZ51]

If u relocate the MAT (Manifold Air Temp)to say the radiator shroud or somewhere else, you are “converting” it to an IAT (Intake Air Temp) sensor. This is done due to the heat soak of the sensor that occurs by the plenum and air horn. When u look at the calibration, there is a table that applies a correction factor to the fueling in order to compensate for the air temp and keep the fueling consistent. The table tells the ECM how much or the ratio the ECM should consider between Temp and Air Temp. When u move the sensor, that table is now incorrect. Looking at the values in that table, it assumes your typical operating temp range is going to be ~ 80-110C or so. Your now relocated sensor will NEVER see those temps. And so the ECM will adjust fueling based on what are much lower temps using those adjustment numbers, ie motor will run richer.
So, in order for the now IAT to properly provide more accurate input to the ECM,
that table needs to be modified for the temp values the ECM will be seeing from the IAT. That means, as in my case, the ECM will see temps down in the 8-40C range typically. So the values there need to be changed in order for the ECM to properly compensate for intake air temps.
Could u adjust VE tables instead to compensate? Yes, but the minute the intake air temp varies from the one u used in adjusting the VE table, the fueling will be off.
The intent of this compensation is to apply a factor to the base VE table taking into account now the temp of the air. Why? Because the correct fuel is based on the mass of the air the motor is taking in, which temp affects.
As air temp changes, air mass changes, and so amount of fuel must be adjusted for that mass.
You can see this as u sit at idle and intake air temp rises. The key is to have ur compensation table set up so u continue to record a consistent BLM as intake air temp varies.
Bottom line, no sense moving MAT unless u modify the compensation table, IMO.

[WARP TEN]

I don't know if Marc alters the tables, Dom, but I do know that one of the first modifications I did on the '93 was to move the sensor to the plastic part above the air filter. On the '95 Marc moved it to his preferred location in front of the radiator. He says the higher temps cause the engine to pull spark, costing about 10 HP and 10 ft lbs TQ. I am not sure I could tell the effect of changing the location but it always seemed sensible to me based on info I had at the time. --Bob

[We Gone]

Marc made the adjustments to the tables with mine located to the plastic part above the air filter.

My question for anyone who knows>

I have mine relocated to the air intake box as it passes over the radiator. Any results on how this effects or differs from mounting at the front of the vehicle ?

[XfireZ51]

Marc made the adjustments to the tables with mine located to the plastic part above the air filter.

My question for anyone who knows>

I have mine relocated to the air intake box as it passes over the radiator. Any results on how this effects or differs from mounting at the front of the vehicle ?

That’s where mine is located also. And yes the sensor does affect timing, throttling it back as temps rise.
I have mine in the same spot so that it more accurately mimics the intake air temp as the motor sits there for instance during idle. When I datalog I can track the change in intake air temp w that used for outside air temp indicator on the AC controller.

[Paul Workman]

Well, here's a twist for the dicussion: Coolant bypass affect on the air temp sensor located in the stock position.

Case in point, after bypassing the TB, coolant does not heat the TB and the horn directly in front of the TB. In fact, you can lay your palm on the plenum with the engine running and it is quite cool w/o the coolant running through the TB.


Thoughts on that, Marc or Dom?? Does bypassing the TB make moving the sensor unnecessary??

Off Topic, but also related to plenum temp: Consider the affect the cooler plenum temp has on the critical DIS module and its life expectancy, being that it is heat syc'ed to the plenum...

[XfireZ51]

Well, here's a twist for the dicussion: Coolant bypass affect on the air temp sensor located in the stock position.

Case in point, after bypassing the TB, coolant does not heat the TB and the horn directly in front of the TB. In fact, you can lay your palm on the plenum with the engine running and it is quite cool w/o the coolant running through the TB.


Thoughts on that, Marc or Dom?? Does bypassing the TB make moving the sensor unnecessary??

Off Topic, but also related to plenum temp: Consider the affect the cooler plenum temp has on the critical DIS module and its life expectancy, being that it is heat syc'ed to the plenum...


Paul,

IIRC, the coolant thru the TB was for icing in cold weather. Relocated MAT sensor will typically see air temps in the 15-40C range which isn't close to the coolant operating temps of 80C+ w a stock therm. And I seriously doubt the TB is as cool as 15-40C at operating temps.

[Marc Haibeck]

My strategy for the inlet air temperature sensor is to improve its operation when the air temperature is rapidly changing. Especially in a drag racing situation.

I have not observed the fuel trim changing significantly with respect to engine inlet temperature. At light engine loads the oxygen sensors have great authority over the AFR. They set the AFR.

At a stop light or at the starting line at the track the sensor in the OE location is measuring the temperature of the plenum. Maybe 150 degrees F. When the car starts moving, by 20 mph or so the plenum is flooded with ambient temperature air. Maybe at 75 degrees F on a nice summer day. The air is going so fast that it picks up little heat from the plenum. The air going into the cylinder heads is nearly at ambient temperature. Meanwhile the air temperature reported by the sensor is only a few degrees below the 150 degree plenum temperature by the time the car gets to 20 mph. Mounting the sensor in an area that corresponds to the temperature of the air going into the engine provides a more accurate engine inlet temperature when the air flow is rapidly increasing. With the sensor in the OE location it can be observed that the air inlet temperature being reported to the ECM is at about 120 degrees when the car is halfway through the quarter mile going 70 mph. At the same time the engine is consuming air nearly at the ambient temperature.

The OE calibration retards the spark 3 degrees when the inlet air sensor is reading 150 degrees F. This is a horrible way to start a drag race. With a relocated sensor I retard the spark 1 degree at 90 degrees F. I figure that if the ambient temperature is 90 degrees or more you are probably not looking to set a new personal record that day and it's better to protect the engine from detonation.

[Paul Workman]

Thanks Dom n Marc 4 the info. It helped me to "fine tune" my understanding - the cause/effect placement of the sensor has. Tho I seldom drag race since the group we raced at US-41 got tired of the FBI winning the team trophy, year after year and quit inviting us to come play (kinda like the SCCA, huh?):-({|=:sign10:

[XfireZ51]

My strategy for the inlet air temperature sensor is to improve its operation when the air temperature is rapidly changing. Especially in a drag racing situation.

I have not observed the fuel trim changing significantly with respect to engine inlet temperature. At light engine loads the oxygen sensors have great authority over the AFR. They set the AFR.

At a stop light or at the starting line at the track the sensor in the OE location is measuring the temperature of the plenum. Maybe 150 degrees F. When the car starts moving, by 20 mph or so the plenum is flooded with ambient temperature air. Maybe at 75 degrees F on a nice summer day. The air is going so fast that it picks up little heat from the plenum. The air going into the cylinder heads is nearly at ambient temperature.

Marc,

The relocation of the MAT sensor was an old trick, like disconnecting the battery cable just before coming to the line. Both were bandaids when not much was known or could be done about modifying the calibration.
Disconnecting the battery cable was done essentially to reset the BLMs to 128. Why was that necessary? At a BLM of 128 or below in Closed Loop, the ECM does not modify the commanded AFR in PE mode. GM used this strategy as a means of protecting the motor from possibly running lean when in PE mode since the O2 sensors(which are narrow band) no longer affect the fuel delivery. When the ECM enters PE mode, it takes the last BLM closed loop reading prior to entering PE and modifies the fuel calculation for Commanded AFR based on that last BLM.
So if ur BLM just prior to entering PE is 133, the ECM considers that lean, and so applies an additional modifier to the Commanded AFR calculation, richening up the mixture to “make up” for the lean condition and thereby protecting against detonation. Disconnecting the battery results in the ECM not changing the commanded AFR calculation since the BLMs reset to 128.
Yes the O2s are there to modify fueling but depending on them to bring the BLMs into proper range isn’t the right strategy. The objective of tuning is to get the base parameters to as correct a point as possible thereby minimizing the intervention by the ECM. IOW, u want to get the BLMs in as close a range of 128 as possible so that there is little need for ECM correction.
While ur sitting at the line or coming up to it at a drag strip, airflow to the plenum is lower, giving it more time to heat up as it passes over the radiator and as it picks up heat from the asphalt.
Without a properly adjusted IAT compensation to maintain BLMs in the proper range, the ECM will likely see a BLM that would cause the ECM to introduce an adjustment to the Commanded AFR when entering PE mode.
Launching off the line, coming out of closed loop and having entered PE, the IAT and O2s no longer modify fueling. Its pretty much left to using the VE table and the correction factors applied for Commanded AFR in PE model. So ur WOT AFR, may in fact not be what would be considered optimal, but just safe.

[Marc Haibeck]

Dominic,

I use a wide band oxygen sensor tune the WOT AFR for 12.4 from 2000 rpm to 5000 rpm. Then 12.6 from 5000 to 7500. I like to stay on the rich and safe side.

[tpepmeie]

I have concluded that GM understood the MAT sensor behavior in the factory location and compensated for it in the calibration. The table is "F26 INVMAT MAT FACTOR VS. MAT". This modifies the air charge density based on the MAT value. What's interesting is that the OE calibration doesn't match the true physical air density calculation. It has approximately a 10% offset.

In the attached graph, the blue curve is the mathematical air density curve. The Orange curve is the OE calibration. Horizontal axis is air temp. Aside from some obvious high air temperature protection built-in (the dip after 56C), you can see the OE curve is approx. 10% under the real curve. The grey curve is the physical curve minus 10%. Fits remarkably well with the OE curve.

Edit: the OE cal richens the mixture, which make sense if the true air temp is cooler than being reported by the MAT sensor.