FAQ: Where to install the IAT (Intake Air Temperature) sensor...

The resistor tricks the PCM into thinking the intake air is cooler than the sensor reports, which commands a more aggressive timing table for more HP in theory.

It can work with cars where the IAT sensor is actually inside the throttle body or manifold, as the heat from the engine can interfere with accuracy. Another way to achieve this would be to move the sensor away from the TB, closer to the air filter.

Our engines depend on a more accurate reading because we are forced induction. The timing advance is critical to ensure safety against spark knock. That's probably why our sensors are mounted in a better location from the factory.

If you wanted the ability to control timing in that manner. You would want to look into Casper's Timing Commander. It's a neat gauge sized gadget that plugs into the IAT connector and effectively allows you to change your timing on a whim. It requires changes to the spark tables.

The downside is you are constantly changing the setting from morning to afternoon and night. I only use mine at the track. Otherwise..it's IAT for me.

AA wrote:

I think inside the filter or tube would be ideal. In the fenderwell would be okay. Try to keep the sensor as close to the filter as possible for accurate reading.

Curious as to why this is. Why wouldn't we want to sample IAT right before the TB? Wouldn't that give the most accurate reading of the temperature of the air that is entering the engine? I'm sure the air is warmer there than it is next to the filter.

Short answer - because of air speed. Air is moving so quickly through the intake, it doesn't have time to heat up.

Think about what's going on inside the air intake. It's not still air; it's moving quite fast. Our cars flow about 30-40 lb of air per minute at WOT, according to the MAF sensor. I have one scan showing 38 lb/min, which is about 550 CFM. If we take this value and calculate air speed running through a 3" intake, the velocity would be 125 MPH.

Yes, 125 MPH (this kinda makes RAM AIR seem like Pontiac marketing bunk, doesn't it?).

125 MPH = 660,000 feet/hour, or 2,200 in/sec. Now if we calculate how long it takes the air to move from the filter to the TB, or about 18", that comes to .008 sec. So at WOT, intake air moves from the filter up to the TB in only 1/125th of a second!

You don't need a physics degree to understand air temperature can't change much going from the filter to the TB in 1/125th of a sec, because it's moving so quickly there's not enough time to absorb significant heat. It's the same temperature as it passes through the throttle body and on to the blower. So the intake air temperature isn't any different at the TB compared to the air filter, because it's constantly being replaced by FRESH, COOL air (to be fair, there's probably some slight heating, but we're talking about fractions of 1º, probably hundredths of 1º.

But if you mounted the IAT sensor closer to the TB, your IAT reading will be much warmer. Why? Because heat from the engine, supercharger, and the coolant inside the TB will soak down the intake tube and heat up the IAT sensor from it's mounting location. It could gain +50º, even +100º hotter than the air it's supposed to measure. By keeping the sensor as close to the filter as possible (like the OEM set-up) and as close to center of the intake stream as possible, the PCM will see the most accurate intake air temperature.

Roger that. I also notice when I scan IAT that it doesn't change as dynamically as all the other fields I scan for. RPM, boost, fuel trim, etc. are all updated in real time. But IAT changes like once every 5 minutes. Maybe not that long but its slllllllllow to update.

Why is this? I would assume something was wrong with my scanning gear but I remember a thread you made, Aaron, about how you replaced the sensor with an omni sensor or something?

For reference here, do you know the difference in update speed between the OEM IAT sensor and the omni upgrade? If I changed my sensor to an omni would I get more/faster feedback on my IAT while scanning and also more accurate readings?

Mostly, it's because the temperature of the IAT sensor itself is impacting the reading, ie. heat soak.

There is this thing called entropy, which is the tendency of every warm object to transfer its heat to cooler objects (or fluids) in proximity to preserve an equilibrium. Also, cooler objects can absorb heat from warmer objects (or fluids) around it. The 2nd law of thermodynamics states that heat always transfers from warmer bodies to cooler ones.

So back to the heat soak issue. It exists, even far away from the TB. There is heat within the engine bay air, in the walls of the air box, and the intake tube. The IAT sensor absorbs some of this heat (it's cooler than the air box, as the intake air cools the sensor). Because the sensor is being "warmed", affecting its reading takes some time since the intake air now needs cool BOTH the sensor, AND the airbox. Eventually enough heat is pulled away from the sensor, causing its resistance to change, and giving a reading.

How do we get quicker readings? By keeping the IAT sensor as close to ambient temperature as possible, isolated from anything warm (other than intake air). Now, when the intake air gets hotter or cooler, entropy's job gets easier. The sensor's reading can change much more easily (quickly) without having to lag from heat soak. Or, the intake air has to work less hard to change the sensor's resistance, because it's only absorbing heat from the sensor, not heat sinking in from elsewhere (aka, 200º engine).

The Omega sensor is a specialized MIL-spec component, optimized for minimal heat soak effect and fast response time, but it must be mounted correctly for best results. Keeping the tip of the sensor in the center of the intake air stream is a huge plus. I usually see IAT changes update within 5-10 secs, but in come cases at WOT I've seen it report in as quickly as 3 secs.

Read about the install here: https://rivperformance.editboard.com/t8404-write-up-omega-intake-air-temperature-sensor-iat

This is interesting. Check out the location of the IAT on the INTENSE FWI, Right up next to the TB.

Quote :

INTENSE now offers a fenderwell intake kit that combines best of breed products such as a 9" K&N cone filter, a perfect fitting PCM tray, a custom molded throttle body adapter with molded in IAT hole, and our exclusive smooth walled intake tubing.

charlieRobinson wrote:

This is interesting. Check out the location of the IAT on the INTENSE FWI, Right up next to the TB.

Quote :

INTENSE now offers a fenderwell intake kit that combines best of breed products such as a 9" K&N cone filter, a perfect fitting PCM tray, a custom molded throttle body adapter with molded in IAT hole, and our exclusive smooth walled intake tubing.

maybe the display sample was assembled backwards, or maybe we can get a comment from INTENSE?

My guess is they sell it that way so the OEM connector will reach without the need for an extension. Or, flip it around at add the extension (prob $10-15 extra).

AA wrote:

My guess is they sell it that way so the OEM connector will reach without the need for an extension. Or, flip it around at add the extension (prob $10-15 extra).

...yeah - a biased but accurate reading could be adjusted for. A reading that drifts because of heat soak (and becomes both imprecise and inaccurate ) can not. I don't know if heat soak gives you only bias or both bias and drift.

Albertj

Are you suggesting the INTENSE FWI is a poor design? Sounds pretty lazy to put the IAT on the TB only so the OEM wiring will reach it. Why not include an extended wiring kit?

I would like to hear what INTENSE has to say about this. I am sure they have a good reason for it.

I will ask John at INTENSE and let you know what he says.

charlieRobinson wrote:

Are you suggesting the INTENSE FWI is a poor design? Sounds pretty lazy to put the IAT on the TB only so the OEM wiring will reach it. Why not include an extended wiring kit?

I would like to hear what INTENSE has to say about this. I am sure they have a good reason for it.

Not suggesting that it's a poor design, just saying I'd like to know why it is as it is.

Quote :

Are you suggesting the INTENSE FWI is a poor design? Sounds pretty lazy to put the IAT on the TB only so the OEM wiring will reach it. Why not include an extended wiring kit?

I haven't heard anything yet from INTENSE, but on the surface, this appears to be a simple marketing decision. Why not include the IAT extension? Because they can sell it for an extra $20: LINK

From the description:

"This 24 in plug-in harness extension allows you to relocate your Intake Air Temperature Sensor from the factory F-duct to a custom location of your choice. It is ideal for use with fenderwell intakes, cold air intakes, aftermarket air boxes, or timing modification devices that use the IAT signal for adjustment. 300 degree nylon convoluted tubing protects the wire from heat and weather and keeps your vehicle looking neat and clean. The engine end is heat-shrink wrapped for extra heat protection."

Look at what ZZP offers with their FWI kit (note position of IAT bung): LINK

Mandrell bent steel intake tube, silicone couplers, aluminum shroud, and and IAT extension. Price: $190



INTENSE is positioning their product much lower at $100. Entirely different approach - bare minimum product with the cheaper flexible tubing, and not as many pieces - it's just not up to the level of ZZP's product. It's a classic case of "you get what you pay for", and there's nothing wrong with that. I think some people expect to get a lot for $100. But considering CAI intake kits for every other car in the universe start at $150 and go up past $300, I wouldn't expect much more from the INTENSE kit.

I also found this interesting. It appears INTENSE supports putting the IAT sensor near the TB: LINK

My guess is that you want the IAT to provide the most accurate temperature possible for the MAF sensor, the temp actually going into the sensor. It's critical for proper readings from your MAF to know the air temp at the MAF.

Otherwise IAT is only used for certain timing modifications for extreme circumstances, and my guess is for that you also want to know the air temp at the last measurable place before air enters the throttle body/engine.

Maybe someone should try mounting their IAT sensor up close to the TB and report the temperatures they see. Could be it really doesn't matter as much as some of us think.

From John Rucker at INTENSE:

"We have the IAT integrated into our silicone throttle body adapter mainly for ease of installation and also to keep the electrics closer to the engine bay and out of the weather. On a street car, if you have a reasonably secure mounting point somewhere upstream of the throttle body, then in practice you should be in good shape.

The PCM has a two main ignition table for the timing – a high octane and a low octane. The IAT is used as a modifier for that base table. Here’s a pic to show them represented in HP Tuners for a stock Riv:



As you can see from the IAT table in the bottom right, in GM’s tune there is no modification to the stock timing except in extreme cases. When we’re tuning there are usually changes to this, but they’re also pretty minor. The rows for the IAT sensor input are also fairly coarse, so plus or minus 5-10 degrees of temperature at the IAT has relatively little effect on the tune. And since the biggest impact on a tune is at large MAF inputs, the exponentially higher flow of air negates heat soak from the location of the IAT as well. So in practice, the location of the IAT doesn’t matter too much as long as it isn’t getting dramatically heat-soaked from the engine. Whether the air temp is read from an IAT located in a silicone adapter near the throttle body, integrated into an inline LS-style MAF, or in an air box should have a very minor effect, assuming any change in timing at all.

For an all-out track car, I might move the IAT upstream a bit to rule out any potential timing shift, but I’d also be well into the tune at that point and would likely be running an LS-style MAF with an integral IAT. So that special case doesn’t really apply to a primarily street-driven car that need to handle much more varied temperature and weather."

Thanks to John for the detailed response. His points make good sense, and although I prefer to keep my sensor further upstream, I can see why INTENSE mounts the sensor where it is. It's just easier to install, and for the stock IAT table, it really won't matter much if IAT is reading a few degrees off (high). However, I forgot to mention my IAT table is modified, so it's much more important to keep the IAT readings spot on. I have the PCM starting to cut timing starting at 86ºF, and ramped up aggressively from there. I do this to protect against knock when the intake air is hot. If the air reading is too warm, it would cause the PCM to unnecessarily pull power in my case.

Now we know!

I was messing with the airbox and sensor when I was replacing my headlight bulbs..

How the heck do you get the sensor out of the airbox? It looks like it twists and locks but it wont budge and it looks like its plastic welded to the box?!

What's the deal?

It's a bayonet mount. Twist it.

AA wrote:

It's a bayonet mount. Twist it.

Either I'm a wussy or this thing is jb welded in. There's black goop around the seal point. I will twist harder and see what happens.

I tried all manner of things to get the dang thing out when I was ditching the stock box. Ended up having to just more or less cut it out of its mount. Was crazy stuck in there

llamalor2112 wrote:

I tried all manner of things to get the dang thing out when I was ditching the stock box. Ended up having to just more or less cut it out of its mount. Was crazy stuck in there

That's what I'm afraid of... I really dont want to have to cut it out.

Here's what the airbox looks like after the IAT sensor is removed. You can see the two slots that engage the bayonet tabs:

Thanks, AA. Looks similar on mine except for the plastic weld around the seal. I am prepping for my 4" intake so I wanna make sure I can get the sensor out clean first.