IAC Effective Area: What am I doing wrong?
Gameover, is there a reference to the tb hole area in the pcm code? And if so is this value subtracted out from the area needed to flow the desired airflow? I'll take as much detail as i can get.
The idea that in one iac step it can open 14 mm^2 of area seems unrealistic to me, but i guess that depends how far the iac plunger moves in 1 step. Anybody know?
The idea that in one iac step it can open 14 mm^2 of area seems unrealistic to me, but i guess that depends how far the iac plunger moves in 1 step. Anybody know?
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Originally Posted by gameover
no probs 
This is not frustrating at all, in fact it's relaxing compared to writing powerpc assembly
although i am starting to draw the line at saying the same thing 3 different ways per thread 
Chris...
This is not frustrating at all, in fact it's relaxing compared to writing powerpc assembly
although i am starting to draw the line at saying the same thing 3 different ways per thread Chris...
FormerVendor
Joined: Jan 2003
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From: Melbourne, Australia
Originally Posted by P Mack
Gameover, is there a reference to the tb hole area in the pcm code? And if so is this value subtracted out from the area needed to flow the desired airflow? I'll take as much detail as i can get.
It's pretty much a totally seperate piece of code that really only interacts with the spark code for the adaptive idle spark, some of the torque estimation code for the AC compensation and if it's ETC then the effective area is translated into a throttle position using a simple scalar and then passed over to the ETC code.
Chris...
I still believe all the zeros at the beginning of the effective area table are there because of the tb hole. For one thing, the stock tb hole size is 4mm right? Which would be about 13 mm^2. Coincidence? Could be but I doubt it. The other reason is, you are saying that from 0 IAC steps to 1 step the opening is effectively the same size as a 14mm^2 hole. That seems like way to big of a difference considering how small an IAC step is. The third reason is like you said, the tb hole size is not accounted for in the code, which makes me believe it is accounted for in the first few columns of this table. I understand what you're saying but i'm not convinced. Although it really only matters conceptually, not so much in the actual tuning process.
P MACK ... I dont think you quite understand why its 0 and then all of teh sudden 12 or 14 mm
if you close the TB...its 0 until you open it.....
when you move it 1 step...it moves and opens x amount of degreres...
1 step is always 1 step.... and its always x amount of degrees of a circular motion...
if 1 step were to equal 10 degrees then it would be teh area = to 10 degrees
area of a circle inreases exponentially as you move its radian points....
but from 0 to 1 wil always be 0 = 0 and 1 =14 on a stock TB...
a larger TB may be 0=0 and 1=20 because the circle is larger so the same 10 degrees of movement has a bigger area
of course I am exaggerating the fact that it does not move 10 degrees...but it helps to look at it like a larger # so our brains see movement when we think of it...
the way I was explained about the hole not being aconted for is because we have RAF tables...
teh idea of all teh other tables is to reduce airflow as things change to get our cars to reset to 0 when totally warmed up and idleing normally.
the PCM treats what it needs to just run with no interaction as 0 and everything else is wht we have all the other tables....
teh TB hole is just not in the code...
why else would we be able to (or even need to) reset the TPS % to 0 if we made a change to how far the blade sat open or for when we dril the TB
with the stock TB and stock table...if you make an adjustment to get the car to idle with drilling the TB or cracking the TB blade and resetting TPS sensor...then we dont need to change the table at all
if you close the TB...its 0 until you open it.....
when you move it 1 step...it moves and opens x amount of degreres...
1 step is always 1 step.... and its always x amount of degrees of a circular motion...
if 1 step were to equal 10 degrees then it would be teh area = to 10 degrees
area of a circle inreases exponentially as you move its radian points....
but from 0 to 1 wil always be 0 = 0 and 1 =14 on a stock TB...
a larger TB may be 0=0 and 1=20 because the circle is larger so the same 10 degrees of movement has a bigger area
of course I am exaggerating the fact that it does not move 10 degrees...but it helps to look at it like a larger # so our brains see movement when we think of it...
the way I was explained about the hole not being aconted for is because we have RAF tables...
teh idea of all teh other tables is to reduce airflow as things change to get our cars to reset to 0 when totally warmed up and idleing normally.
the PCM treats what it needs to just run with no interaction as 0 and everything else is wht we have all the other tables....
teh TB hole is just not in the code...
why else would we be able to (or even need to) reset the TPS % to 0 if we made a change to how far the blade sat open or for when we dril the TB
with the stock TB and stock table...if you make an adjustment to get the car to idle with drilling the TB or cracking the TB blade and resetting TPS sensor...then we dont need to change the table at all
Why are you even talking about throttle position and throttle degrees, i'm talking about IAC position of 1. When the IAC motor moves it doesn't move the throttle plate, it opens a restriction in the iac hole.
The reason the tps is reset to 0 is because if the throttle% is too high the pcm will think you're pressing on the gas and won't adjust back to the idle rpm.
Yes, I understand why Gameover is saying it jumps from 0 to 14. It being the effective area of the IAC passageway, not the throttle blade as you explained. Also, what are you talking about resetting to 0, the idle trims or the desired idle airflow?
The reason the tps is reset to 0 is because if the throttle% is too high the pcm will think you're pressing on the gas and won't adjust back to the idle rpm.
Yes, I understand why Gameover is saying it jumps from 0 to 14. It being the effective area of the IAC passageway, not the throttle blade as you explained. Also, what are you talking about resetting to 0, the idle trims or the desired idle airflow?
Originally Posted by gameover
It's pretty much a totally seperate piece of code that really only interacts with the spark code for the adaptive idle spark, some of the torque estimation code for the AC compensation and if it's ETC then the effective area is translated into a throttle position using a simple scalar and then passed over to the ETC code.
Chris...
Chris...
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Verdad Gallardo I was doing it for a visual to explain why its more as you open it...for thise that dont get it...and havent seen the insides cause they havent looked at it..they have to understand it somehow....
using the TB blade is an easy way to show what it is comparitively doing.....
and helps people understand why 0 is 0 and 1 step is 14 and a big circle help s people visualize....cause its a circular passageway(well...sort of circular anyways..LOL)
using the TB blade is an easy way to show what it is comparitively doing.....
and helps people understand why 0 is 0 and 1 step is 14 and a big circle help s people visualize....cause its a circular passageway(well...sort of circular anyways..LOL)
Ok, i see why you said it, but it's not an exponential jump like you make it sound.
If I went to VCM controls and manually set the iac position to 0, and if my tb set screw was down all the way, all the airflow through the throttlebody should be coming through the tb hole, correct. Which means I would have about 13mm^2 of area for my idle airflow to pass through.
Now I set IAC steps to 1. According to you, I now have an extra 14mm^2 of effective area. In one IAC step i've doubled the area which air can flow through in my tb. That's like drilling an extra tb hole.
Try it. Set your IAC steps to 0, and then to 1. I bet the rpms won't even change. (Hopefully your car can still idle at 0 IAC counts)
If I went to VCM controls and manually set the iac position to 0, and if my tb set screw was down all the way, all the airflow through the throttlebody should be coming through the tb hole, correct. Which means I would have about 13mm^2 of area for my idle airflow to pass through.
Now I set IAC steps to 1. According to you, I now have an extra 14mm^2 of effective area. In one IAC step i've doubled the area which air can flow through in my tb. That's like drilling an extra tb hole.
Try it. Set your IAC steps to 0, and then to 1. I bet the rpms won't even change. (Hopefully your car can still idle at 0 IAC counts)
FormerVendor
Joined: Jan 2003
Posts: 525
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From: Melbourne, Australia
Originally Posted by P Mack
What do you mean by it, the desired idle airflow code?
I agree with your previous point that in the end it really doesn't matter, the results just offset the RAF table a little. If you tweak this table you WILL have to revisit your entire RAF table, allow trims to learn again etc.
I only really put this table in for people who were having trouble with aftermarket TB's with screwy IAC passages. Where they were messing with the actual shape of this curve. Some tuners use it as a lower bumpstop on the idle (again don't really recommend this). With the effort you can get the same/better results by messing with the airflow numbers.
Chris...
if your set screw is 0 and IAC position is 0 then no air can get thru unless you count the hole in the TB...
on most aftermarket TB...you dont have a hole..and you either have to drill it or use the set screw to get air for idle....
consider 0 to be 0
if you haev a hole...then you have hole + 0 at 0 steps or hole + 14mm^2 at 1 step
the computer treats the air coming thru the hole as 0...
even though it might be 13mm^2..it has no way to subtract that value...so that value is referenced as 0
if you run a race..and you are the 3rd leg..and it took the first 2 runners 2 minutes each to complete their leg.... your lap time is similar to theirs....then your time is also 2 minutes...not 6 minutes
on most aftermarket TB...you dont have a hole..and you either have to drill it or use the set screw to get air for idle....
consider 0 to be 0
if you haev a hole...then you have hole + 0 at 0 steps or hole + 14mm^2 at 1 step
the computer treats the air coming thru the hole as 0...
even though it might be 13mm^2..it has no way to subtract that value...so that value is referenced as 0
if you run a race..and you are the 3rd leg..and it took the first 2 runners 2 minutes each to complete their leg.... your lap time is similar to theirs....then your time is also 2 minutes...not 6 minutes
Originally Posted by gameover
Yes, actually it's called "IAC airflow".
Originally Posted by soundengineer
if your set screw is 0 and IAC position is 0 then no air can get thru unless you count the hole in the TB...
on most aftermarket TB...you dont have a hole..and you either have to drill it or use the set screw to get air for idle....
consider 0 to be 0
if you haev a hole...then you have hole + 0 at 0 steps or hole + 14mm^2 at 1 step
on most aftermarket TB...you dont have a hole..and you either have to drill it or use the set screw to get air for idle....
consider 0 to be 0
if you haev a hole...then you have hole + 0 at 0 steps or hole + 14mm^2 at 1 step
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Gameover- can I ask you another question? Before and after I changed my IAC Effective Area table my Dynamic Airflow was about .5g/s higher than my Desired Airflow. The IAC was usually at around 35 steps. I would think the PCM would have closed off the IAC more in order to bring the two Airflow values to the same point. Is this a result of not letting the idle trims relearn enough as you said in an earlier post? In other words should I return my Effective Area table to stock, let the idle trims dial themselves in, then tune my RAF table?
FormerVendor
Joined: Jan 2003
Posts: 525
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From: Melbourne, Australia
Originally Posted by Zeus
Gameover- can I ask you another question? Before and after I changed my IAC Effective Area table my Dynamic Airflow was about .5g/s higher than my Desired Airflow. The IAC was usually at around 35 steps. I would think the PCM would have closed off the IAC more in order to bring the two Airflow values to the same point. Is this a result of not letting the idle trims relearn enough as you said in an earlier post? In other words should I return my Effective Area table to stock, let the idle trims dial themselves in, then tune my RAF table?
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I found this info in reply to a question regarding available area from an open throttle. The guys with drilled holes have an easier task, than those using set screw.
A tilted throttle butterfly covers an elliptical crossection. Say the
butterfly is rotated alpha degrees from fully closed. The major axis has
length x and the minor axis is x*cos(alpha). The area of an ellipse with
major axis 2a and minor axis 2b is pi*a*b, so in this case,
pi*x^2*cos(alpha)/4
As a "kludge" or otherwise, setting the IAC zero count at the above open area should work, assuming the formula is correct. Im off to work for the day, so if anyone else wants to crunch the numbers and see if it matches let us know.
Nope dodgy answer I think, crunched a few numbers though and got a mess. Time to give up and just use trial and error
A tilted throttle butterfly covers an elliptical crossection. Say the
butterfly is rotated alpha degrees from fully closed. The major axis has
length x and the minor axis is x*cos(alpha). The area of an ellipse with
major axis 2a and minor axis 2b is pi*a*b, so in this case,
pi*x^2*cos(alpha)/4
As a "kludge" or otherwise, setting the IAC zero count at the above open area should work, assuming the formula is correct. Im off to work for the day, so if anyone else wants to crunch the numbers and see if it matches let us know.
Nope dodgy answer I think, crunched a few numbers though and got a mess. Time to give up and just use trial and error
Last edited by ringram; Jan 13, 2006 at 06:54 AM.
