IAT heat soak

[samh_08]

Yes boys, I searched ;). I am having a little bit of an issue keeping my BENs consistent with my IAT sensor getting heat soaked. I know I will always have some heat soak, but Im talking 120*F when ambient is ~70. This happens when I shut it down and let it sit.. Eventutally the IAT comes down to where it should be (also giving me proper BENs) but it takes 5-10 mins of driving. :doh2:

Now my question is, it there any effective way of tuning this without the use of COS5 table A0014 or reloctating the sensor (I dont believe it would be an accurate example of the air actually entering the throttle body)

Let me know what you guys think,
Thanks!

[SSpdDmon]

Yes boys, I searched ;). I am having a little bit of an issue keeping my BENs consistent with my IAT sensor getting heat soaked. I know I will always have some heat soak, but Im talking 120*F when ambient is ~70. This happens when I shut it down and let it sit.. Eventutally the IAT comes down to where it should be (also giving me proper BENs) but it takes 5-10 mins of driving. :doh2:

Now my question is, it there any effective way of tuning this without the use of COS5 table A0014 or reloctating the sensor (I dont believe it would be an accurate example of the air actually entering the throttle body)

Let me know what you guys think,
Thanks!
Re-locate the sensor. ;)`

[GAMEOVER]

Re-locate the sensor. ;)`

I agree...:D

[ringram]

How do you know thats not just heatsoak to the intake air at low airflow?
Otherwise why not just mount it right out of the airflow behind the bumper etc.
What you want is for it to accurately track intake air temp even if its heatsoaked.

Look at the charge blend factors and tables. In theory thats where it should be modelled. I think the A0014 and similar tables are just an easier way to fudge it.

Hell on the E38 I used Injector flow vs IAT to hack it into shape. But Id much rather figure out the airflow vs charge blend factoring, but it seems there is a table or two missing. Therefore my airmass calculations have gone out the window because Ive hacked injector flow :(

All very sad.

[SSpdDmon]

How do you know thats not just heatsoak to the intake air at low airflow?
Otherwise why not just mount it right out of the airflow behind the bumper etc.
What you want is for it to accurately track intake air temp even if its heatsoaked.

Look at the charge blend factors and tables. In theory thats where it should be modelled. I think the A0014 and similar tables are just an easier way to fudge it.

Hell on the E38 I used Injector flow vs IAT to hack it into shape. But Id much rather figure out the airflow vs charge blend factoring, but it seems there is a table or two missing. Therefore my airmass calculations have gone out the window because Ive hacked injector flow :(

All very sad.
I think the effect is very minor. Air...or should I say the gases that make up our atmosphere...are very poor conductors of heat.


Heat conductance occurs when two atoms or molecules interact with one another. This means that they must be reasonably physically close to one another. Because the density of a gas is so much lower than that of a solid or liquid, it will not conduct heat well.

I don't think that the air coming in the intake is around long enough to be altered much. Stagnant under-hood airflow (like when a car sits at idle) will start to warm up similar to the way your oven operates in your kitchen. Therefore, it's natural to see a slight-moderate increase in intake temps over ambient temps when a car isn't moving. However, other parts get hot too. Granted some are plastic and some are metal…they are still much better conductors of heat. Since these parts typically house the IAT sensor, the sensor is inevitably going to confuse the heat radiating off of them as the incoming air temps getting much warmer.

That being said, it’s also been my experience that the LSx motors respond on the lean side to higher temps and on the rich side to cooler temps. So, if you’re still reading and are waiting for me to get to my point…here it is. If the PCM thinks the air entering the engine is denser than it actually is, that’s fine with me. I’d rather err on the rich side than the lean to avoid detonation, to avoid the PCM from pulling timing, etc. That’s why I suggest (on N/A cars) relocating the sensor to just in front of the filter, suspended by fishing string, and a good 3” away from anything solid.

[SSpdDmon]

The air itself won't be affected much but the sensor will be.
The sensor is sitting in the intake tract and depending on
where it is placed it can constantly see higher temps than ambient.

Example: AN LS1 Fbody IAT is usually about 10° above ambient on a "warm" day
this can sky rocket while idling or after a restart even if ECT has dropped.
My point exactly...the sensor "thinks" the air is warmer when in actuality, it probably isn't much warmer at all. I'd be willing to bet the temp of the air under the hood at idle plus a few degrees is truly what the PCM should be reading. So like I said above, I'd rather err on the safe side, say screw those few degrees, and just go with under hood temps.

[swingtan]

I've done a fair amount of logging with different intakes and have seen some interesting things occurring. All cars are Holdens, but the intakes differ, here's just a few examples.


OTR with IAT set toward the front of the unit: In this car I have seen the IAT rise when the car is stationary and idling. the hot air rising from the radiator was being picked up by the OTR and showing on the IAT. As soon as the fans turned on, the IAT dropped as the warm air was pulled through the radiator and away from the intake.
VZ with MAF and stock air box: This is my car and has lots and lots of data logged on it. I also ran a thermometer inside the air box to see the difference between temps. Because of the position of the stock intake, it would easily pick up hot air from in front of the radiator, especially if the air con was on. During summer it was not unusual to see 70'C+ inside the air box. the MAF would always read 5' to 10' warmer while cruising and much more if stuck in traffic. It took a long time to cool everything down once it was hot.
VZ with modded MAF and stock air box: With some minor mods to the MAF, I found that cool down times reduced and the temp difference between the air box and the MAF also came down. More changes to the MAF saw the MAF reading within 5' to 7' of ambient on a cruise, but it still suffered heat soak when in traffic. It was not too bad though and I'd have been happy to keep it as it was. At times the MAF was reading below the temp in the air box as the thermometer in the air box would get heat soak.
VZ with OTR and MAF: Current setup, and obviously the best so far. Yes, it still suffers heat soak but the temps drop rapidly once moving. At the moment it's easy to have IAT's within 2' or 3' of ambient on a cruise.


I know many people just hang the IAT out in the air somewhere near the intake, but I prefer to run the IAT in the intake air flow. It the intake is heat shielded, then soak is not as much of an issue and correct fueling should occur. at low speeds, where airflow is minimal, there is much more of a chance of the air warming in the intake pipes. I'd like to know the ECM is measuring this. If you just care about WOT, then of course there is little time for the intake air to heat up.

Finally, if you get your IAT corrections set right and log over a decent time frame, then any heat soak issues should be averaged out. I've found that a single log of 1 or 2 hours driving works much better than 6 to 10 separate 10 min logs.

Simon.

[eficalibrator]

Re-locate the sensor. ;)`
I disagree, see below...

How do you know thats not just heatsoak to the intake air at low airflow?
Otherwise why not just mount it right out of the airflow behind the bumper etc. What you want is for it to accurately track intake air temp even if its heatsoaked.

Look at the charge blend factors and tables. In theory thats where it should be modelled.
...and it is modeled that way from the factory. There is some very real change in the actual aircharge temperature due to warming from underhood components. The factory cal goes a step further and continues to model the heating of the air from the intake port (which is at least at coolant temp) as well. The whole point is to accurately model what's really going into the cylinders, not what's happening outside.

I think the effect is very minor. Air...or should I say the gases that make up our atmosphere...are very poor conductors of heat.
Poor conductor of heat, yes; but they also have very low mass (compared to anything solid around them) which makes them far easier to change the delta-T in short order.


I don't think that the air coming in the intake is around long enough to be altered much. Stagnant under-hood airflow (like when a car sits at idle) will start to warm up similar to the way your oven operates in your kitchen. Therefore, it's natural to see a slight-moderate increase in intake temps over ambient temps when a car isn't moving.
This is precisely what you should see modeled in the factory biasing tables. The effect is smaller at higher flow rates for a reason.


I know many people just hang the IAT out in the air somewhere near the intake, but I prefer to run the IAT in the intake air flow. It the intake is heat shielded, then soak is not as much of an issue and correct fueling should occur. at low speeds, where airflow is minimal, there is much more of a chance of the air warming in the intake pipes. I'd like to know the ECM is measuring this. If you just care about WOT, then of course there is little time for the intake air to heat up.
Agreed. If you're trying to do is keep it from pulling timing because you think you need more, there are other tables to use to increase ignition advance. Although, if the air really is warmer entering the cylinders, you'll find that it won't need as much timing to hit either MBT or the knock limit.


Finally, if you get your IAT corrections set right and log over a decent time frame, then any heat soak issues should be averaged out. I've found that a single log of 1 or 2 hours driving works much better than 6 to 10 separate 10 min logs.
Even better, perform steady state testing at a single temperature and see the effects once things stabilize. ;)

[redhardsupra]

Even better, perform steady state testing at a single temperature and see the effects once things stabilize. ;)

Greg, I agree with everything, except for this last thing--the real world has more than one air temperature, so wouldnt calibrating at that one stable condition be correct only at that one condition, and be wrong at all others?

[eficalibrator]

Greg, I agree with everything, except for this last thing--the real world has more than one air temperature, so wouldn't calibrating at that one stable condition be correct only at that one condition, and be wrong at all others?
Not if you perform most of your testing at the nominal temp that all the VE tables are corrected to. Even better, follow that up with a series of measurements at other temps (which is admittedly not doable in most performance shops on a single day) so that you can check the temp correlation.

[redhardsupra]

what is the nominal temp?

how are the multiple measurements gonna help me, if the biasing mechanism is highly nonlinear, and on some platforms also time-dependent?

[swingtan]

What a lot of people forget, is that your AFR's will change a fair bit with IAT. Generally, the warmer the air, the leaner the mixtures get ( all else being equal ), so when setting up the VE table you MUST either....


Keep the IAT's as stable as possible, centered around the average mean temperature that you normally expect.
Setup the IAT correction so that any changes in IAT are automatically corrected for in the fueling.


Doing long logs where the car is constantly moving will reduce the effects of heat soak on IAT and help maintain a more constant fueling environment to get a good VE. Short dives will tend to have way too much start / stop driving to get decent data anyway, so the long drives fix 2 problems at once.

You can of course, correct the IAT drift, which is what I did with my car. Admittedly it's an E38 and the corrections are done differently to the LS1, but the concept is the same. Here's a pic of what my AFR vs. IAT was like before setting up the correction....

http://farm3.static.flickr.com/2455/3705529510_4b6228961b_b.jpg

You can see that with no correction, the AFR's lean out as the IAT increases. In this case the car was just idling in the drive way and I used the heat-soak to warm the incoming air. This is a good example of how the intake air will be heated by the intake.

In the E38, the adjustment are made to the injector flow tables to correct for IAT changes. I'm not sure if there is an option for adjusting the stock LS1 OS's but in CO3, you use A0014 to correct. Here's what I ended up with for my E38....

http://farm3.static.flickr.com/2490/3705529522_f9e5fd3f66_o.jpg

The results of the changes made a big difference to the overall stability of the fueling as the IAT changed. Here's the finished product....

http://farm3.static.flickr.com/2553/3705529518_f65cbc1ba5_b.jpg

Note that all I had done was the correction for IAT and not altered the VE. The slight rise and fall of the WB signal is the thermo fans turning on / off and altering the MAP values.

Simon.

[WeathermanShawn]

Greg, any chance we will ever see affordable software that will model a relatively accurate VE Table?

Lately I have been experimenting with using EFILive's VE % calculation. Uses MAF Hz vs users 'calibrated' MAF flow (g/s), IAT, engine size, etc. I have read some of your comments that essentially MAF based airflow and Speed Density airflow in an ideal world be virtually identical..(I.E. if the MAF fails etc..)

I just think for a MAF-based car people spend countless hours doing a VE Table and usually not under ideal conditions. Then they return to MAF and closed-loop and spend more hours working MAF. Then when they 'combine' the two as a system, it does not always 'work' (airflow model and/or fueling still not accurate). Same arguments always appear on IAT and 'heat-soak'.

Any thoughts?

[mr.prick]

What a lot of people forget, is that your AFR's will change a fair bit with IAT. Generally, the warmer the air, the leaner the mixtures get ( all else being equal ), so when setting up the VE table you MUST either....


Keep the IAT's as stable as possible, centered around the average mean temperature that you normally expect.
Setup the IAT correction so that any changes in IAT are automatically corrected for in the fueling.


Doing long logs where the car is constantly moving will reduce the effects of heat soak on IAT and help maintain a more constant fueling environment to get a good VE. Short dives will tend to have way too much start / stop driving to get decent data anyway, so the long drives fix 2 problems at once.

You can of course, correct the IAT drift, which is what I did with my car. Admittedly it's an E38 and the corrections are done differently to the LS1, but the concept is the same. Here's a pic of what my AFR vs. IAT was like before setting up the correction....

http://farm3.static.flickr.com/2455/3705529510_4b6228961b_b.jpg

You can see that with no correction, the AFR's lean out as the IAT increases. In this case the car was just idling in the drive way and I used the heat-soak to warm the incoming air. This is a good example of how the intake air will be heated by the intake.

In the E38, the adjustment are made to the injector flow tables to correct for IAT changes. I'm not sure if there is an option for adjusting the stock LS1 OS's but in CO3, you use A0014 to correct. Here's what I ended up with for my E38....

http://farm3.static.flickr.com/2490/3705529522_f9e5fd3f66_o.jpg

The results of the changes made a big difference to the overall stability of the fueling as the IAT changed. Here's the finished product....

http://farm3.static.flickr.com/2553/3705529518_f65cbc1ba5_b.jpg

Note that all I had done was the correction for IAT and not altered the VE. The slight rise and fall of the WB signal is the thermo fans turning on / off and altering the MAP values.

Simon.
Very nice work!

[redhardsupra]

Simon, what's your reason for adjusting IFR based on IAT? do you think the flow rate actually changes or is just a hack to see if it works?

[swingtan]

the E38 has no COS that allows us to correct the VE for IAT changes ( A0014 in the LS1 COS 3 ) so if you want to run MAFless, you need some way of correcting the fueling for changes in IAT. The only table that comes close to this is the IFR vs. IAT table. No, I don't think that IFR actually changes with IAT, but this table does allow us to make IAT based corrections when the MAF is not used.

Simon

[redhardsupra]

isnt the bias supposed to take care of changes in IAT? why not experiment with that?

[5.7ute]

What a lot of people forget, is that your AFR's will change a fair bit with IAT. Generally, the warmer the air, the leaner the mixtures get ( all else being equal ),

Isnt that the wrong way round Simon? Hotter air will be less dense so the same amount of fuel will cause a rich mixture. It is only when the IAT reads a hotter than actual aircharge temp & calculates a smaller fuelmass that a lean condition will result.

[redhardsupra]

which way it's wrong depends on estimation of the temperature based on the biasing. and even then, in extreme cases where IAT climbs much closer to ECT than usual, then the biasing doesn't almost matter, as the final TEMP has to be in between the two temps. this is not an easy thing to think about, there's just too many cases and variables, easy rules of thumb simply dont apply here.

[swingtan]

Isnt that the wrong way round Simon? Hotter air will be less dense so the same amount of fuel will cause a rich mixture. It is only when the IAT reads a hotter than actual aircharge temp & calculates a smaller fuelmass that a lean condition will result.

You would think so.......

Normally, you would think that cooler air, being more dense, would result in a leaner mixture. However there are a few other tables to help do corrections and I get the feeling that they rely heavily on the MAF to keep things in an acceptable range. Once the MAF goes, the parameters are too high and the correction is too much.

I'm not exactly sure of the reasons for it happening, but I've logged the results and they tell me that my mixtures lean out as the IAT rises. I think that the charge blend factors are involved but haven't gone to far in to them.

Simon

[WeathermanShawn]

Isnt that the wrong way round Simon? Hotter air will be less dense so the same amount of fuel will cause a rich mixture. It is only when the IAT reads a hotter than actual aircharge temp & calculates a smaller fuelmass that a lean condition will result.

I think the IAT vs lean/rich argument depends on whether you are keeping a certain volume of air constant.

Intuitively and from practical experience warmer IAT's than expected always leans me out too (when I am running that tune). Warmer air less dense..less fuel...

[5.7ute]

Mmmm..trying to rethink the ideal gas law here. I think the IAT vs lean/rich argument depends on whether you are keeping a certain volume of air constant.

Intuitively and from practical experience warmer IAT's than expected always leans me out too (when I am running that tune). Warmer air less dense..less fuel...

Mick I know what you saying, but I think there is a volume consideration here that maybe someone at this late hour could prove using the ideal gas law. I should know if off the top of my head, but Meteorology and automobile dynamics do not always go hand in hand.

..WeathermanShawn..

I believe that until we can accurately measure the intake aircharge near the valve, with a sensor that isnt prone to inaccuracy due to its own body becoming heatsoaked, we will be constantly chasing our tail. Until then we have the bias tables to estimate the temp as well as misreporting sensors. No wonder we end up pulling our hair out & using what we can to get as close as possible.

[WeathermanShawn]

I believe that until we can accurately measure the intake aircharge near the valve, with a sensor that isnt prone to inaccuracy due to its own body becoming heatsoaked, we will be constantly chasing our tail. Until then we have the bias tables to estimate the temp as well as misreporting sensors. No wonder we end up pulling our hair out & using what we can to get as close as possible.

You said it Mick! So true.

I actually set a new personal IAT 'heat-soaked' record last weekend..167F!. Stuck in traffic going uphill. Had car in closed-loop, so just watched it trim around 14.7 for several hours. MAF flow was down to about 4 g/s for a while.

Still wonder if that really was the temperature of the air going into the manifold.

Great thread. Will be interested to see what conclusions come out of it.

[5.7ute]

You said it Mick! So true.

I actually set a new personal IAT 'heat-soaked' record last weekend..167F!. Stuck in traffic going uphill. Had car in closed-loop, so just watched it trim around 14.7 for several hours. MAF flow was down to about 4 g/s for a while.

Still wonder if that really was the temperature of the air going into the manifold.

Great thread. Will be interested to see what conclusions come out of it.

Regards.

..WeathermanShawn..

Yikes. I dont believe I have had IAT's that high here even in the middle of summer. Mind you peak hour traffic here would be a hardware store parking lot to you guys.

[swingtan]

I have seen IAT's well over 70'C here in Melbourne, Aircon on mid summer and stuck in traffic. It does happen so I'd like to be able to measure it. For the correction issues, I wrote about them in my E38 VVE guide....

http://download.efilive.com/Tutorials/PDF/Virtual%20VE%20Adjustment%20Tutorial.pdf

See page 7

I would think that if a similar approach was done for the LS1 PCM, that the results would be similar and give a much steadier reading for VE adjustments. People comment on how difficult it can be to adjust the VVE in the E38, but I've found that setting up the IAT correction and then performing a couple of decent log runs, makes the job quite easy.

Simon.

[eficalibrator]

Greg, any chance we will ever see affordable software that will model a relatively accurate VE Table?
I honestly think the tools are already sitting in front of us. Too many people are just looking for shortcuts and end up taking a very long way around to still get a compromised answer.

If you perform most of your MAF and VE measurements and corrections:
1) on a loaded dyno
2) in a single session where ambient and inlet temps are stable
3) by taking measurements in steady state where average logged lambda error equals current lambda error in that cell
4) work with the factory IAT location and biasing tables to start
and...
5) apply changes to the MAF or VE surface (even if it's "virtual") that are smooth and progressive

...then you should end up with a fundamental air model that's pretty close. You may never have 1% accuracy at extreme inlet temps, but that's what closed loop trims are for.

The shortcut of just logging while driving opens the door for variables like cooling airflow, ambient temp, underhood temp, water splash, transient fuel delivery (fuel to wall impact/evap factors) skewing etc. It's far more difficult to develop a good base tune on the street. I have found that two hours of good dyno time can save two weeks or more of street tuning headaches on a single car. It's not that hard to find a loaded dyno any more, just bite the bullet and use one. You'll be surprised how much easier other things get when you have the fundamental air model done right.

[mr.prick]

It's not that hard to find a loaded dyno any more, just bite the bullet and use one.
There is a nice one on ebay right now, too bad I don't have a place to put it. :)

[WeathermanShawn]

I am sure a lot of people do not totally understand the pitfalls of using 'street tuning' exclusively.

Dyno is best.

[joecar]

I agree, tuning on the street has too many variables (not to mention other distractions).

[mr.prick]

It can be fun tho.
http://smiliesftw.com/x/3gears.gif

[WHYTRYZ06]

Thank god for a0014...lol

[mistermike]

I believe that until we can accurately measure the intake aircharge near the valve, with a sensor that isnt prone to inaccuracy due to its own body becoming heatsoaked, we will be constantly chasing our tail. Until then we have the bias tables to estimate the temp as well as misreporting sensors. No wonder we end up pulling our hair out & using what we can to get as close as possible.

Well, I'm almost there, with a cruel twist. I'm running a Starr supercharger setup with an IAT sensor literally stuck in one of the intake ports. The bad news is that it's a brass threaded sensor screwed into an aluminum manifold. I never see anything below about 115 F and to add insult to injury, as with any F/I setup, I'm constantly "modulating" my IAT with the heat generated by the compressor. Stuck in traffic, fuhgettaboutit. DELCO is probably the only guy equipped to make sense of something like this, since he has the same setup, and I believe he invented the A0014 table anyhow.

[98 tigershark]

Place the sensor by the air filter if you have not already as the motor super heats the motor compartment air and the air by your filter is the accurate intake air temp no mater how you look at it.
98 tigershark

[mistermike]

Place the sensor by the air filter if you have not already as the motor super heats the motor compartment air and the air by your filter is the accurate intake air temp no mater how you look at it.
98 tigershark

The combustion chamber is a long way from the air filter. There is ample opportunity for the temps to change along the way. The air/fuel molecules detonating in the combustion chamber don't care a bit what the temperature used to be when they started their journey.

[redhardsupra]

The combustion chamber is a long way from the air filter. There is ample opportunity for the temps to change along the way. The air/fuel molecules detonating in the combustion chamber don't care a bit what the temperature used to be when they started their journey.
absolutely correct!

[98 tigershark]

I believe the question was IAT heat soak.
What you are talking about is an entirely different issue. If you want the correct air temp that the car is taking in then the sensor needs to be next to the air intake filter. The molecule thing sounds impressive and is something to consider in the start up table but not the IAT as the question again was heat soak and the IAT sensor, right. After all the IAT temp is the IAT temp not the valve temp and the density of molecules as once started the IAT has priority on most all 1997 to 2005 PCMs
98 tigershark

[joecar]

The PCM is using IAT (and other values) to estimate how much air just went in... so while the molecules themselves don't care what temperature they started with (at the IAT sensor, a long way away from the CCs), the number of molecules is dependent on the IAT (and a few other things).

[Chevy366]

Why not have dual IATs then , one at the filter and then one at TB ?
Like I have seen , some older models have the IAT in the intake manifold behind the TB , couldn't get much better than that , but yet they moved the IAT out to the filter location .

[redhardsupra]

yes, you can fix heatsoak, but in the process completely lose the point of having an IAT. you're supposed to be estimating temperatures of the airmass in the intake, not air outside, that's just called the ambient thermometer ;)

[98 tigershark]

Joe and Red hard Supra are right I think. The IAT on most 1997-05 PCMs is to do a few things and does have a high priority in the computations. I thought heat soak was when the O2 sensors are to warm to accurately communicate with the PCM. The IAT/ETC AND THE BARO blend determine the amount of air density entering the cylinder or known as the charge temperature.
98 tigershark

[Highlander]

I think the effect is very minor. Air...or should I say the gases that make up our atmosphere...are very poor conductors of heat.


Really?

Hmm.... I thought it was an excellent conductor of heat because of the amount of air you can push through.... Otherwise.. With what does the water get cooled? Yourself for that matter and in the end old air cooled engines?

I mean... If you go down the track with your IATs running on the 140s the change in temperature of IAT will be more of an impact than a difference in BENs in the car's overall power.

I've had quite a lot of heat soaking, specially before entering the lane to race and I definitely FEEL the car a LOT slower than on the street. That closely matches the heatsoaking of all the internal components.

I have done many tests... Be it, not my typical chemical tests, but overall testing to show the effects of a colder intake vs IAT in HP. Even though with higher speeds the time it has to impact the air entering the cylinders should be small, you will get knocking if the intake is hot and the power gets reduced if the intake is hot.

Aside from that... Even on the dyno I can't run as much timing as I do on the street. Knock always appears. Maybe I'll do a complete test with test data and everything to show for this.

[98 tigershark]

For what it is worth here is how the PCM thinks about heat soak and IAT/ETC and BARO;
The PCM calculates the charge temperature (in degrees Kelvin) using the following formula
273.15+IAT+((ECT-IAT)*factor) where factor is obtained from this calibration.

At low airflow "factor" is closer to 1 which weights the charge temperature in favour of ECT.
At high airflow (>150g/s) "factor" is closer to 0 which weights the charge temperature in favour of IAT.

The theory being that heat (ECT) is transferred from the heads and manifold after the IAT has been measured and prior to the air entering the cylinder.

If factor is 0, then the charge temperature will be IAT, if factor is 1, then the charge temperature will be ECT, other values for factor will blend the charge temperature between IAT and ECT accordingly.
98 tigershark

[redhardsupra]

tigershark, it's bias not baro.

[98 tigershark]

Sorry,
You are right. The air is thin where I live and I am light headed and the IAT factor is 0.
Thanks
98 tigershark:fluffy:


tigershark, it's bias not baro.

[SSpdDmon]

Really?

Hmm.... I thought it was an excellent conductor of heat because of the amount of air you can push through.... Otherwise.. With what does the water get cooled? Yourself for that matter and in the end old air cooled engines?

I mean... If you go down the track with your IATs running on the 140s the change in temperature of IAT will be more of an impact than a difference in BENs in the car's overall power.

I've had quite a lot of heat soaking, specially before entering the lane to race and I definitely FEEL the car a LOT slower than on the street. That closely matches the heatsoaking of all the internal components.

I have done many tests... Be it, not my typical chemical tests, but overall testing to show the effects of a colder intake vs IAT in HP. Even though with higher speeds the time it has to impact the air entering the cylinders should be small, you will get knocking if the intake is hot and the power gets reduced if the intake is hot.

Aside from that... Even on the dyno I can't run as much timing as I do on the street. Knock always appears. Maybe I'll do a complete test with test data and everything to show for this.
Google "Thermal Conductivity" and get back to me. ;) Why do you think we have double-paned windows with a pocket of air inbetween that helps keep the heat in through the winter months?? It's because air is a decent insulator - not conductor. Why is it on hot days in direct sunlight, you can look at a black car closely and see the heat waves radiating off the surface - yet they don't seem to be concentrated much over a half an inch above the surface??? The reason the air cooled engine works the way it does is because the metal is conducting / transfering the heat from the source and spreading it out over a greater surface area (the numerous fins). That heat is then disapated (sp?) faster. The air passing through is aiding the process - not conducting the heat. Air has a thermal conductivity rating of less than one where as metals (such as aluminum) will be in the hundreds (1xx~2xx).

At the end of the day, it has been my experience that an N/A LS1 works most consistently with the IAT reading actual intake temps (i.e. the temperature of the air as it enters the filter). If you suspend an IAT sensor just in front of the filter on an f-body & away from all other sources of heat transfer, you will see my point. I did this with fishing string so that the IAT was floating just above the washer fluid tank and it worked for me. IMO - this works because the IAT / ECT bias table is compensating for the heat that is exchanged already. If the IAT represents the start of the path and ECT represents the end, then the slower the airflow (just like an oven in your kitchen) passes through the intake the more the air in the intake begins to align with ECT. But just like your oven in your kitchen, the air in the intake doesn't reach that temp instantly. It doesn't stay in the intake long enough to "preheat" to the ECT temp. Now - think about a false start on that path - having a false IAT reading because the sensor is heat soaked. The ECT swing becomes too powerful and the resulting calculation is a lower airmass than actually exists.

That is the point of this whole discussion. The point of my arguement was around accuracy in fueling. Yes - a higher intake temperate will hold less oxygen and therefore make less power. But, a PCM thinking the incoming air has less oxygen then it really does will cause lean conditions, which are either corrected slightly in closed loop operation or thrown out the window in open loop situations. Not to mention, timing is pulled (with stock settings) as IAT's rise, which will kill power as well if it's truly an unnecessary adjustment.

[Highlander]

You have no other way to deal with the intake manifold SOAKING!

We have 100F days and very humid. Cars get very very hot inside that engine compartment, and not only coolant. Even at the track I find it very convenient to have the IAT soak and retard some timing and not get any ping.

[98 tigershark]

I agree. Check out the my post what weighs more a pound of air and then check the post what weights more a fuel. Accuracy in measurement is very important.
98 tigershark :cheers:

Google "Thermal Conductivity" and get back to me. ;) Why do you think we have double-paned windows with a pocket of air inbetween that helps keep the heat in through the winter months???

At the end of the day, it has been my experience that an N/A LS1 works most consistently with the IAT reading actual intake temps (i.e. the temperature of the air as it enters the filter). If you suspend an IAT sensor just in front of the filter on an f-body & away from all other sources of heat transfer, you will see my point. I did this with fishing string so that the IAT was floating just above the washer fluid tank and it worked for me.

The point of my arguement was around accuracy in fueling. Yes - a higher intake temperate will hold less oxygen and therefore make less power. But, a PCM thinking the incoming air has less oxygen then it really does will cause lean conditions, which are either corrected slightly in closed loop operation or thrown out the window in open loop situations.

[SSpdDmon]

Did some editing above - trying to get my mess of a mind on paper. LOL

[joecar]

...
If the IAT represents the start of the path and ECT represents the end...
...


Jeff, thanks for the explanation, that made a few lightbulbs go on regarding IAT/ECT and the speed of the air.

[SSpdDmon]

Jeff, thanks for the explanation, that made a few lightbulbs go on regarding IAT/ECT and the speed of the air.
I had to explain it to myself in order to get it too. LOL

[Mark300]

The shortcut of just logging while driving opens the door for variables like cooling airflow, ambient temp, underhood temp, water splash, transient fuel delivery (fuel to wall impact/evap factors) skewing etc. It's far more difficult to develop a good base tune on the street. I have found that two hours of good dyno time can save two weeks or more of street tuning headaches on a single car. It's not that hard to find a loaded dyno any more, just bite the bullet and use one. You'll be surprised how much easier other things get when you have the fundamental air model done right.

Before I comment, I am a great supporter of Greg, I have bought both books and DVD and have learned a lot. "A must have for beginners".

My question though to Greg (or anyone interested), is regarding factors affecting results, between street and dyno. All these factors can affect you calibration on a dyno, just as much as the street. Temp (IAT heat soak) and air flow on a VERY LONG and EMPTY freeway is much easier to manage than in a dyno. Transient fuel should be no different as it is based on vehicle speed sensor. The key in both street and dyno is stability and steady state on the throttle and rpm range, to give a stable map. That is the main difference where dyno is better. Am I correct in saying this?
Regards

Mark (perfection is a drug, you can never get enough)

[joecar]

...
The key in both street and dyno is stability and steady state on the throttle and rpm range, to give a stable map. That is the main difference where dyno is better. Am I correct in saying this?
...Yes, that is correct... it can be summarized by saying "steady state airmass/airflow".