Notices
Advanced Engineering Tech For the more hardcore LS1TECH residents
Sponsored by:
Sponsored by:

IAC Math Fun

 
Old 04-26-2019, 05:57 AM
  #1  
TECH Resident
Thread Starter
 
ChopperDoc's Avatar
 
Join Date: Oct 2014
Location: Virginia
Posts: 867
Default IAC Math Fun

So I've been working on an understanding of EXACTLY what the steps in the IAC table correlate to, including how a step change and the amount of air it changes as a result. Obviously bigger throttle bodies will cause different numbers, and I have a way to show this. The PCM does not know this number though, but it can be assumed that when GM programmed the PCM initially, it was well known, so I've used stock values in many assumptions.

Also known, is that the stock TB output hole for the IAC is approximately 310 cubic millimeters, according to the table, and if you calculate the size of the hole, it's relatively close to this number, assuming a square hole, which it is not. Using 25.4mm (1 inch) x 12.7 (1.2") you get 322 mm2... I'd say that's fairly close, baring any other design interference from shape. This happens to be about 0.065% of the total TB blade area, using 310mm2. So that would assume a few more things.

If you take the max MAF calc and divide that into the max TB area of a 78mm TB, you get about 10.8 mm2 per g/s at WOT. Again, assuming the GM numbers. Removing PE from this also makes a change, and this number gets much bigger.

Here is the excel I've been playing around with, using stock data and some of my own from my car, including injector changes. Feel free to experiment with it, I'm still trying to figure these things out in detail because it is one of the few things I still do not fully understand.

I also have injector average and conversion on there. Top row is stock LS1 and bottom is mine, or whatever you plug in. On the top you can see how fast the derivative is too, lol, and now we know it takes about 200 ms for the STIT to react according to that, and the rate it adds air too, over 190-200 ms.
Attached Files

Last edited by ChopperDoc; 04-26-2019 at 06:05 AM.
ChopperDoc is offline  
Old 05-04-2019, 09:22 AM
  #2  
TECH Veteran
iTrader: (22)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 4,792
Default

hey thats really awesome. saved for next time I have to tune a chinese 102mm lol
truckdoug is online now  
Old 05-04-2019, 09:36 AM
  #3  
TECH Resident
Thread Starter
 
ChopperDoc's Avatar
 
Join Date: Oct 2014
Location: Virginia
Posts: 867
Default

I think my calcs are a bit off, but you can see where I'm going with it lol.
ChopperDoc is offline  
Old 05-04-2019, 09:41 AM
  #4  
TECH Resident
Thread Starter
 
ChopperDoc's Avatar
 
Join Date: Oct 2014
Location: Virginia
Posts: 867
Default

I was hoping for some folks to take a crack at it too, and maybe if we put our heads together we can come up with a solid answer as to what the values mean. The other way I was doing it was taking the root of the mm2 and converting that to grams. I'll get back to working on this at some point. I think I'm headed in some sort of direction, not sure if it's the right one lol. I think the biggest thing to do is port out the IAC on the 102's which makes a huge difference from what I've read on that over on the HPT forums. I'm gonna give that a try when I get back stateside and report back on it.
ChopperDoc is offline  
Old 05-04-2019, 04:50 PM
  #5  
10 Second Club
iTrader: (4)
 
Darth_V8r's Avatar
 
Join Date: Jul 2014
Location: My own internal universe
Posts: 6,975
Default

I meant to post up. I was trying to see the math behind 1% throttle stuff. Because the blade is not linear. 5% open does not mean 5% of the area is flowing.
Darth_V8r is online now  
Old 05-04-2019, 04:59 PM
  #6  
TECH Resident
Thread Starter
 
ChopperDoc's Avatar
 
Join Date: Oct 2014
Location: Virginia
Posts: 867
Default

Originally Posted by Darth_V8r View Post
I meant to post up. I was trying to see the math behind 1% throttle stuff. Because the blade is not linear. 5% open does not mean 5% of the area is flowing.
Yes this is true, it would be more of an acceleration based on pressure delta. So basically a slope rate based on how big the area becomes and in what amount of time. I get that, but at or near closed, it won't change too much so I used a simpler model there.
ChopperDoc is offline  
Old 05-04-2019, 05:27 PM
  #7  
10 Second Club
iTrader: (4)
 
Darth_V8r's Avatar
 
Join Date: Jul 2014
Location: My own internal universe
Posts: 6,975
Default

Originally Posted by ChopperDoc
Yes this is true, it would be more of an acceleration based on pressure delta. So basically a slope rate based on how big the area becomes and in what amount of time. I get that, but at or near closed, it won't change too much so I used a simpler model there.
That is true. Basic calculus. Zoom in enough on any curve and it is close enough to linear within a narrow range.
Darth_V8r is online now  
 


Thread Tools
Search this Thread

About Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: