Define: "Various reasons"

Oh and "Heat picked up from piping before TB" - nope, this is bunk, so don't even try to use that one.

 

it makes sense to me to put it on the elbow and put it in some kind of nylon tap like garfinkle did. can anyone think of some kind of plastic or nylon that i could put into the elbow and then put the sensor inside of that? its not the metal that needs to touch its the soft projection inside that needs to feel the air right?

why would people go get that new sensor if its pretty much the same reaction time.

 

Just to chime in, the nylon insulation in the sensor bung isn't necessarily a good idea, and here's why: when you look at thermal systems, what you're interested in is things that have a) high heat transfer rates and b) low thermal intertia. The aluminum in the UIM has a fairly high transfer rate, but also large intertia due to the thickness of the material. (In this case, the issue is the volume-to-surface area ratio which is poor; once the UIM gets hot, it doesn't cool down.)

So optimally you want the sensor in direct contact with something that will heat up and cool down rapidly with the change in air temperature--namely, a very thin-walled metal structure. This is why mounting it in an IC outlet tube is a good idea, because the temperature of the tube will more or less be equal to the temperature of the air and not the engine bay temp. (If you don't believe this, drive you car moderately hard and then quickly touch the inlet and outlet tubes of the IC. Don't get burned!...you'll see that their temp uptream and downstream of the IC is dramatically different. However, regardless of what's going on, the UIM is essentially the same temperature...)

The problem with nylon is that it insulates the sensor. This approach would be good for keeping the sensor from heating up, but once it gets there you have the problem that the body of the sensor can't conduct heat through the nylon. You're basically putting the sensor inside of a thermos--it takes a long time to get hot, but it also takes a long time to cool down. Since the whole point of replacing the sensor is to fix the slow-acting nature of the stock AIT, insulating the sensor will have the opposite effect. Perhaps in the stock location this is a good idea (to stop heat transfer from the UIM to the sensor) but in a relocated setting this is actually counterproductive.

-ch

 

who said that?

--- In Datalogit-FD3S@yahoogroups.com, "ennowein" <ennowein@y...> wrote:
> I'd say reasonably close, as stated I held both stock and
> new unit in ice water and measured both resistances
> (after waiting FOREVER for the stock unit to adjust ...).

sounds like substitue has much faster response.

 

great input guys. I didnt realize that the metal threads of the sensor had anything to do with how it should get its temps. That would be measuring the heat of the metal which should be the same as the air except for when it gets heatsoaked it will be hotter than the air is for a little bit. Are you sure about this? dont you want to strictly measure air temperature and not at all the temperature of the metal? I think the ideal would be to have the sensor suspended in the middle of the post intercooler pipe. but I guess thats not possible.

I guess he was saying the ohms were similar not the reaction time.

 

stock sensor. cracked thread shows what looks like a "thermowell" ...long hollow tube with rounded end where sensor is placed inside. no wonder gm sensor, with exposed element in tube ports, has faster response.

http://www.alexwan.com/rx-7/journal/...0/feb10_15.jpg

 

That "well" has always felt and appeared "fiberous" (i.e. nylon or plastic) to me anytime I've examined the sensor. I cannot imagine it providing a high heat transfer rate.

Quite simply it just looks like a lame design and physical placement in the OEM EFI system.

MoTeC sells various IAT sensors that I know can be adapted as well. What is important is that the temp->ohm graph is similar to stock unless you specifically tune your aftermarket ECU to compensate for a difference.

That being said, mine is relocated to the outlet tank of the stock IC and I see a fairly fast response following heat soak. I've seen 10 degree drop in 15-20 seconds @ ~50C starting.

 

mine drops like a rock too but have a big fmic. I didnt get to drive the car long enough to play with it and watch temps. I was using 50/50 water/alcohol injection and I have the injection at the start of the greddy elbow and the AIT sensor right where the AWS would go if it was on the greddy elbow. what do you guys think of this? Do you think the water was just spraying right on the sensor and giving false low readings? Should I relocate it further away from the sensor in the intercooler pipe? I figure it will just make the car run richer because it will think the air is colder than it really is. I dunno this injection BS just sounds flakey to me. I do feel better or safer when I have it on though for some reason. my tank is 3/8 of a gallon and it takes about 2 weeks before I have to fill it up under moderate driving.

any comments?