Topic: So what's everyone's thoughts on this performance mod?

[oHIobellboy]

As long as the plastic is thick enough to hold the sensor under boost, I think it's a good idea and worth a try.

What did I do with that duct tape.     

[MyBigToy]

What did I do with that duct tape.     

No need for duct tape - the boost is made post-throttle body on the Magnacharger. But it doesn't really matter as the plastic is plenty thick.

Mick - that's the wrong side of the tube if it's going on the side.

[Richie_Rich]

No need for duct tape - the boost is made post-throttle body on the Magnacharger.....

I'm an idiot.
I knew that.
I'm used to turbos these days.

[Main One]

Where do I begin on this????

I've done mucho consideration on effects of IAT on my Long Term Fuel Trims (LTFTs) for about a year after seeing how much affect changing ambient air temps were having since I relocated my MAF and IAT sensor due to my ram air setup.


MBT, I would suggest you consider several things before you take this plunge.

1.  If you did move your IAT sensor, you would want to move it downstream from your supercharger so that your computer calculations were taking into account the effect of your supercharger and intercooler.  In your setup, IATs anywhere upstream are rather anecdotal no matter whether or not they are subject to heat soak.

2.  Assuming that there is a fair amount of heat soak (and I believe there is some heatsoak affecting the stock IAT measurement), how much timing is being pulled?  Looking at the stock tune that came with my 03 (just the IAT spark base and multiplier tables), it is less than 2 degrees per 10 degrees increase of ambient temperature.  If you can get a good handle on the temp of the air actually flowing through the heads, that would be a good thing to use to adjust timing.  However, I don't see this kit as being intended to be installed either in a head or the intake manifold.

3.  Besides spark, among other things, IAT is used to calculate airflow when the computer is supplementing the MAF readings with the calculations done using the manifold pressure sensor in conjunction with the volumemetric efficiency table.  It is these readings which have captured a great deal of my attention for most of the last year.  Besides using airflow to determine how long to pulse the fuel injectors, calculated airflow for each cylinder stroke is another input to how much timing your spark plug is going to see.  Having stable LTFTs indicates you are giving stable inputs into other calculations affecting timing.

4.  Since the stock location of the IAT sensor is far from being located in an ideal, or near ideal, location, GM has put in place a way to hedge against the problems caused by this through the Cylinder Charge Temperature Bias vs Airflow table.  In a stock configuration, it is highly unlikely that the intake air will not increase in temperature after passing through the MAF.  The intake tube passes along the top of the radiator, and has appendages down behind the radiator as well.  The air is also likely to pick up some heat in the intake manifold as well.  The bias table adds to the IAT reading a percentage of the difference between the IAT reading and the ECT reading, anywhere from 0 to 200%.  (A value of 100% would therefore basically just be using ECT as the input air temperature.)  At idle airspeeds, the stock table is going to be causing the computer to calculate airflow a little bit closer to ECT than to IAT.  (Bias value greater than 50%.)  From idle to higher airflows, this table slopes down to about 25%.

For example, let's say you are driving on a nice 70 degree day.  Your IAT readings are at 80 degrees.  Your ECT is at 200 degrees.  When doing dynamic airflow calculations, the computer is assuming, at idle that the actual air going into your cylinders is about 150 degrees.

With my IAT sensor located much closer to the throttle body, I have found that I need to really cut down the values in this bias table to get my airflow calculations to be stable.  At idle, my engine computer is using a bias value of around 30%, such that in the above scenario, the actual air going into my cylinders would be calculated at about 116 degrees.

Now for why I believe in external heat affecting the stock IAT sensor.  Keep in mind, I am using a JET MAF/IAT sensor (thank you KY_Bob), but it is rather similar in regards to the stock sensor.  Unlike the stock bias table, which when plotted looks rather like a hockey stick, my table when plotted looks more like a scythe.  My table bottoms out at 20 g/sec of airlow (about twice idle airflow) to 11.4% (44.3% stock), ramps up from there to 60 g/sec to 18.9% (35.9% stock), and then is pretty stable in the 18-19% area for the rest of the table.  The only theoretical reason I have for my table to "dip" is due to the sensor picking up some heat from the radiator, which is only a few inches away, and for this affect to be greatest (in a relative sense) during low airflow conditions.

Anyway, I've worn my fingers out, and giving you hopefully some good, as well as hopefully understandable, information.  To sum up, here's my bottom line on this mod:

1.  I wouldn't bother on a boosted application unless mounting post turbo or sc and intercooler.
2.  I wouldn't do this mod without custom tuning.

M1

[MyBigToy]

As usual, Main One is a wealth of information and food for thought. Once again, I would not install this mod without due consideration to tuning. I'm going to get serious about tuning after the 3.25" pulley and cam go in.

[oHIobellboy]

<------  is reading all this and trying to soak it up.