IAT Relocate Mod!
tahts cool and all but the reason it was in the air lid was to measure the air after it was filtered. there are some quick temp chagnes and that will give false readings. that will give ambient temps not intake temps IMO. you have to account for ALL air taken in not just the air at the front of the box.
http://forum.efilive.com/showthread....ghlight=sensor
Did this on my last car. Definitely would recommend relocating the IAT sensor for any N/A LS1. Our lids get heatsoaked pretty bad. The IAT is meant to measure the outside air temp...not the air temp plus the heatsoaked lid. The charge temp blending table is there to compensate for any heatsoak picked up from air traveling through the intake tract into the cylinders. Inaccurate IATs hurt consistent fueling.
On top of all of this, I began to wonder (when I was experimenting with this) what other tables exist in the PCM (but are unseen in our software) that affect fueling based on IATs/ECTs. I know for a fact there are over 3,000 different calibrations in the PCM. Yet, we can see ~10% of them....
Did this on my last car. Definitely would recommend relocating the IAT sensor for any N/A LS1. Our lids get heatsoaked pretty bad. The IAT is meant to measure the outside air temp...not the air temp plus the heatsoaked lid. The charge temp blending table is there to compensate for any heatsoak picked up from air traveling through the intake tract into the cylinders. Inaccurate IATs hurt consistent fueling.
On top of all of this, I began to wonder (when I was experimenting with this) what other tables exist in the PCM (but are unseen in our software) that affect fueling based on IATs/ECTs. I know for a fact there are over 3,000 different calibrations in the PCM. Yet, we can see ~10% of them....
However, I still assume that we don't have full control over fueling. I'm not saying we don't have enough control to get the job done - just that I can't imagine the PCM's control over the secondary functions (i.e. non-fuel/air/spark related tables) make up the other 2700+ tables we can't see.
The thing is, the stock PCM is "massaging" the IAT and ECT
data to get to manifold air temp. No matter where you move
it this will still go on. Question is, given the downstream PCM
hoodoo, what is the quantity you really want to be feeding
it?
This is what I have not seen explained. Though Marcin
(redhardsupra) has been working on methods of tweaking the end
result, and I believe MAT may be coming as an available scanner
output (if it's not here already) for HPT.
Maybe somebody with a spare thermocouple could stuff one
down the manifold (EGR port, MAP grommet, unused nitrous boss,
etc.) and get a correlation between IAT (various schemes) ->
MAT (PID) and the logged thermocouple manifold temp. This
would let us all know what's what (for the given hardware at
least).
data to get to manifold air temp. No matter where you move
it this will still go on. Question is, given the downstream PCM
hoodoo, what is the quantity you really want to be feeding
it?
This is what I have not seen explained. Though Marcin
(redhardsupra) has been working on methods of tweaking the end
result, and I believe MAT may be coming as an available scanner
output (if it's not here already) for HPT.
Maybe somebody with a spare thermocouple could stuff one
down the manifold (EGR port, MAP grommet, unused nitrous boss,
etc.) and get a correlation between IAT (various schemes) ->
MAT (PID) and the logged thermocouple manifold temp. This
would let us all know what's what (for the given hardware at
least).
My only concern would be finding out that they match and the PCM's massaged number is only for internal use. IF the modified result isn't reported than we are back to square one!
The fact the PID was named SAE.IAT and not GM.IAT makes me want to hope what you say isn't true.
I'm with you on this one. Why in the hell did you move it? did you do cuz you got into mod fever and had to do something? You need to put that thing back man...otherwise good luck with running rich when its cold out; you just added a whole new tuning factor thats gonna cause you trouble
Some of us have our reasons...especially running an open loop SD tune like I do. I, too, have relocated my IAT sensor, and have had surprisingly good results, and is why it stays where it is...in a small, black box with limited airflow up by my driver's side headlight. Granted, I don't go purporting this as the end-all, be-all of IAT locations, but it works for me, and quite well at that regardless of ambient temps.
I've had the distinct pleasure of starting my car up on a nice, sunny, Florida summer day, and my IAT sensor (while still in the air lid) was reading 149* after being in the store for 10 minutes. Talk about fucked up fueling...
Since everyone's posting their take on things, i'll throw in my 2 cents...
we got two temp probes because we cant cram a probe inside of a cylinder (although Christian's pictures show you can put it much closer to 'the action' than most placements). with the two probes measuring the biggest source of heat (ECT) and the coldest airstream (IAT), out temperature is gonna be somewhere in between. with the bias/filter setup we can estimate the real temp fairly well. however, modding the intake system throws off the parameters of our estimation. thus, we must recalibrate the parameters to regain the precision of our estimation.
after looking at a lot of logs, here's my observations:
1. cold air intakes require the bias to shift more toward IAT, at any significant airflow
2. cutting a hole in your intake for more 'ram air' effect sucks up a lot of heat while idling, needing the bias to be more toward ECT at the idle airflow numbers
3. the filter value seems to depend on how far away that IAT sensor is from the intake. temp in the airbox changes very quickly, but the temp we care about, the one in the intake, doesn't change as quickly, so you need to 'slow down' the filter if you're putting it farther away from the intake.
all these are 'rule of thumb' observations to which of course i've seen exceptions, but than again, there's so many variables involved here it's hard to keep all the changes attributed to such a small subset of variables like the bias/filter tables.
and in case you havent seen my paper (shameless plug warning!), here's a link:
http://redhardsupra.blogspot.com/200...-modeling.html
we got two temp probes because we cant cram a probe inside of a cylinder (although Christian's pictures show you can put it much closer to 'the action' than most placements). with the two probes measuring the biggest source of heat (ECT) and the coldest airstream (IAT), out temperature is gonna be somewhere in between. with the bias/filter setup we can estimate the real temp fairly well. however, modding the intake system throws off the parameters of our estimation. thus, we must recalibrate the parameters to regain the precision of our estimation.
after looking at a lot of logs, here's my observations:
1. cold air intakes require the bias to shift more toward IAT, at any significant airflow
2. cutting a hole in your intake for more 'ram air' effect sucks up a lot of heat while idling, needing the bias to be more toward ECT at the idle airflow numbers
3. the filter value seems to depend on how far away that IAT sensor is from the intake. temp in the airbox changes very quickly, but the temp we care about, the one in the intake, doesn't change as quickly, so you need to 'slow down' the filter if you're putting it farther away from the intake.
all these are 'rule of thumb' observations to which of course i've seen exceptions, but than again, there's so many variables involved here it's hard to keep all the changes attributed to such a small subset of variables like the bias/filter tables.
and in case you havent seen my paper (shameless plug warning!), here's a link:
http://redhardsupra.blogspot.com/200...-modeling.html
Wow do I have a lot of reading to do. I never thought about how much the IAT would get biased sitting idle, but then again, isn't the air getting heated up resulting in higher inlet temperatures?
What about going to the MAF's with the intigrated AIT in them, the 85mm maf's? Is that a better option? I recently went with a FAST 90/90 setup and am looking to either ditch the maf all together, or go with a larger one. If running the larger maf with intigrated temp sensor is the way to go, then that will be the best path for me.
Thanks.
What about going to the MAF's with the intigrated AIT in them, the 85mm maf's? Is that a better option? I recently went with a FAST 90/90 setup and am looking to either ditch the maf all together, or go with a larger one. If running the larger maf with intigrated temp sensor is the way to go, then that will be the best path for me.
Thanks.
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why move it? because the heat soaked stock location gives bad fueling in OLSD under certain conditions, especially on the GTO. as has been noted the PCM does calculations based off of ECT and IAT. by adjust the bias and filtering under different air flows the ECM can make fairly accurate calculations of cylinder air temps based off of the two extremes of ambient air entering the stream and engine coolant temps. a heat soaked sensor fakes out the calculations until it cools off.
I don't like the MAF/IAT combo setup because I believe the MAF is part of the problem. The MAF suffers from heatsoak just the same (if not more) as the lid does where the IAT is located - especially if the MAF has a metal housing.
I moved my IAT on my last N/A setup to just in front of the lid (behind the washer fluid tank). The only thing within a few inches of the IAT was the zip tie I used to hold it in place. So, it was exposed....but, it was in a position that didn't get wet when driving in the rain. It measured underhood temps more accurately when sitting in traffic (10~20* above ambient) and would drop to ~5* within ambient temps once I started moving. Again, totally worth doing...and I'd do it again if I go back to N/A.
I moved my IAT on my last N/A setup to just in front of the lid (behind the washer fluid tank). The only thing within a few inches of the IAT was the zip tie I used to hold it in place. So, it was exposed....but, it was in a position that didn't get wet when driving in the rain. It measured underhood temps more accurately when sitting in traffic (10~20* above ambient) and would drop to ~5* within ambient temps once I started moving. Again, totally worth doing...and I'd do it again if I go back to N/A.
I don't like the MAF/IAT combo setup because I believe the MAF is part of the problem. The MAF suffers from heatsoak just the same (if not more) as the lid does where the IAT is located - especially if the MAF has a metal housing.
I moved my IAT on my last N/A setup to just in front of the lid (behind the washer fluid tank). The only thing within a few inches of the IAT was the zip tie I used to hold it in place. So, it was exposed....but, it was in a position that didn't get wet when driving in the rain. It measured underhood temps more accurately when sitting in traffic (10~20* above ambient) and would drop to ~5* within ambient temps once I started moving. Again, totally worth doing...and I'd do it again if I go back to N/A.
I moved my IAT on my last N/A setup to just in front of the lid (behind the washer fluid tank). The only thing within a few inches of the IAT was the zip tie I used to hold it in place. So, it was exposed....but, it was in a position that didn't get wet when driving in the rain. It measured underhood temps more accurately when sitting in traffic (10~20* above ambient) and would drop to ~5* within ambient temps once I started moving. Again, totally worth doing...and I'd do it again if I go back to N/A.
I still stuck a 85mm MAF on my car cause it is lighter. I kept a discrete IAT sensor stuck in front of the lid by the rad support.
And isn't that what you want? I think so. The factory probably just stuck it there because it was easier and the MAF is immune to heatsoak because the elements are powered and abouve ambient temps. The IAT inside the MAF would still be prone to heatsoak though.
I still stuck a 85mm MAF on my car cause it is lighter. I kept a discrete IAT sensor stuck in front of the lid by the rad support.
I still stuck a 85mm MAF on my car cause it is lighter. I kept a discrete IAT sensor stuck in front of the lid by the rad support.
Would this work? (on someone else's motor, of course) Take out a sparkplug and replace it with a temp sensor (obviously disconnecting the corresponding injector). Log the difference between the air temp measured at the IAT and in the cylinder at as many different conditions as possible. Then use the corresponding data to tweak the IAT vs ECT blending to match the actual measured results. Of course explaining to everyone why you have all sorts of sensors hooked to your motor and it still skips might get tiring.
Would this work? (on someone else's motor, of course) Take out a sparkplug and replace it with a temp sensor (obviously disconnecting the corresponding injector). Log the difference between the air temp measured at the IAT and in the cylinder at as many different conditions as possible. Then use the corresponding data to tweak the IAT vs ECT blending to match the actual measured results. Of course explaining to everyone why you have all sorts of sensors hooked to your motor and it still skips might get tiring.
Sounds like something that you would have to have made.
i seriously doubt that would work. the temps would change insanely quickly, due to air coming in/out, and getting compressed and uncompressed hundreds of times a second. do you know a temp probe that could register all these changes precisely, and quickly enough? i sure dont...
i think the system GM came up with is fine, we just gotta master calibrating it.
i think the system GM came up with is fine, we just gotta master calibrating it.
Would this work? (on someone else's motor, of course) Take out a sparkplug and replace it with a temp sensor (obviously disconnecting the corresponding injector). Log the difference between the air temp measured at the IAT and in the cylinder at as many different conditions as possible. Then use the corresponding data to tweak the IAT vs ECT blending to match the actual measured results. Of course explaining to everyone why you have all sorts of sensors hooked to your motor and it still skips might get tiring.
GM's setup is ok, I just think coming up with a way to actually measure would be an interesting engineering theory exercise. I wonder how precisely high speed thermal image photos could be measured?
I don't think you care about in-cylinder temps. You care about
the air mass just before the fuel is shot. I'd say this is your nitrous
boss on the intake (or a similarly located hole).
If we get to see manifold absolute temp (as-calculated) and the
real temp then this is enough to bed in the charge bias table
and criticize various IAT locations.
the air mass just before the fuel is shot. I'd say this is your nitrous
boss on the intake (or a similarly located hole).
If we get to see manifold absolute temp (as-calculated) and the
real temp then this is enough to bed in the charge bias table
and criticize various IAT locations.
Does the charge temperature blending only work in a MAF tune? Or does it work in a OL SD tune as well? Redhardsupra, what is the procedure you would go through to dial in your filters? I read your paper that you wrote, but it didn't go into much depth on how you would go about it. And, how exactly is your tempmodeling spreadsheet supposed to work? What do the abbreviations mean?
Thanks,
Adrian
Thanks,
Adrian
