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Thread: noob needs help with ve tables

  1. #11
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    the file i have linked above is a stock map for a ls1 engined hsv clubsport from 2004. if you look at the upper ranges of the ve table, high load high rpm area's the values are 103-105. now my understanding of how efilive works and the tuning of these vehicles means that you are basically seeing positive pressure ( or in other words boost ) on an na engine. it doesn't make sense to me thats all.

  2. #12
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    Quote Originally Posted by kierancameron View Post
    the file i have linked above is a stock map for a ls1 engined hsv clubsport from 2004. if you look at the upper ranges of the ve table, high load high rpm area's the values are 103-105. now my understanding of how efilive works and the tuning of these vehicles means that you are basically seeing positive pressure ( or in other words boost ) on an na engine. it doesn't make sense to me thats all.
    I am not really sure where you getting that VE Values over 100% are positive pressure or boost (do you have a reference or link?). If you take Joecar's CALC.VE Formula..

    ..VE[g*K/kPa] and VE[%] using pids (assuming engine 5.669L V8): VE[g*K/kPa] = {SAE.MAF.gps}*({GM.DYNAIRTMP_DMA.C}+273.15)*15/({SAE.RPM}*{SAE.MAP.kPa}) VE[%] = {SAE.MAF.gps}*({GM.DYNAIRTMP_DMA.C}+273.15)*3445.2/({SAE.RPM}*{SAE.MAP.kPa}*5.669)..the VE Values are simply Airflow values. To get a VE Value of ~105% at 5200 Rpm's & 100 MAP, DAT=10C, you would need a MAF flow of 330 g/s.

    For instance, my H/C 2002 Camaro gets close to that Value in the upper regions. However, my VE Table approximates what a dyno curve of it looks like. It peaks ~4800-5200 Rpms then falls off.

    In reality at that point with the Tune you posted, you are all MAF anyway. So unless you are Tuning SD, why worry about it.

    The bottom line is that VE Values over 100% have nothing to do with positive pressure or boost. You need a lot of work done on a vehicle to hit it..

    2002 Black Camaro Z-28 M6 Hardtop 11.0:1CR 425HP/410TQ SAE (400TQ@3500RPM)
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  3. #13
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by kierancameron View Post
    the file i have linked above is a stock map for a ls1 engined hsv clubsport from 2004. if you look at the upper ranges of the ve table, high load high rpm area's the values are 103-105. now my understanding of how efilive works and the tuning of these vehicles means that you are basically seeing positive pressure ( or in other words boost ) on an na engine. it doesn't make sense to me thats all.
    As Shawn said, that does not imply positive pressure... it simply means the PCM calculates cylinder airmass greater than what the cylinder can actually hold;

    GM may or may not necessarily correctly model the cylinder airmass.

    I don't like viewing VE in % units, I instead prefer g*K/kPa.



    As Shawn said, a correctly modeled VE table looks like the TQ curve from a dyno pull.

  4. #14
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    thats what i would expect as well. ve should be more or less proportional to map and follow the torque curve. but if i look at the stock calibration of my 2000 c5 corvette, its quite different: ve is 91% @ 50 kpa and 99% @ 100 kpa. shouldnt it have doubled? at 100 kpa it rises to 99% @ 5200 rpm (far beyond peak torque) and stays at that value at higher rmp, while cylinder filling decreases for sure.

    i guess this is what op was saying. so what am i missing here? is that a trick to enrichen the mixture? but commanded lambda doesnt support this, it doesnt change much at highrer loads and rpm.

    edit: i was just able to look at 2002 os 12212156 and interestingly there ve peaks at 4400 rpm (105%) and falls to 88% at 6400 for 100 kpa. where does the difference come from?
    Last edited by dian; June 19th, 2015 at 08:07 AM.

  5. #15
    Joe (Moderator) joecar's Avatar
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    Quote Originally Posted by dian
    thats what i would expect as well. ve should be more or less proportional to map and follow the torque curve. but if i look at the stock calibration of my 2000 c5 corvette, its quite different: ve is 91% @ 50 kpa and 99% @ 100 kpa. shouldnt it have doubled? at 100 kpa it rises to 99% @ 5200 rpm (far beyond peak torque) and stays at that value at higher rmp, while cylinder filling decreases for sure.

    ...
    TQ is proportional to VE.

    But VE is not proportional to MAP...

    to start with, flowrate (air flowing past open valve into cylinder) is proportional to the squareroot of pressure...
    and then there are various complications (restrictions to flow, venturi effect where port narrows, ...) all of which make the MAP-to-VE relationship complex (not linear, but polynomial of decaying exponential terms)...


    look at any VE table, compare 50% to 100%, you will see there is no simple evident relationship;

    ( BTW: I like to look at VE in g*K/kPa units, this form of VE is simply cylinder fill airmass normalized for temperature and pressure; the V7 tunetool has an option setting for viewing VE in g*K/kPa units ).


    Quote Originally Posted by dian
    ...
    is that a trick to enrichen the mixture? but commanded lambda doesnt support this, it doesnt change much at highrer loads and rpm.
    ...
    I don't understand your question...

    Commanded lambda (I prefer EQR (Equivalence Ratio), EQR = 1/Lambda) is settable in the PE table... if your VE and/or MAF tables are both correct, then you can measure the same lambda in the exhaust gas as the commanded lambda.

    Note that when PE enables, you typically will not be trimming to stoichiometric any more, and if the PE table is richer than stoich (and it should) then it will determine fueling (i.e. PE table will then determine commanded lambda or commanded EQR)

    ( BTW: I like to use EQR for commanded fueling, and Lambda for wideband measured exhaust gas, this way I can avoid confusion in conversation by narrowing down the 4 combinations down to 2 )


    Quote Originally Posted by dian
    ...
    edit: i was just able to look at 2002 os 12212156 and interestingly there ve peaks at 4400 rpm (105%) and falls to 88% at 6400 for 100 kpa. where does the difference come from?
    The VE peak depends on the installed advance of the cam (advancing the cam moves the peak lower, retarding the cam moves the peak higher).

    As engine spins faster, there is less time to ingest a given amount of air, so retarding the cam (or increasing the duration) opens the window wider to allow more time.

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