What is the IAT Sensors job in SD Tune
01-23-2015, 02:57 PM
#6
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Gas law calculation of air mass includes absolute temp
as a prime factor (PV=nRT, or n=PV/(RT), meaning mole
mass goes as 1/(IAT+273) in celsius units.
The IAT used in the air mass calcs goes through the
"charge bias" whoop-de-do, blending ECT in more at
low gas flows where you have time to move the air
toward the wall temp (never mind that the composite
intake manifold bears hardly any relation to ECT temp,
only the head intake pocket).
Anyway, you can expect to see the same tune, same
BARO, same MAP & RPM deliver a different air mass
(calculation, and reality) on days with different tempertures.
Add to this that the IAT reading diverges, static and
especially on transient airflow changes, from the real
in-taken air temps by any engine bay duct and sensor
element heating, and you might just start to like the MAF
again.
as a prime factor (PV=nRT, or n=PV/(RT), meaning mole
mass goes as 1/(IAT+273) in celsius units.
The IAT used in the air mass calcs goes through the
"charge bias" whoop-de-do, blending ECT in more at
low gas flows where you have time to move the air
toward the wall temp (never mind that the composite
intake manifold bears hardly any relation to ECT temp,
only the head intake pocket).
Anyway, you can expect to see the same tune, same
BARO, same MAP & RPM deliver a different air mass
(calculation, and reality) on days with different tempertures.
Add to this that the IAT reading diverges, static and
especially on transient airflow changes, from the real
in-taken air temps by any engine bay duct and sensor
element heating, and you might just start to like the MAF
again.
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01-27-2015, 06:44 PM
#9
Not nesarly. You'll have to look at your log at commanded afr and compare it to your tune to see if they match. They could be commanding 12.1 afr, if your fuel table is off commanded will not equal real world. They could have 28 deg in the tune and a modifier is pulling it back to 25.
01-27-2015, 07:28 PM
#10
if properly calibrated wideband then that's where your at if logs that is just whats being commanded and likely is not a close representation of your actual afr...
the modifier tables lsx tuning is referring to would be the tables such as iat ,ect (coolant temp) ,etc... been a while since I have done any tuning but there are many tables that get referenced and can change things like timing and fueling depending on what data populates those tables , if zeroed out then they have no effect , zeroing out basically takes that variable away not saying right or wrong just stating how it works , typically any table that is a modifier can be set up to compensate for variables you may be chasing or may be the variable that has you chasing your tail if your not aware that data in the modifier tables is the reason your seeing variations....
01-28-2015, 08:28 AM
#12
Did you adjust the voltage offset to make your WB match in HPT and what it is in real world. 99% of the time I have tuned something remotely or through email and they were logging WB through the egr their WB was never reading right in the log according to the WB gauge in the vehicle.
01-29-2015, 07:52 PM
#14
Moderator
As JimmyBlue tried to explain, knowing the IAT is critical to proper operation. It is the (gas) LAW! On a hot day, the TPS will say its at 100%, the MAP will say its at 100kpa, but the air/oxygen density will be low, causing you to run richer than needed. Or, if you tune it perfectly on a hot day, then on a cold day you will run at WOT.
IIRC the difference is about 1% per 10F.
I also have a Victor Jr 4150 EFI manifold. Finding a place where the IAT doesn't get heat soak is difficult. I finally put it just behind the passenger side head light where it reads close to ambient air temperature; I have a raised hood with cowl induction and am therefore ingesting ambient temperature air.
IIRC the difference is about 1% per 10F.
I also have a Victor Jr 4150 EFI manifold. Finding a place where the IAT doesn't get heat soak is difficult. I finally put it just behind the passenger side head light where it reads close to ambient air temperature; I have a raised hood with cowl induction and am therefore ingesting ambient temperature air.
01-30-2015, 08:44 AM
#16
Moderator
Yes it is well documented on the HPT forum; IIRC I've seen a .doc or .pdf file on it. Since I run two AEM Widebands, one for each bank, I run direct connections through an additional connector near by OBD2.
01-30-2015, 02:12 PM
#17
I thought the IAT issue was more at idle in traffic where heatsoak is a real issue with messing with ambient temps. I have mine (as part of the slotted LS3 MAF) in the TSP 100mm MAF. I don't use the MAF, but I use the IAT there.
It gets heatsoaked at idle sitting around. But it's very close to ambient moving down the road.
It gets heatsoaked at idle sitting around. But it's very close to ambient moving down the road.
01-30-2015, 03:57 PM
#18
Moderator
When I had my IAT anywhere in the actual intake air stream, it would heatsoak to 140F while staging at the track and drop to 90F by the end of the run. So my A/F would change by 5%.
The factory is very good at keeping heatsoak to a minimum. My friend with a C5 says his IAT is only 10F over ambient when staging at the track. It is located in front of the radiator. In other words factory locations are pretty good, but custom locations can be a problem.
The factory is very good at keeping heatsoak to a minimum. My friend with a C5 says his IAT is only 10F over ambient when staging at the track. It is located in front of the radiator. In other words factory locations are pretty good, but custom locations can be a problem.
01-31-2015, 09:06 AM
#20
There are tons on factors in how heat soaked your IAT can get, IAT location, hood type, etc...with my extended sunoco hood against my windshield and IAT in front of my TB my IAT's would sky rocket because there wasn't anywhere for hot air to go.