-= Ultimate Emanage Tuning Thread =-

[lethal_vr4]

Originally Posted by badass3000

you will be fine as long as the sensor is near your air filter, like taped to it.
There is no reason to put it in the manifold.

Are you suggesting he put the IAT before the turbos? I put mine mid y-pipe.

[badass3000]

Yes.
the temp sensor is going directly to the stock ECU so it should measure the same air as the MAS did, not post turbo/intercooler/meth inj/ ect.
Only thing thats going to happen by measuring post turbo is the air should be hotter and make the ECU goto a more conserative timing map. IE lose power.

[lethal_vr4]

All the speed density conversions I've seen place the IAT POST turbo.

[Racer_X]

it actually is a better idea to put the IAT sensor pre turbo for the reasons badass gave. Plus, when you put the sensor post turbo, it becomes "very" hard to tune it independent of boost. as boost pressures and efficiencies change, the charge air temp changes a good bit. these temp changes are usually consistently dependent on outside air temp and boost level. You are already tuning "per boost" with the map sensor, so it becomes really hard to define how much richer or leaner the car should be based on your boost map with temperature. With the sensor before the turbo, the temperature will stay consistent with variable boost, and will only change when the inlet air temp changes (which makes big variable swings in charge temps because of compressor efficiency). These swings should be "solely" temperature dependent and you can tune for them (making the IAT sensor a useful tuning and A/F adjustment tool). I would honestly recommend using a steady state resistor for what the ecu sees and just tuning per the IAT sensor through the e-manage with your own pre-made circuit (not hard to make). That will keep you from getting wonky fuel and timing bugs to work out, and you can basically tune clean. This is how I am setting up my car.

[disturbedkorn]

I prefer using two air temperature sensors with EMU. I use the stock sensor to feed the stock ecu the temperature entering the air filter. You can dig it out of the stock MAF and mount it somewhere near or in the air filter. Then I use the GM IAT in the piping directly before the throttle body to measure the temperature of the air entering the motor. Air temperature is an important compenent in figuring the air for a speed density setup. The EMU uses the calculated speed density and then converts or translates that to a karman vortex frequency that our stock ecu can use. In some cases you can have cold intake air and hot post turbo temps. Other times both can be cold or both can be hot. It can and will vary enough to matter especially with turbos being run outside their optimum efficiency and/or inadequate intercooling. You will be constantly adjusting the tune (or running crappy) unless you have the ability to monitor both.

[badass3000]

although that is a great idea, I dont here Trevor using a "Hot" IAT. and he pretty much started using the Ultimate (MAPECU) b/c he hated having to have to retune due to temp changes.

[Gray Haze]

I always put em in a filter, or the filtered area. Never in the manifold/IC Pipe unless its an AEM.

And when the ECU sees High IAT, it advances timing, when it sees cold IAT, it reduces timing due to air density.

[disturbedkorn]

The temperature pre turbo can be much lower than the temperature post turbo as I'm sure you know. To accurately add fuel in all occasions you need to know the true mass of air entering the motor.

The ideal gas law is P x V = n x R x T
P = pressure
V = volume
n = number of moles
R = gas constant
T = temperature

Density in this case is the number of molecules in a certain volume. The molar volume can be expressed as D = n / V
D = density
n = number of molecules
V = volume

Combine the two and Density becomes D = P / (R x T)
D = density, kg/m3
P = pressure, Pascals
R = gas constant, J/(kg x degK) 287 for dry air
T = temperature, degK

So running the numbers I get the following densities at 15C (60F) and 65C (150F):

101325p, 15 degC = 1.225 kg/m3
101325p, 65 degC = 1.044 kg/m3

So if the sensor at the intake read 15 degC and the air temperature entering the motor was 65 degC, the density would be around 17% too high.

At twice the atmosphere you get the same result:

202650p, 15 degC = 2.450 kg/m3
202650p, 65 degC = 2.088 kg/m3

17% high

Now if the EMU is not using the IAT and is only monitoring it for datalogs, than you'd want to have just the one in the filter. Furthermore, if the EMU is not using it for speed density conversion than that's retarded since the temp of the air is such a vital component in figuring the amount of molecules entering the engine.

Disclaimer: I'm not an engineer. But I've studied some thermo dynamics and fluid dynamics in order to understand cars which are my passion.

[Racer_X]

Well, the nature of karman vortex air flow meters is to measure based on the velocity of the air going through the meter. That is why the stock meter also has an intake air temperature sensor. The velocity of air flow through the calibrated meter is calculated to be a certain CFM value based on a normalized temperature, and the mass of the air is calculated by adjusting that normalized value for temperature with the actual IAT. THe ecu does this by injector duty cycle percentage. That is why it is really hard to keep the same tune on a really cold night vs. a really hot day if you have bigger injectors. The ecu is adding or subtracting fuel to try to calibrate for the air density change based on a downstream adjustment (downstream of the normal logic flow). Kind of like an afterthought. The EMU does create a karman vortex frequency based on MAP and RPM, and IAT is simply an option. This is exactly how the OEM system does it (although it is more accurate). You can get very close by saying air flow through x cross sectional area will be predictable given the engine RPM and manifold pressure, assuming intake IAT is constant. The "density" may change with temp, but the velocity will be the same.

Now, if you hold the temp the ecu sees as constant (with a resistor) then the ecu no longer is able to make the downstream injector percentage adjustment to compensate for air density changes, and you "have" to make that change with the EMU if you want the tune to stay the same at differnet inlet temperatures. This can be done much more accurately adjusting from scratch with the IAT fuel adjustment in the emu as opposed to doing the adjustment on top of the ecu's adjustment. Also, vehicle speed and intercooler flow surface area has a good bit to do with the density adjustment as well. This is because the charge temp is different at 100 mph at 15 psi at 6k RPM with 65 degree ambient temp than it is at 15 mph. That's why the EMU has vehicle speed based fuel adjustments as well. OF course, if you put the IAT in the manifold, you wouldn't need vehicle speed adjustments, but you would also need a way to produce an entire base fuel map at a static temperature.............................................not going to happen without an engine dyno.

To get a really basic tune, just use the map sensor. Trying to adjust the fuel trim using the IAT after the turbo brings in way to many variables to be worthwile. How do you know exactly "how much" to adjust when you have 100 degree temp swings in a single pull???????? Sure you can guess, but your guess is going to affect your entire map in a bad way and then you are trying to adjust one value with 2 variables. Doesn't work well.

If you put the IAT in the turbo inlet pipe, or near the filter, you can get a much better calibration, but it still won't be perfect. After you adjust for vehicle speed, then you will have a much better reading. That is assuming that the ecu isn't doing that as well..........that I am not sure of.

Irregardless of who is running what on whatever or why, this is how it works.

[disturbedkorn]

Well, that makes perfect sense now. I find I'm always learning something with these ECUs. Thanks Racer X.