to calculate engine size, am i wrong with my number...i took 346 and divided it by 12 and got 28.8 cu ft.

then i took that and started with your math.

t-flow=850*28.8/2
tflow was 12240
tmass=12240*.513324*.0780
tmass was 490.08
ve actual=1.24/490.08
ve actual was .002571009
edit ve=002571009*3000
edit ve was 7.713027
something doesnt add up there in my math, but im sure i did something wrong.

no-go, can you shed some light on my math....

thanks

 

*
*
One Cubic Foot = 1728 Cubic inches. Conversion factor - 1 cu.ft./1728 cu.in. So, 346 * 1 cu.ft./ 1728 cu.in. = 0.200 cubic foot. Hope this helps some. Good Luck.
joel
Ooops - I'm not NoGo, but the math is correct. I don't think he'll mind.Sorry NoGo.

 

NoGo,
Okay, let me see if I have this right.
*I log with Wideband and I get correlated data MAP, RPM and Actual AFR. I'll need to run EFILive V concurrently so that I have accurate MAF values ( Ill log MAP, RPM etc so that I can correlate data).
*Then using T-Flow,T-Mass Flow and Actual VE = MAF/T-Mass Flow I get VE-Edit for the cells in the LS1Edit VE table.
*As these new values will be More Accurate the resultant ACTUAL AFR will be closer to the DESIRED AFR of the FUEL/AIR Multiplier Table ( FUEL/AIR Stoich Ratio Table). "Danger, Will Robinson, Danger"!
So, is this right? or is it, as the robot says "Danger", and I shouldn't quit my day job!

I'm off - to try and figure out why my AFR is dropping to 10.0! at idle after 15 min run at operating temps (80*C ECT and 53*C IAT averages).Idles great initially at operating temps....Then when I come to a stop it just goes to ****.
joel

 

That sounds right Binks. Being you have a wideband O2 you'll be able to check the values with both methods. As a side note, you should n't have to shift your VE tables that much even with your cam. If you are making 15-20% changes all over the place (except around idle RPM), this should tell you that something is wrong.

EVIL, Binks was right, your conversion was off. The actual LS1 Edit VE value that you should have ended up with is 1091. This corrolates to a VE value of 36.4%. This is a typical VE value for aftermarket cams due to intake reversion at low RPM.

Good Luck,
Kevin

 

Good info - the software I posted earlier will perform the same calculations for you based on your log file, and handle interpolation, etc. a couple of differences I would like to check with you on though -

when you convert the flow rate (Tflow) to a massflow (Tmass) what is the reason for using a pressure ration? If we use MAP only then you are calculating the VE for the intake after the the throttle blade - if you use Barometric pressure you are getting actual volumetric efficiency with respect to the theoretical max - but I don't see how you can use a pressure ratio? At a minimum the units will no longer work out, as you have lost all your pressure units so can't calculate density any longer? (though I haven't worked back out to see what factors your constant contains, I think the units is going to be a problem regardless)

When I was looking at the models it looked to me like the LS1 used the "classical" VE definition - basically measuring pumping losses of the entire intake. On LT1's you achieve a theoretical model for a stock car that agrees with the values in the table using the MAP value as opposed to barometric though - but on the LS1 with some log files from a stock car (bone stock, maf, filter, etc.) I got within about +=5% of the stock table through calculation using barometric only - and I can't come up with any rational for using a pressure ratio? - the formula I used was

Nv = (2*Ma) / (Ps*Vd*N)

where

Nv= volumetric effeciency
Ma = actual mass of air inducted
Ps = density of air at inlet
Vd = displacement per cylinder
N = Engine speed
and the 2 accounts for 2 intake events per revolution

and Ps = pressure (inlet) / (Rydbergs Constant * Temperature)


And that was my other question - I had good luck using the IAT as the inlet temperature value in the equation above, thus negating the need to bin-sort the temp values and discard them?


But I am glad to hear that it is working in real lift - I don't have a LS1 to test it out on currently so theory only gets you so far

Also my other question was where you got the 30 as the 100$ equivalent for the VE table - I came up with numbers around there, but I couldn't pinpoint it precisely without knowing if the largest values in the stock table correspond to ~100%, or if they are less?




Thanks again for your input!

 

Thanks ChrisB for your Input.

The pressure ratio was used because the constant following it is the density of air at atmospheric pressure. It was just a poor/lazy method to get the actual air denstiy being ingested. I was just too lazy to break out the thermo book and use the proper gas laws, as you did. Thanks for the proper method of doing it.

The $$ number took some time to get. After about a week of hanging over spreadsheets and a calculator I got fed up and decided to calculate out my own VE table (I was trying to remove the MAF from our race car). I got a couple stock cars, and started driving around logging data. I also made it a point to log dyno runs of stock cars. After about a month of sporatically collecting data I sorted it and was able to work out about 75% of an ls1 F-bod VE table. I then overlayed the values that I had obtained onto the LS1 Edit Table and tried to determine a relationship. I was surprised to find out that scaling my numbers from 0 to 3000 yielded the LS1 Edit VE numbers EXACTLY.

I started using 30 to back-calculate and devlope VE tables for cams / speed density mode and such and the value has held up well.

But, as with you, I don't know why it is the 100$ number, but it is defiantly the number.


So with your above input, the VE equation to determine LS1 Edit VE can be more accurately changed to....

Ps = pressure (inlet) / (Rydbergs Constant * Temperature)

Edit Nv = ((2*Ma) / (Ps*Vd*N)) * 3000

Edit Nv = LS1 Edit volumetric efficiency
Nv = volumetric effeciency
Ma = actual mass of air inducted
Ps = density of air at inlet
Vd = displacement per cylinder
N = Engine speed

 

Sounds good, and makes sense! here is the actual formula I use
'MAFFlow in units of grams/second
'RPM as Revolutions Per Minute
'Displacement in units of Cubic Inches
'MAP in units of KiloPascals
'Temp in units of Degrees Centigrade

VE = MAFFlow * (Temp + 273.15) / (Displacement * RPM * MAP) * 212544

That will give you a VE in units of %. So you could use the above formula and multiply it by 30 to get values in "Edit Units"

With MAP in there as a term it should correspond to the forumula NoGo posted above - if it doesn't hopefully someone will let me know!

 

Post deleted by Kaveman42

 

NoGo I'm gonna try doing the VE method you explained above. Thank you very much. now understand why when I made 10% changes in the VE it did not result in a 10%change in my ltrims. As you explained earlier to use the IFR for large ltrim adjustments and the VE for minor adjustsments. Now it all makes more sence

Now all I have to do is right a little piece of code that will read my logs files and spit me out the right answers

 

good gawd i need some pills or something because my brain hurts like hell after readin this.... it will take me a week to study this POST LMAO

very good info!!!!!!!!!!!!!!

 

i just took the math and put it in 4 different calculated pids in efi live and it comes out with the correct number now.

i guess i can ride around now and log my ve so i can put it into edit.

 

Evil - can you post some of your new VE numbers versus the Edit Numbers??
joel

 

But what does it all mean Basil?

 

the actual ve that efi live is showing using the math from above is a little lower across the board. i didnt mess with it too much yesterday because i think i have a vacume leak on my holley intake and i had a to-do list from the wife on top of that.

i will try and run some logs and post them up and then you can see take a look it it, that is if the hurricane doesnt take my house out!

 

What units are the above variables in? I'm trying to crack the above formula

 

Volumetric effeciency is a ratio of massflows - hence unitless. Keep track of them and as long as they cancel out you are fine.

For the Density measurement you can express rybergs constant in whichever units you choose - so just adjust the constant or the units so they all cancel out!

 

huh :wtf: did you just say

 

Great to be an engineer, you guys are actually talking english

 

How did you come up with the 212544 number? maybe that will help me understand things a little better

 

<-math