could a rapid IAT reading cause a problem? plan on using TWO IAT sensor
09-30-2015, 04:34 AM
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could a rapid IAT reading cause a problem? plan on using TWO IAT sensor Im having some serious IAT heat soak since its currently placed where the EGR pipe used to be on ls1 intake. (right after the tb)
its picking up around 100*+ on stop and go and I know its not that hot up stream. The reason its there is because im using methanol 50/50 and wanted an accurate IAT reading. which works great under high speed or WOT. But it gets heatsoak and the car starts to idle bad and affects the drivability a bit.
About 3 feet up stream(intercooler pipe) behind the driver headlight i had originally put the iat sensor there to prevent heatsoak. it seems to work way better there but due to methanol i had to move it back.
Im thinking the best solution is run two IAT. 1 in the intake and one by the headlight. run a relay that is activated by my methanol kit. and under normal driving it sees the front(real temp) IAT but under WOT it energize the relay and now it will be using the one in the intake.
I think it would work, but will the PCM detect a problem because it is seeing 70-80* then a sudden jump to 100*(intake) before it gets cooled down by the methanol?
or will the pcm just compensate quickly and adjust?
what do you guys think?
its picking up around 100*+ on stop and go and I know its not that hot up stream. The reason its there is because im using methanol 50/50 and wanted an accurate IAT reading. which works great under high speed or WOT. But it gets heatsoak and the car starts to idle bad and affects the drivability a bit.
About 3 feet up stream(intercooler pipe) behind the driver headlight i had originally put the iat sensor there to prevent heatsoak. it seems to work way better there but due to methanol i had to move it back.
Im thinking the best solution is run two IAT. 1 in the intake and one by the headlight. run a relay that is activated by my methanol kit. and under normal driving it sees the front(real temp) IAT but under WOT it energize the relay and now it will be using the one in the intake.
I think it would work, but will the PCM detect a problem because it is seeing 70-80* then a sudden jump to 100*(intake) before it gets cooled down by the methanol?
or will the pcm just compensate quickly and adjust?
what do you guys think?
10-05-2015, 10:21 PM
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Well, I only have some experience with a NA car or two,
but I've never seen anyone say just where in a boosted
lineup, the IAT ought to be - what it ought to measure.
I imagine that trying to use IAT in the air after the
impeller is a bad idea, because IAT is slow and would be
impossible to rely upon outside steady-state, while speed
density (where IAT matters big time) is where you go in
not-steady-state (not to mention multi-bar OSes).
I think maybe the right idea is to go look at factory boosted
GM cars that use our kind of PCMs, for where their IAT sits.
Duplicate, and then deal with the tuning.
but I've never seen anyone say just where in a boosted
lineup, the IAT ought to be - what it ought to measure.
I imagine that trying to use IAT in the air after the
impeller is a bad idea, because IAT is slow and would be
impossible to rely upon outside steady-state, while speed
density (where IAT matters big time) is where you go in
not-steady-state (not to mention multi-bar OSes).
I think maybe the right idea is to go look at factory boosted
GM cars that use our kind of PCMs, for where their IAT sits.
Duplicate, and then deal with the tuning.
10-06-2015, 04:29 AM
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than you for the response.
can you elaborate on what you mean by iat is slow?
when reading it in both hptuners and phone obd2 reader the ait sensor reads/change air temp almost instantly. what i mean is i can be sitting around at 100* and go wot where my meth kit would spray and instantly go down in the 60-70* or are you talking about how the computer respond to iat?
in a boosted application i cant see it being located anywhere else other than after the impeller.(which would give the most accurate reading of the actual air temp.) putting it before would mean it wont read them temp change due to the charger.
with methanol injection it really limits the location options since i want it to read the temp change due to the methanol inj.
ive also converted supras before to SD and even hks calls for the iat sensor to be right before the TB. but ill definitley will look up what you suggested though thank you
can you elaborate on what you mean by iat is slow?
when reading it in both hptuners and phone obd2 reader the ait sensor reads/change air temp almost instantly. what i mean is i can be sitting around at 100* and go wot where my meth kit would spray and instantly go down in the 60-70* or are you talking about how the computer respond to iat?
in a boosted application i cant see it being located anywhere else other than after the impeller.(which would give the most accurate reading of the actual air temp.) putting it before would mean it wont read them temp change due to the charger.
with methanol injection it really limits the location options since i want it to read the temp change due to the methanol inj.
ive also converted supras before to SD and even hks calls for the iat sensor to be right before the TB. but ill definitley will look up what you suggested though thank you
10-10-2015, 08:11 PM
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IAT has a thermal time constant. This varies with how it's
encapsulated, primarily. Big bulb is slower than small. The
logs I've looked at, way back when, showed me the IAT
moving pretty slowly toward ambient from a heat soaked
position over the course of some tens of seconds. Even
1 second from "steady state 1" to "steady state 2" is a
lifetime, if you're facing high-boost knock conditions.
"Almost instantly" needs to be judged on the motor's
terms.
I've never seen a good exposition of how the IAT is
worked into the speed density equation, which uses
manifold pressure ( a "different gas" than before the
TB; I imagine there may be some scaling of temp
(absolute, figured from IAT) by something like
(MAP/BARO) to get a calculation of air temp on the
other side of the throttle valve, but this is only my
conjecture. A boosted system where the analogue
of BARO is really the impeller outlet, would not have
a consistent BARO to use in that way, and no data
for an alternative. So what's the deal and where's the
right air temp to sense? I've got more questions than
answers, other than the idea of emulating some
factory scheme (but maybe that PCM has a whole
different scheme for figuring air mass in speed density
mode, or maybe only uses MAF for boost by design,
and on big motors with more than the MAF can follow,
what then?
encapsulated, primarily. Big bulb is slower than small. The
logs I've looked at, way back when, showed me the IAT
moving pretty slowly toward ambient from a heat soaked
position over the course of some tens of seconds. Even
1 second from "steady state 1" to "steady state 2" is a
lifetime, if you're facing high-boost knock conditions.
"Almost instantly" needs to be judged on the motor's
terms.
I've never seen a good exposition of how the IAT is
worked into the speed density equation, which uses
manifold pressure ( a "different gas" than before the
TB; I imagine there may be some scaling of temp
(absolute, figured from IAT) by something like
(MAP/BARO) to get a calculation of air temp on the
other side of the throttle valve, but this is only my
conjecture. A boosted system where the analogue
of BARO is really the impeller outlet, would not have
a consistent BARO to use in that way, and no data
for an alternative. So what's the deal and where's the
right air temp to sense? I've got more questions than
answers, other than the idea of emulating some
factory scheme (but maybe that PCM has a whole
different scheme for figuring air mass in speed density
mode, or maybe only uses MAF for boost by design,
and on big motors with more than the MAF can follow,
what then?
10-13-2015, 04:17 AM
#5
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IAT has a thermal time constant. This varies with how it's
encapsulated, primarily. Big bulb is slower than small. The
logs I've looked at, way back when, showed me the IAT
moving pretty slowly toward ambient from a heat soaked
position over the course of some tens of seconds. Even
1 second from "steady state 1" to "steady state 2" is a
lifetime, if you're facing high-boost knock conditions.
"Almost instantly" needs to be judged on the motor's
terms.
I've never seen a good exposition of how the IAT is
worked into the speed density equation, which uses
manifold pressure ( a "different gas" than before the
TB; I imagine there may be some scaling of temp
(absolute, figured from IAT) by something like
(MAP/BARO) to get a calculation of air temp on the
other side of the throttle valve, but this is only my
conjecture. A boosted system where the analogue
of BARO is really the impeller outlet, would not have
a consistent BARO to use in that way, and no data
for an alternative. So what's the deal and where's the
right air temp to sense? I've got more questions than
answers, other than the idea of emulating some
factory scheme (but maybe that PCM has a whole
different scheme for figuring air mass in speed density
mode, or maybe only uses MAF for boost by design,
and on big motors with more than the MAF can follow,
what then?
encapsulated, primarily. Big bulb is slower than small. The
logs I've looked at, way back when, showed me the IAT
moving pretty slowly toward ambient from a heat soaked
position over the course of some tens of seconds. Even
1 second from "steady state 1" to "steady state 2" is a
lifetime, if you're facing high-boost knock conditions.
"Almost instantly" needs to be judged on the motor's
terms.
I've never seen a good exposition of how the IAT is
worked into the speed density equation, which uses
manifold pressure ( a "different gas" than before the
TB; I imagine there may be some scaling of temp
(absolute, figured from IAT) by something like
(MAP/BARO) to get a calculation of air temp on the
other side of the throttle valve, but this is only my
conjecture. A boosted system where the analogue
of BARO is really the impeller outlet, would not have
a consistent BARO to use in that way, and no data
for an alternative. So what's the deal and where's the
right air temp to sense? I've got more questions than
answers, other than the idea of emulating some
factory scheme (but maybe that PCM has a whole
different scheme for figuring air mass in speed density
mode, or maybe only uses MAF for boost by design,
and on big motors with more than the MAF can follow,
what then?
in your example of heat soak transition. did it happen to also inject 50/50 just before the IAT?
i honestly never watched my IAT until i had to move it in a heatsoak prone location.
I use to see a small knock under wot that i tried tuning out but as it turns out i just wasnt injecting enough at 19psi. now with 14gph and a low meth activation. same tune and no knock thats even on a hot 100* california weather. so far i have not seen any knock under boost with the setup.
im not sure how familiar you are with SD but heres what little bit i know. you probably already know this if not more since I didnt really understand your technical explanation up there ^^
but anyways heres how i understand it. instead of being measure by the maf(which is removed due to the switch)
the SD uses calculation based on the ideal gas law. pv=nRT. pressure is from the map and Temp is an estimation of what would be the temperature at the cylinder.(using IAT)
then this is were the VE correction comes into play. basically allows you to correct what is being "seen" vs what is actually coming in.
non technical but thats how it makes sense in my head. so ideally you want the temp probe at the cylinder. since thats not possible the next best place is after the meth so when the meth sprays and cools down the air temp it can factor that into the equation.
as far as the cap/maf limit. i always though that was one of the advantage of SD. some maf tops out early on and SD was one of the way around it.
10-13-2015, 12:12 PM
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but anyways heres how i understand it. instead of being measure by the maf(which is removed due to the switch)
the SD uses calculation based on the ideal gas law. pv=nRT. pressure is from the map and Temp is an estimation of what would be the temperature at the cylinder.(using IAT)
then this is were the VE correction comes into play. basically allows you to correct what is being "seen" vs what is actually coming in.
the SD uses calculation based on the ideal gas law. pv=nRT. pressure is from the map and Temp is an estimation of what would be the temperature at the cylinder.(using IAT)
then this is were the VE correction comes into play. basically allows you to correct what is being "seen" vs what is actually coming in.
and all in the same volume). Trouble is, you want -manifold-
temp and you get instead -inlet- temp, from a different
place at different pressure, and then you rub that together
with the MAP and get what, exactly? To turn inlet temp
into manifold temp, somebody somewhere gotta do some
figgerin'.
All I know is, it's not that straightforward. I have zero
clue about the PCM algorithm's methods.
Spraying methanol, like spraying nitrous, can directly
affect the IAT reading and differently than it affects
the actual air mass temp. All repending on your aim,
whether it hits the IAT sensor directly at all, too much
or just right.
But as you can see I've got more questions than answers.
