IAT Sensor Placement with Meth Injection
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Joined: Sep 2007
Posts: 39
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From: Colorado
I have heard fears of getting the "wet bulb" effect, where the temperature reported by the IAT sensor is far lower than the actual IAT, resulting in over-aggressive timing. But a proper system will not have that issue unless the nozzle is essentially right next to the sensor to the point of having an obstructed spray pattern.
The other situation that occurs in some applications is an IAT sensor integrated into the MAF sensor. In that case spraying pre-IAT is a bad idea.
The other situation that occurs in some applications is an IAT sensor integrated into the MAF sensor. In that case spraying pre-IAT is a bad idea.
When the IAT is located after the meth injection nozzle the ECU will read a cooler inlet air charge and calculate a larger volume of air going into the engine then what is actually present. The ECU will respond to the cooler temp and add more fuel resulting in a richer mixture into the motor then needed.
Some tuners are aware of this and choose to locate the IAT after the meth nozzle. This is done as a safety factor in the tune to confirm meth injection is occurring. If the air charge is too hot, the tune is adjusted to pull timing. Fueling is adjusted in their tune to accommodate the artificial reading.
This is more common on the Mustangs that have two IATs one being located in the Hot Wire type of MAF sensor and one after the blower.
Some tuners are aware of this and choose to locate the IAT after the meth nozzle. This is done as a safety factor in the tune to confirm meth injection is occurring. If the air charge is too hot, the tune is adjusted to pull timing. Fueling is adjusted in their tune to accommodate the artificial reading.
This is more common on the Mustangs that have two IATs one being located in the Hot Wire type of MAF sensor and one after the blower.
Here is a quote from AEM Forums, specific to their AEM Meth kit.
http://forum.aempower.com/forum/inde...html#msg134423
Check your AIT after you spray your meth.
http://forum.aempower.com/forum/inde...html#msg134423
Check your AIT after you spray your meth.
Nutz, you bring up some very good points that highlight the general misunderstandings that many people have about water/methanol injection. First, when a liquid changes state and becomes a gas the change is endothermic meaning that energy is absorbed and in our case the energy is the heat in our air charge. So, as the atomized water/methanol vaporizes it absorbs heat from the air charge which in turn cools the air charge. In my years of testing and tuning water/methanol injection systems I've seen IAT reductions as large as 100 degrees F.
Now, following the Ideal Gas Law, which is further supported by Charles' Law and Boyles' Law, we know that when you cool a gas it condenses and its volume decreases for a constant mass so effectively, a gas will take up less space when it is cooled. Obviously our volume constraint is fixed (volume of intake manifold, intake ports, combustion chamber, etc, stays the same) so with a cooled and condensed air charge we are able to essentially increase the mass of air that will physically fit inside our engine. When you increase the mass of something while keeping its volume fixed you increase its density, not decrease.
The suggestion that water displaces oxygen to a point where the density of the air charge is decreased in this application is incorrect. It is generally understood that water vapor will in fact decrease the density of air IF and only IF there is no change in pressure or temperature. This is obviously not the case with water/methanol injection as the temperature is significantly decreased which thereby increases the density of the air charge which greatly offsets the potential displacement of air when introducing water vapor into the air charge.
This will be the one and only time I post this information. These points are unargueable and can be verified in any high school physics book. The merits of water/methanol injection have been well reviewed and documented by people like Sir Harry Ricardo and organizations like the Society of Automotive Engineers for decades. There are countless resources available if you should choose to further research this yourself.
Now, following the Ideal Gas Law, which is further supported by Charles' Law and Boyles' Law, we know that when you cool a gas it condenses and its volume decreases for a constant mass so effectively, a gas will take up less space when it is cooled. Obviously our volume constraint is fixed (volume of intake manifold, intake ports, combustion chamber, etc, stays the same) so with a cooled and condensed air charge we are able to essentially increase the mass of air that will physically fit inside our engine. When you increase the mass of something while keeping its volume fixed you increase its density, not decrease.
The suggestion that water displaces oxygen to a point where the density of the air charge is decreased in this application is incorrect. It is generally understood that water vapor will in fact decrease the density of air IF and only IF there is no change in pressure or temperature. This is obviously not the case with water/methanol injection as the temperature is significantly decreased which thereby increases the density of the air charge which greatly offsets the potential displacement of air when introducing water vapor into the air charge.
This will be the one and only time I post this information. These points are unargueable and can be verified in any high school physics book. The merits of water/methanol injection have been well reviewed and documented by people like Sir Harry Ricardo and organizations like the Society of Automotive Engineers for decades. There are countless resources available if you should choose to further research this yourself.
I have tested the life of a GM AIT sensor under a 50/50 water meth mixture. We insured that prior to getting to the sensor that the mix was near full evaporation.
Its $20 sensor so we wanted to see how long it would last. The sensor was put in the factory spot on the 2005 and up intake manifold. We got 6 weeks daily driving + full pulls out of the sensor with no funky AFR or readings but this is with a well set up HFS-6 system on speed density. I would recommend if running this setup you put the jets after the AIT. There is no guarantee 6 week life span, just what we observed. It will fail some sooner some later. Unless your direct port (which he is now) put the sensor downstream.
Thanks
Evan Smith
Its $20 sensor so we wanted to see how long it would last. The sensor was put in the factory spot on the 2005 and up intake manifold. We got 6 weeks daily driving + full pulls out of the sensor with no funky AFR or readings but this is with a well set up HFS-6 system on speed density. I would recommend if running this setup you put the jets after the AIT. There is no guarantee 6 week life span, just what we observed. It will fail some sooner some later. Unless your direct port (which he is now) put the sensor downstream.
Thanks
Evan Smith
I've had mine in that same spot, on the IM next to the factory MAP sensor for 13 months and 17,000 miles now with zero issues, I run 50/50 daily. I have an aquamist HFS-1 spraying two nozzels: 1.0 and .9, yielding about 900cc/min of meth/water being dumped past this sensor regularly. 
i have a question guys, i got a sensor and its a 3/8 NTP. I am going meth injection soon so planning on putting it just after the BOV tube. to get the cooling from 1 of the jets but not the 2nd jet.... the question i had was would it be ok to just tap the UCIP and put the sensor in or would it not hold and fall off and i would be better off welding a fittign to the UCIP and then screwing in the MAT sensor??
i have a question guys, i got a sensor and its a 3/8 NTP. I am going meth injection soon so planning on putting it just after the BOV tube. to get the cooling from 1 of the jets but not the 2nd jet.... the question i had was would it be ok to just tap the UCIP and put the sensor in or would it not hold and fall off and i would be better off welding a fittign to the UCIP and then screwing in the MAT sensor??
Not really enough fat in the intercooler pipe just to tap it. I normally either get someone to put a big blob of weld on the pipe and drill and tap through that or the better way is to weld a thicker piece of metal onto the pipe and drill and tap through that.
Well from what I was told by a tuner, the best place for the IAT sensor would be after the BOV in the UICP and before the Throttle body. The Meth nozzles after the IAT sensor. If you have an aluminum UICP you can order an Aluminum Bung and have a local welding shop weld it for you.
