Air charge Temp Sensor

[TurboDave]

TurboDave , have any real tests been done to confirm any difference in performance based on IAT sensor placement ? I am using IAT sensor in stock location and I wonder why does it matter since I use MAFPRO for partial and WOT AFR tracking with wide band , would it not AFR be adjusted no matter what inputs say to your target AFR ? is it NOT the whole idea ? by the way I switched to speed density without IAT compensation mode for a while to see what happens and I did not see any difference , is it because the tracking works so good or is it me doing something wrong ?

Well, I don't run a wideband yet, so I can't yet address that issue. But I do monitor the signal "density compensation" on my laptop or MafPro and I do notice that the air temp going into the engine does in fact add or subtract fuel based on the temp, or at least it says it is. It isn't a lot, unless the temps are quite cold or quite warm. I think the switch point for it is somewhere in the mid 70°'s as I recall.
Don't know about your last question. Your tune might be extremely close and not a lot of tracking changes needed. Keep in mind we're only talking a few % either way so you may not have any issues.

 

[VadersV6]

Ive always wondered why they would bother with an IAT sensor, if they arent going to use is for density compensation. Alot of other EFI cars use this sensor for this purpose. When the motor gets heat soaked, the incoming air is really hot, and the computer pulls alot of timing and makes a huge difference in power. Adding a 47k resistor inline with my IAT wires on my cobra made a massive difference in power after warmup (10hp, 10lbs tq peak to peak gain and 25 lbs in the midrange...and part throttle power difference and tip-in response was incredible) Basically, on the cobra, it restored all the timing retard related to heat soak. It also added timing if you went high enough on the resistance. I used a different thermistor on the GN....dont remember the value, but I got it to where the computer saw it as a 20 degree incoming air charge. I didnt really notice any difference in power but it did seem to be drinking alot more fuel. I didnt keep it on there long enough to notice anything for sure.

 

[HighPSI]

What's the max temp indication range for the stock IAT sensor?? I know the stock sensor just indicates "hot" on Scanmaster at 145'ish and higher. And, I'm sure that pressurized (and even intercooled) air in the up pipe would be in excess of 145!?

I have seen the sensor pegged at 255 on non-intercooled cars. I strongly recommend the slower reacting brass sensor for those applications. A couple of cars I have tuned have melted the Buick style open element sensor.

 

[TurboDave]

I have seen the sensor pegged at 255 on non-intercooled cars. I strongly recommend the slower reacting brass sensor for those applications. A couple of cars I have tuned have melted the Buick style open element sensor.

Which brings up a good point to ponder. The Buick sensor has the thermistor covered by a little "flimsy" plastic cage.
This would worry me running it down stream of the the alky nozzles because of the huge temerature swings. That would have to cause a lot of stress on the plactic parts, with possible downstream disintegration.

 

[VadersV6]

Which brings up a good point to ponder. The Buick sensor has the thermistor covered by a little "flimsy" plastic cage.
This would worry me running it down stream of the the alky nozzles because of the huge temerature swings. That would have to cause a lot of stress on the plactic parts, with possible downstream disintegration.

Theres nothing special about thermistors. Its really easy to make your own by just drilling out a factory sensor in a lathe...doesnt matter which...a coolant sensor, IAT sensor, etc. You just need the body and the plug. Just drill it out (a blind hole...leave the internal leads intact), order the right thermistor from digi-key, (whats the TR thermistor? 4.5k?...dont recall) solder it to the connector leads inside, and fill it with potting epoxy. Not that hard at all. I made my own for the cobra about 4 years back. It used a 10k ohm thermistor though. You dont need to worry about wattage ratings or anything. They have many styles to choose from at digi-key (online)...almost endless electronic component selection...You can make your own robust IAT sensor in 30 minutes. I actually made my own 2 years ago for the GN...just remembered. All it takes is the thermistor and a 1/4" NPT brass fitting. Mount it, fill it with potting epoxy and leave the leads sticking out, and tap it whatever way you prefer. Digi-Key also has an endless selection of connectors and plugs as well.

 

[TurboDave]

Theres nothing special about thermistors. Its really easy to make your own by just drilling out a factory sensor in a lathe...doesnt matter which...a coolant sensor, IAT sensor, etc. You just need the body and the plug. Just drill it out (a blind hole...leave the internal leads intact), order the right thermistor from digi-key, (whats the TR thermistor? 4.5k?...dont recall) solder it to the connector leads inside, and fill it with potting epoxy. Not that hard at all. I made my own for the cobra about 4 years back. It used a 10k ohm thermistor though. You dont need to worry about wattage ratings or anything. They have many styles to choose from at digi-key (online)...almost endless electronic component selection...You can make your own robust IAT sensor in 30 minutes. I actually made my own 2 years ago for the GN...just remembered. All it takes is the thermistor and a 1/4" NPT brass fitting. Mount it, fill it with potting epoxy and leave the leads sticking out, and tap it whatever way you prefer. Digi-Key also has an endless selection of connectors and plugs as well.

Sounds good and all, but for the average T/R guy like me, there are a huge number of us that don't have a lathe sitting around or have ready access to one.
Fabricators always make these types of things sound easy, but you must realize that 9 out of 10 of us aren't (fabricators, that is).
Sorta like the threads that followed the chinese headers around in the beginning. There were a few fabricator/welders that bought them, and made it sound Oh so simple to fix the multitude of mistakes on them, but they always forget, they (fabricators/welders) are in the extreme minority, and we can't all "just do it".

Hey, I have a novel idea, why don't you start a business building these "robust" sensors for those of us in the masses? Sounds like a good idea to me.

 

[Jerryl]

I have seen the sensor pegged at 255 on non-intercooled cars. I strongly recommend the slower reacting brass sensor for those applications. A couple of cars I have tuned have melted the Buick style open element sensor.

Cal,
This has always been a concern of mine.
Between heat, vibration, and the force of the air blowing across is .... it could be a disastrous experience. Thanks for the verification.

Is this the one you are referring to?
I just ordered one this weekend from FT last weekend.

 

[VadersV6]

Yeah I could make alot of them, but I dont really see whats so bad about the factory one.
If you wanted something really solid, I would drill a hole in the rear of the plenum lid, maybe 1/16NPT...really small and tap in there. Like I said before, if the thermistor is isolated from the body of the sensor, then there are no heat transfer issues. I can come up with something nice, but only if someone is going to buy it.
Who's willing to snip off the factory IAT connector? A different connector would have to be spliced on (1 minute job) and then the wires could be run to the rear of the plenum, or wherever people would want. I personally think the upper, center, rear (back wall toward the firewall) of the plenum lid is the perfect location for picking up the true temps with vaporized alky and all.

 

[VadersV6]

Hey, I have a novel idea, why don't you start a business building these "robust" sensors for those of us in the masses? Sounds like a good idea to me.

I have a couple ideas, (just for a few to make for guys on the board here).....different ways of terminating and housing the thermistor, but for the few here who may want a solid IAT sensor, how would you guys want to mount them? Using the thread of the stock sensor to screw it in the intake tube, or drilling and tapping the plenum lid and mounting there? With either idea, I'm looking at a 3/8" fine thread...normal threading, not tapered pipe threads....