94bird

I've always been curious about this mod given that the sensor is in a rubber hose which has VERY low conductivity of heat. If the sensor body outside of the hose really heats up that much and skews the readings wouldn't the simplest solution be to just wrap the outside of the sensor with some of the heat shielding that's so readily available?

shoebox

You could simply do the same tests with some different resistors to change the perceived temps. Remember the IAT resistor trick that people started doing years ago? I tried it. I had no way to gather data at the time, but I could not tell one bit of difference between the resistor and normal. That's one reason for my skepticism.

97ta9

I don't think you will notice much horsepower if any at all. I did it as a drivablity mod, because on a hot day sitting in traffic my car would hesitate a little of the line, after relocating the IAT it no longer hesitated a little off the line sitting in traffic. Shoebox I completely understand what you are saying, and thats why I wondering if Madwolf or anybody else who has programming and tuning experiance knew how much the IAT reading effects things.

camzaro28

i am not saying i want to do this to gain hp! just figured if it helped the motor run better i would want to do it! from what i have read, i guess i will do it! if i notice my car running worse i will put it back to stock! thanks alot

95WhiteTA

I had to relocate my sensor to the airbox when i switched to ram air, and it actually seemed to run worse for a little while, but my PCM must have "learned" a little after the change, because it ended up smoothing back out.

94bird

Relocating the IAT sensor will tell the computer the air charge temp is lower than it truly is. This will result in a different value being used for air charge density and thus will likely result in a change in spark advance and fuelling. When the IAT gets hot the ECU will put less fuel into the cylinder and retard spark. Both of these changes, plus a hotter intake charge temp can easily result in what you experienced as a stumbling off the line. By moving the sensor you effectively kept a little more spark advance and a little more fuel, and thus most likely made a little more power. You could have achieved better results by just lowering your intake charge temp in the first place, such as running a cold air intake and lowering your underhood temps (cooler thermostat, lower fan turn-on point, venting the underhood air, etc.). Then you get your fuel, spark AND cooler intake charge. Relocating the IAT does not fix the root cause of the problem, which is a hot intake air temp.

I initially thought relocating the sensor was meant to solve an erroneous reading since the sensor might be getting heat soaked from the outside underhood air, but after looking at it much closer I just can't believe this to be the case.

Injuneer

IAT is not used for fuel calculations in the MAF 94+ cars. The MAF needs to know the air temp, so it can heat the wires a fixed number of degrees above the incoming air temperature, but MAF measures air temperature internally. Yes, IAT is an important part of calculating the air density in the speed-density 93's, but not in the MAF cars.

The speculation is that there are hidden table in the PCM that alter spark advance based on IAT reading. That would make sense... I do it with my aftermarket ECU. There is a mysterious 3deg of advance that shows up in scans, that can not be accounted for with the "normal" spark timing tables. On the other hand, the guys that develope LT1_Edit did a simulation, trying to vary the IAT value and measure the affects on PCM output, and couldn't find anything.

If the sensor is heat soaked, it is not accurately reporting the temperature of the incoming air. I found the same problem in very hot weather, stop 'n go driving.... the IAT would reach 145degF, and I sensed the "hesitation" coming off idle. Engine seemed to idle a little rougher also. I found that after relocating the IAT to the cap on the K&N in my Honker CAI, the hesitation went away.

I don't think there's significant HP here... just the perception of a smoother running engine. And, if you run a ScanMaster, you end up with a more accurate outdoor air temperature monitor .

94bird

So, how do you know it's not accurately reporting your charge air temp? I've seen other similar applications where there is indeed that much of an increase in charge air temp and more in just a couple feet of rubber hose at idle. That's why until someone proves me wrong, I would side with the IAT reading. Just today I doublechecked an IAT in another vehicle that was registering 150 deg. F IAT with a 65 deg. F outside temp. A quick insertion of a thermocouple probe into the rubber hose next to the IAT sensor immediately read within 5 deg. of the IAT sensor reading. My LT1 is getting an engine rebuild right now or I'd just try it on mine too.

Thanks for the clarification on how the LT1 ECU deals with fuelling in MAF cars. The spark retard will be a much larger influence on what you felt though.

Injuneer

I've done the same thing with a remote temp sensor, and found heat soak to be a problem with the stock LT1 elbow, when I had the stock setup. Interestingly, it doesn't seem to be as much of a problem with the WS6 airbox, which I have insulated from the radiator cover. It was important to me to verify the accuracy of the IAT, since my engine is running open loop, speed-density on a MoTeC M48Pro ECU.

I even threw in an extra IAT sensor, so I could monitor it off the stock PCM with my ScanMaster.

http://cjcfo.fbody.com/members/injun...A/DualIATs.jpg

There also an extra coolant temp sensor in the photo, monitoring the temperature of the coolant returning from the steam tubes at the back of the heads. Can't have too much data.......

kevm14

Those who want to do this with the stock PCM still controlling their LT1 might have success using the Y-body oil temp pin. Not sure if the impedence range of the oil and coolant/iat sensors are the same though.

97ta9

Thank you Injuneer, for clearing up a few things. I allways wondered how much the IAT value affects things, because looking at tunercat and lt1-edit the IAT value isn't really a variable in engine management. Do you think that people using the stock computer whould see a mysterious 2-3deg of advance relocating the IAT. Does anybody know for sure if their is a hidden IAT value table in the stock PCM or is that just speculation. 94 it was not knock retard I was feeling, because I have no knock retard before or after the IAT relocation. I was running a cold air intake and bypassed t-body coolant lines and all the other stuff. I did notice that using an infared thermometer the intake manifold does heat up more at idle in hot weather, but common sense would dictate that. Is there any way to reduce the heat soaking affect of the intake manifold, other than spraying nitrous, or putting a bag of ice on it? I remeber reading a thread about jethot coating the intake manifold, but I don't know if that would help.

unvc92camarors

if you jethotted the intake that would just keep the heat in correct?
doesn't that make for even higher intake air temps?
although it would keep the underhood temps cooler probably, it would still hurt you incoming air right?

94bird

Thanks for doing the experiments Injuneer. How much difference in IAT from the sensor vs. your thermocouple did you see? I'm curious how heat soaked you found the sensor to be. I have never found this to be an issue in any other car, even when running hot tests in Vegas or Arizona in the summer.

For those of you talking about insulating your intake manifold, et al, the answer really is to just get the heat out from your underhood more effectively. All your underhood components will be happier.

94bird

I'm not talking about knock retard. I'm talking about a preemptive strike against knock. With a higher IAT, the calibration should take out spark without seeing knock. It's done in all the cars I've worked on.

jdizzell

The IAT will help during closed loop. So if your running at the track, pcm doesn't use the IAT for fuel calculation.