IAT Sensor - Where is yours?
10-27-2011, 01:34 PM
#11
Thread Starter
I don't want to experiment, I want to go with what works. If Honda did it in 2006, I don't see enough downsides to not go that route (my previous points notwithstanding)
10-27-2011, 01:44 PM
#12
How do you know what works if you don't experiment
Or let some else 'experiment' and get back to you regarding the GM sensor - what's the response rate of the two, id be surprised if someone actually logged the two IAT's.All i know is i experimented and made a difference, I'm not arguing why honda moved it - its logical why they did.
I doubt the IAT sensor has a slow response, but I'm intrigued how important is the response time is since there's only some much heat that can dissipate in a given time.
10-27-2011, 01:56 PM
#14
Registered User
Mine is in the charge piping about 6 inches before the TB..no heat soaking problems. I cant see there being much of a significant temperature increase at all between where my sensor is and the air reaching the cylinders considering the air is flowing at over 210 litres per second at 9000rpm @ 10psi.
Dan
Dan
10-27-2011, 01:59 PM
#15
10-27-2011, 02:01 PM
#16
Mine is in the charge piping about 6 inches before the TB..no heat soaking problems. I cant see there being much of a significant temperature increase at all between where my sensor is and the air reaching the cylinders considering the air is flowing at over 210 litres per second at 9000rpm @ 10psi.
Dan
Dan
'in WOT'.
10-27-2011, 02:52 PM
#17
Thread Starter
Not an attack at you, just saying in general.
02-15-2012, 11:18 AM
#18
Thread Starter
Still haven't gotten around to moving my IAT sensor, but plan to soon. Ran across this old post on H-T. Helps explain why the move is good idea for FI applications
Originally Posted by blundar
My "theory" is mostly based on experience, and partly on theory.
Experience is fairly straightforward - I've been able to control AFR fluctuations as a result of weather significantly better with the IAT in a charge pipe. The end.
Theory:
Modified Speed density system.
PV=nRT ideal gas law, n (moles or air) = P (pressure - MAP sensor) * V (volume - RPM/2 * displacement)/ R(Ideal gas constant) * T (temperature - IAT, ECT sensors)
The purpose of IAT and ECT corrections is termed "density correction." Temperature affects the density of a gas, density affects how many moles of gas are present. This is critical information if you are supplying fuel in proportion to the number of moles of gas present. DENSITY CORRECTION IS NEVER PERFECT. ECT and IAT sensors provide a means for an EMS to ESTIMATE charge temps. DENSITY plays a significant role in determining how much heat is picked up by air moving by. Denser air (as a rule of thumb) suffers less of a temperature change compared to less dense air. (ever wonder why P72-derived EMSes have MULTIPLE IAT correction tables for different loads?) You cannot measure the instantaneous temperature of gas as it enters the combustion chamber - this is what matters for the ideal gas law.
With the IAT in the intake manifold, even the plastic sensor will tend to drift to the same temperature as the intake manifold. Sometimes, this is very accurate. Sometimes, this is a horrible ESTIMATION.
Ever wonder why the ECT adjustment is present full-time? What temperature is the cylinder head? (hopefully) What gets pumped through the head continuously? Coolant, perhaps? ECT adjustment is active to account for the density changes that result from the intake charge absorbing heat from the head. If you move the IAT to the charge pipe, your ECT correction takes over the role of account for temperature change in both the head and the intake manifold.
With the IAT in the charge pipe, there are several things at work:
-Negligible heatsoaking of charge pipe compared to intake manifold means the sensor reads closer to actual air temperatures in the charge pipe
-Placement in charge pipe generally improves transient response time.
-The amount of heat transfer that happens in the charge pipes versus the amount of heat transfer in the intake manifold and head is relatively small. This means that with the IAT in the charge pipes, the temperature of the gas prior to entering the IM + head, where most heat transfer happens, is known much more precisely.
-Correction wise, IAT correction is solely responsible for accounting for density changes as a result of charge air temps - changes from heat absorbtion in intake manifold and head are accounted for with ECT.
-Net result: n=PV/RT gets a more accurate estimation of T from the more accurate measurement of charge temps prior to the intake manifold combined with the additional correction provided by ECT correction modelling changes.
"If your tuner knows how to work density correction tables." comment basically means understanding what the ECU is doing and why enough to make a semi-intelligent decision about how muc IAT and how much ECT correction to use. You can actually do a pretty damn good job accounting for the heatsoaking effects of heads and intake manifolds by varying the amount of ECT vs. IAT correction, but again load/density affects things a lot...
The BEST scheme would be to have multiple IAT sensors in order to be able to come up with a more accurate charge temp estimation, but that isn't often all that practical.
Autronic has a charge temp estimation table that can be just as large as the main VE/fuel tables. AEM's temperature correction leaves a lot to be desired - last time I checked, I didn't see much in the way of load-specific charge temp estimation control. The Honda engineers really tried hard back in the early 90s, that's all I have to say.
Hope that helps.
Experience is fairly straightforward - I've been able to control AFR fluctuations as a result of weather significantly better with the IAT in a charge pipe. The end.
Theory:
Modified Speed density system.
PV=nRT ideal gas law, n (moles or air) = P (pressure - MAP sensor) * V (volume - RPM/2 * displacement)/ R(Ideal gas constant) * T (temperature - IAT, ECT sensors)
The purpose of IAT and ECT corrections is termed "density correction." Temperature affects the density of a gas, density affects how many moles of gas are present. This is critical information if you are supplying fuel in proportion to the number of moles of gas present. DENSITY CORRECTION IS NEVER PERFECT. ECT and IAT sensors provide a means for an EMS to ESTIMATE charge temps. DENSITY plays a significant role in determining how much heat is picked up by air moving by. Denser air (as a rule of thumb) suffers less of a temperature change compared to less dense air. (ever wonder why P72-derived EMSes have MULTIPLE IAT correction tables for different loads?) You cannot measure the instantaneous temperature of gas as it enters the combustion chamber - this is what matters for the ideal gas law.
With the IAT in the intake manifold, even the plastic sensor will tend to drift to the same temperature as the intake manifold. Sometimes, this is very accurate. Sometimes, this is a horrible ESTIMATION.
Ever wonder why the ECT adjustment is present full-time? What temperature is the cylinder head? (hopefully) What gets pumped through the head continuously? Coolant, perhaps? ECT adjustment is active to account for the density changes that result from the intake charge absorbing heat from the head. If you move the IAT to the charge pipe, your ECT correction takes over the role of account for temperature change in both the head and the intake manifold.
With the IAT in the charge pipe, there are several things at work:
-Negligible heatsoaking of charge pipe compared to intake manifold means the sensor reads closer to actual air temperatures in the charge pipe
-Placement in charge pipe generally improves transient response time.
-The amount of heat transfer that happens in the charge pipes versus the amount of heat transfer in the intake manifold and head is relatively small. This means that with the IAT in the charge pipes, the temperature of the gas prior to entering the IM + head, where most heat transfer happens, is known much more precisely.
-Correction wise, IAT correction is solely responsible for accounting for density changes as a result of charge air temps - changes from heat absorbtion in intake manifold and head are accounted for with ECT.
-Net result: n=PV/RT gets a more accurate estimation of T from the more accurate measurement of charge temps prior to the intake manifold combined with the additional correction provided by ECT correction modelling changes.
"If your tuner knows how to work density correction tables." comment basically means understanding what the ECU is doing and why enough to make a semi-intelligent decision about how muc IAT and how much ECT correction to use. You can actually do a pretty damn good job accounting for the heatsoaking effects of heads and intake manifolds by varying the amount of ECT vs. IAT correction, but again load/density affects things a lot...
The BEST scheme would be to have multiple IAT sensors in order to be able to come up with a more accurate charge temp estimation, but that isn't often all that practical.
Autronic has a charge temp estimation table that can be just as large as the main VE/fuel tables. AEM's temperature correction leaves a lot to be desired - last time I checked, I didn't see much in the way of load-specific charge temp estimation control. The Honda engineers really tried hard back in the early 90s, that's all I have to say.
Hope that helps.
02-15-2012, 12:22 PM
#19
Good info i was thinking about moving mine and making a blanking plate. But because i use a greddy emanage ultimate and thus the stock ECU is kinda in the loop it might not be a good idea, as i dont have any correction tables to alter???I have witnessed on a airfield taster day the IAT sensor reach temperatures of 149F!! there was a lot of waiting around (15 cars +), still its bloody hot. In WOT it will pull a hell of a lot timing.
02-15-2012, 12:41 PM
#20
Thread Starter
Good info i was thinking about moving mine and making a blanking plate. But because i use a greddy emanage ultimate and thus the stock ECU is kinda in the loop it might not be a good idea, as i dont have any correction tables to alter???I have witnessed on a airfield taster day the IAT sensor reach temperatures of 149F!! there was a lot of waiting around (15 cars +), still its bloody hot. In WOT it will pull a hell of a lot timing.