Thread: Is your IAT sensor hurting performance? Find out here!

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I have trouble believing the PCM wouldn't be able to keep up with a fast changing sensor. I think the PCM is unbelievably fast.

I agree that we should have a faster acting IAT but...

It is still reading the air temp before it is compressed and heated by the supercharger (assuming you're boosted). How do we account for that?

Then to make matters even more complicated, say you are running an intercooler. Now wtf is the air temp the pcm should use to make the correct calculations?

I'm not a tuning whiz as far as knowing what tables we have but I'm working on it. However I'm wondering if we should zero out any air temp adjustments in our track tune except for very hot temps and scan for KR.

What do we care how fast our IAT reacts if the calculations it is used in are bogus becasue they are just guessing what is really going into the cylinder?

This thread makes me glad I use a double walled 4" FWI and don't see more than a few * above ambient in traffic.

the problem with the IAT is it's Thermal Time Constant. essentially how fast it reads. most GM IAT's are at least 15 seconds TTC. here's a bit of background on the Thermal Time Constant--


Thermal Time Constant (T.C.):
When a thermistor is being used to monitor the temperature of it’s environment then the accuracy of measurement of the resistance of the thermistor is critical.
While the power dissipated in the thermistor is an important factor in this measurement as discussed in the previous section, the thermal characteristics of the system and the thermistor are important also. This is especially relevant in systems where the temperature is changing with time. The dynamic thermal response of the thermistor must be considered in these situations. To quantify this dynamic response, the concept of a Thermal Time Constant (T.C.) is used in the thermistor industry and it is defined as follows:
The Thermal Time Constant for a thermistor is the time required for a thermistor to change its body temperature by 63.2% of a specific temperature span when the measurements are made under zero-power conditions in thermally stable environments.
This concept is illustrated in the example below:
Example: A thermistor is placed in an oil bath at 25°C and allowed to reach equilibrium temperature. The thermistor is then rapidly moved to an oil bath at 75°C.
The T.C. is the time required for the thermistor to reach 56.6°C (63.2% of the temperature span).
The dominant factors that affect the T.C. of a thermistor are: The mass and the thermal mass of the thermistor itselfCustom assemblies and thermal coupling agents that couple the thermistor to the medium being monitored.Mounting configurations such as a probe assembly or surface mounting.Thermal conductivity of the materials used to assemble the thermistor in probe housings.The environment that the thermistor will be exposed to and the heat transfer characteristics of that environment. Typically, gases are less dense than liquids so that thermistors have greater time constants when monitoring temperature in a gaseous medium than in a liquid one.
The definition of Thermal Time Constant arises from the exponential nature of the rate of transfer of heat between the thermistor and the medium that it is monitoring. It is similar in principle to the definition of time constants in describing the responses of systems where physical effects have an exponential response with respect to time.

The IAT is simply an analog thermal resistor. The IAT sampling rate is SOLELY a function of the input on the PCM. If you want to increase the sensitivity of the IAT, you will need an IAT pellet with a smaller thermal mass that can react quicker with the changing air temps. All said, I don't believe that the incoming air changes THAT fast...

Mr. Toasty, that is quite the block of information there and Im sure will help things along quite well.

I'm suprised most of you still have IATs.

I say screw em get rid of them and use a happy knob (connect to your original IAT harness) and be able to adjust timing anytime anywhere. Any vendor out there can put in the proper tables, or if you have a tuner you can set it up yourself. Its a very nice mod, sure beat lugging a laptop around everywhere.

IS the IAT really that slow? When scanning from a dead stop, my IAT's start dropping immediately and are ambient with in seconds.

Originally Posted by IndeedSS

and are ambient with in seconds.

And I think that is the point, seconds. Precious seconds. Seconds while you are trying to make your way to the big end of the track. Normal everyday street driving, probably not a major issue, though the more accurate and responsive the sensors are, the better all the way around the engine will operate in general.

Since timing is tied to IAT's I would think any improvement in responsiveness is a good thing in just about any situation.

Originally Posted by TDCRacing

but sometimes it's the little things that add up at the end

EXACTLY! Its all about the smalll steps. Its like th old question, would you rather have a million dollars now or a penny that doubles everyday for 30 days.

Sometimes you can eek out those larger than expected or normal gains, but for the most part, doing the little things step by step that turn into a big picture from the cumulative effect.

Isn't there a faster IAT for the GP's available? I know I've seen a write-up somewhere on this. Although when I did a cross-reference mine was the fast one, so I don't know. IIRC this write-up was on a GTO forum.

I think you may have seen that on the GTO forum. As for a readily available faster IAT, no there isnt one available. It would have to be a custom solution.

Originally Posted by Reptile

The GTO guys have one from Vector motorsports. That one runs right at $100.

This one is a variation on that design.

Ding Ding Ding...Vector is the one I was thinking of.