I was playing yesterday with my Autotap and was watching the IAT reading while idling in the yard.........

On a good cool air system IAT ought to be the same as the ambient air temperature..........mine rapidly climbed to about 115 in 72 air with motor at about 180....still climbing when I shut her off.....

I need to look at this some more under various conditions, but has anyone watched theirs under various conditions...i.e. highway, city, idle, track, etc.....

Hot air equals lost power!!!



BTW I have the SLP triple snorkle intake system

 

115 is a bit high, I see 106 occasionally.

Whats cool is when you have alky injection and you spray a 2 second burst and the intake air temps drop 30 degrees.

 

I run an IAT relocator in my Vette, and in my previous LT1 Trans Am...

I noticed that the IAT temp 20 minutes after shutdown in the summer would read 160F+... It also always seemed to take a little more time to crank over when hot, even when new...

After relocating the IAT, the car would fire up immediately from a hot start... I'm not sure how the IAT sensor was being used at start-up though, so I can't explain it...

One side effect I noticed on both the Vette and the TA, was an approximate 1 MPG drop in fuel economy with the IAT in constant cooler/cold air... I'm guessing that the PCM must be calibrated to take into account the artifically higher IAT readings from the stock location...

 

EXACTLY!

The IAT is a thermal resistor, or thermister(or?) It's resistance changes based on the temeperature. As such, apply a set voltage, measure the current, you have your reading. As the air heats up moving through the intake ducting it becomes less dense. Less dense air has less oxygen and thus requires less fuel to burn at the most fuel efficient ratio. With this in mind you want your IAT to be as close as possible to the point where the fuel is actually injected! If you locate the IAT further forward it will most certainly read cooler air and make the computer add more fuel. The problem is that by the time the air actually makes it into the engine it has gotten warmer and less dense. Effectively your car will run richer than it was intended. In theory your oxygen sensors will register this and the car will correct itself, but why go through the extra work? The ECM was calibrated for the IAT to be in the stock location!

The arugment that people make is that the IAT is so close to the engine that it gets heat soaked by the engine and it fools the computer into thinking that the air is hotter than it is. This really is complete crap. At idle this might be the case, but at wide open throttle the air is going to be moving through that duct work so fast that it will easily negate the "extra" heat placed into it by the engine. Think about it this way, take a steel rod and constantly heat one end of it while pouring ice cold water over the other end. Does the end of the rod in the water stream ever get too hot to touch? Not likely. It may get warmer than it would otherwise, but not signficantly. Whatever the difference may be, the effects of it are already programmed into your stock computer.

Relocating the IAT will make your engine run richer, which may or may not help you make more power depending on any modifications you have done to it. Any way you look at it though it is cheap modification designed to trick the computer rather than tuning it properly. If you need the car to run richer, program the computer so that it runs richer, don't try to fool it. Your car will thank you for it and you'll learn a lot more about how they work in the process.

When I think about all the money wasted on performance gimmicks such as these I really have to wonder if I'm in the wrong business.

 

But my original question was more directed toward using the IAT in its stock position as a basis for evaluating my intake system........not really changing the IAT

On a good CAI system the air temperature, as read by the IAT sensor, should be very near outside ambient......just wondering how mine compared to others....

I was not very pleased to see mine climb like it did at idle, but I need to look at it some more.......

Have you watched yours?????

 

I've never particularly paid attention to it, I do have some data logs at home that I could pull up.

I think a lot of the problem is that our air intake systems still draw air from under the hood, there isn't really a direct air path from outside into the air filter regardless of which system you use. The only difference might would be the ram air or vortex systems that actually go through the radiator shroud and pull air directly from there. Even then though it would probably only make a significant difference at high speed.

 

Interesting article in the current GMHighTech magazine about intake systems & how to keep the intake air cool........

Also some other recent articles suggesting how significant air intake temperature can be on power.......

I am thinking how to get cooler air & keep it cool........no easy way...???

 

 

A functional ram air system will certainly do the trick at high speeds. Most any system is doomed at low speeds, the air just simply isn't moving fast enough to remain cold. Ambient engine heat kills you before you ever get it under the hood.

You might try something like this

http://members.***.net/sr20defreek1/crxofdeath.jpg

 

 

During my last scanning session the highest reading from my MAT (manifold air temperature) was 94*f, that was after idling on the driveway for about 30sec's and coolant temp at 200*f.
Ambient air temperature that day was in the 70's.

 

If the "ducting" were built to insulate the air and itself from motor heat , it should work at most speeds, maybe even idle. System needs to include reflective shielding to prevent radiation heating.....

Part of the solution probably has to include keeping underhood temperatures down....

 

Agreed. Even if it were well insulated though it would likely eventually still heat soak, it would just take longer. Programming your fans to come on sooner can keep your underhood temps down significantly. If you have headers, ceramic coating helps a lot. I wonder if you could ceramic coat your intake to try and keep the heat in the intake rather than under the hood? Then again that might be counter productive.

 

The intake itself should be insulating material as much as possible.....such as plastic......new technology includes "plastic" intake manifold.......plus a radiant shield to reflect heat away from the intake.....plus an intake located to start with cool air, not underhood air already heated.....



C4Crazy787.......that is what I am talking about.......94 air when it is only 70 outside........need to get 70 air into engine NOT 94 air.......I saw mine climb to 115......NOT good for performance

 

Ok, I just happened to think about it so I've looked at some of my data logs. As long as the car is moving IAC temperature is VERY stable and largely independent of engine temperature. This confirms my theory that the air moving through the ducting keeps the IAC cooled to the point of reading consitently.

On thanksgiving day 2004 I made a very long datalog, 3368 seconds, do the math that is little under and hour. Unfortunately I do not really know the ambient temperature when I made the data log, but I could probably estimate it pretty good based off of my data.

I started the data log before I even started the car. With the key in the ON position I read an IAC temperature of 66.4 degrees. I would have to consider this the ambient temperature of the car / garage as the car sat there overnight. Engine coolant temperature registered as 61.3 degrees. 5 degree difference between two devices of unknown uncertainty is probably acceptable. Oil temp registered 51.1 I started the car and backed out of the garage and went about my way. Within a minute the engine coolant temp had risen to 74.8, oil to 53.2, and IAC had fallen to 63.9. I didn't get on the car very hard at all, I just drove normally.

At this point I'm just looking at the data log graph. Coolant temperature climbs and levels off at some 185 degrees after 540 seconds. At this point the IAT reads 47.1 degrees, oil is still climbing at 156. Oil temp eventually stabilizes around 190 degrees, the IAT stays at approximately 50 degrees and barely fluctuates for the next hour. It only begins to rise, getting all the way up to 55 degrees when I had to slow down and drive at relatively low speeds to get back to my house and park the car. Unfortunately I do not really recall the ambient air temperature on that day, but it wasn't all that cold I don't believe. The IAC temperature was probably actually pretty close to ambient temperature.

What this doesn't show is the effects on IAT temperature of idling in traffic, being Thanksgiving day the roads were empty, I drove for nearly an hour and only really had to slow down and stop when I came to the few intersections that formed the circle that I drove. If you would like I can data log my trip into and back from work tomorrow. That would be a lot more stop and go which might tell you more of the infomration you are looking for. I could also pay attention to ambient temp.

 

My IAT showed 132F couple weeks ago in a Datamaster logging session. Sensor in stock location and unmolested. Can't rememebr the ambient outside air temp but probably around 72 F. Engine was at operating temp, about 196 I think. My air cleaner lid is stock except for baffles removed (still has the shroud over the baffles area) so she was drawing her intake air from the engine compartment.

 

If Vararam would ever get off their butts and bring their claimed C4 Vararam ram-air system to market, we could all breathe a little cooler air...

And then there's http://www.corvetteramair.com

Only vulnerability I see with the ram air scoop is that while driving behind another car in the rain and the car up front is making the fine road spray, that nifty ram air system becomes a ram-water-spray system...

 

Was this with the car moving, idling, or ??????

 

I just data logged my drive in to work. Ambient temperature was 68*

At cruising speeds my IAT showed 75* When I had to get into the stop and go traffic it did finally get up to 88* while I wasn't moving. No doubt it would climb higher and higher if I just let it idle.

As an interesting side note I was driving down one of the last streets before I got to work and it was hanging aroun 88* I had been idling some before I got on this street but I wasn't really moving quickly, in fact TPS position was 0% as it is a downhill grade, IAT stayed at 88. I turned onto another street and thought I would see if I could drop the IAT, I put the car in second gear and eased into the throttle. The road was wet so I didn't want to go wide open, the maximum RPM I hit was some 4800 RPM's. In the time frame of 8 seconds I dropped the IAT from 88 to 82 degrees, I never exceeded 42% throttle.

This would lead me to believe that in a true wide open throttle situation your IAT would fall dramatically and very quickly. If you think about 8 seconds from a drag racing standpoint that is an eternity, but I don't really drag race at half throttle either. I can't help but feel like if you were really racing your IAT would fall to very close to ambient temp by the time you got out of first gear. Heat soak in the intake ducting is a fact of life that I don't think there is a lot we can do about. I just have to feel like that at wide open throttle though it doesn't matter so much. I mean you really only need maximum horsepower when you hit the throttle all the way down right?

There is a lot of time and money that could be spent to try and insulate the air intake and fabricate a better cold air kit, but I just really have to wonder about the how much gain you would actually see from it. Looking at my data I would have to say that any power gains would likely be very small.