Explain the Volumetric Efficency Table
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Explain the Volumetric Efficency Table 1) What are the units? For example: at MAP = 15 & RPM = 400, I have a value of 1081. What is the 1081?
3) When would I change the table? For example if my car is running rich (negative LTRIMS), would I reduce or increase the values in the relevent cells?
2) Do the values have a linear relationship? For example is a value of 2000 double that of 1000? Will a 5% change produce a 5% change in LTRIMs or a 5% change in A/F ratio at WOT?
TIA <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<small>[ April 12, 2002, 01:07 PM: Message edited by: Ragtop 99 ]</small>
3) When would I change the table? For example if my car is running rich (negative LTRIMS), would I reduce or increase the values in the relevent cells?
2) Do the values have a linear relationship? For example is a value of 2000 double that of 1000? Will a 5% change produce a 5% change in LTRIMs or a 5% change in A/F ratio at WOT?
TIA <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
<small>[ April 12, 2002, 01:07 PM: Message edited by: Ragtop 99 ]</small>
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Re: Explain the Volumetric Efficency Table Do the overwhelming response, <img border="0" title="" alt="[Sad]" src="gr_sad.gif" /> I found the following in an LT1 Edit reference web page.
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> It was determined by John Lamb that the value is defined by the following relationship.
VE = Actual airflow(MAF)
-------------------------------
(RPM/120 * Air Density * 5.733)
Air density can be determined using:
(MAP - Vapor pressure(H2O))
---------------------------
0.287 * IAT(in Kelvin)
This is simply a re-arrangement of PV=nRT (ideal gas law)
When the value in this table is increased at a specific point fueling at that point will be increased, and vice versa. This table is used typically in closed loop mode to adjust the long term fuel trims so they are around 123-125 (Values Appear To Be Specific to LT1) .
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">It's a start, but WTF are units?
<small>[ April 13, 2002, 04:38 PM: Message edited by: Ragtop 99 ]</small>
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> It was determined by John Lamb that the value is defined by the following relationship.
VE = Actual airflow(MAF)
-------------------------------
(RPM/120 * Air Density * 5.733)
Air density can be determined using:
(MAP - Vapor pressure(H2O))
---------------------------
0.287 * IAT(in Kelvin)
This is simply a re-arrangement of PV=nRT (ideal gas law)
When the value in this table is increased at a specific point fueling at that point will be increased, and vice versa. This table is used typically in closed loop mode to adjust the long term fuel trims so they are around 123-125 (Values Appear To Be Specific to LT1) .
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">It's a start, but WTF are units?
<small>[ April 13, 2002, 04:38 PM: Message edited by: Ragtop 99 ]</small>
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Re: Explain the Volumetric Efficency Table Wasn't there a really heated debate about this on the LT1 Edit list earlier this year?
I have seen very few playing with it <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
I have seen very few playing with it <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
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Re: Explain the Volumetric Efficency Table </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ToplessTexan:
<strong>Wasn't there a really heated debate about this on the LT1 Edit list earlier this year?
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I don't know; I found this in a specific document I was linked to.
<strong>Wasn't there a really heated debate about this on the LT1 Edit list earlier this year?
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I don't know; I found this in a specific document I was linked to.
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Re: Explain the Volumetric Efficency Table There was debate as the whether the tables were used in MAF mode in OBD-I computers (at first I thought the were, now I tend to think otherwise).
They are definitely not used in OBD-II LT1 computers.
I highly doubt they are used in MAF mode in LS1 computers, thoughs ome have claimed otherwise. I would submit that they are more than likely there to allow decent operation in SD mode if the maf fails. You can verify rather easily if they have any effect or not - scale the entire table by 130 percent or so and then drive and look for differences in l-trims, etc.
Chris
They are definitely not used in OBD-II LT1 computers.
I highly doubt they are used in MAF mode in LS1 computers, thoughs ome have claimed otherwise. I would submit that they are more than likely there to allow decent operation in SD mode if the maf fails. You can verify rather easily if they have any effect or not - scale the entire table by 130 percent or so and then drive and look for differences in l-trims, etc.
Chris
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Re: Explain the Volumetric Efficency Table </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ChrisB:
<strong>You can verify rather easily if they have any effect or not - scale the entire table by 130 percent or so and then drive and look for differences in l-trims, etc</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">It's good to know there are people braver than me out there <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
<strong>You can verify rather easily if they have any effect or not - scale the entire table by 130 percent or so and then drive and look for differences in l-trims, etc</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">It's good to know there are people braver than me out there <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
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Re: Explain the Volumetric Efficency Table If the table has any effect at all you will simply run rich by a factor of 0-30 percent. It's not going to hurt anything, and in reality you will see no different at all unless your MAF dies.
Chris
Chris
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Re: Explain the Volumetric Efficency Table My LTRIMS are fat and I have already cut my MAF rate by 5%. and I bumped my injector rate by 39% to compensate for 30lb SVOs. Reducing my MAF rate by another 5-10% would make the car WAY lean at WOT, so somewhere the computer needs to be told at part throttle that it is spraying too much fuel. I assumed the VE table was the place to fix it, but maybe I'll tweak the MAF rates at lower end of the spectrum and leave the higher frequencies alone.
BTW, 30% could be enough to flood the engine at start-up if you're rich to start; I'd suggest a 15% change for anyone who is game. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
BTW, 30% could be enough to flood the engine at start-up if you're rich to start; I'd suggest a 15% change for anyone who is game. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
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From: College Station, Tx
Re: Explain the Volumetric Efficency Table Use one of the various injector spreadsheet's to set the proper injector constants
(I have on at http://www.speeddemonmotorsports.com...ectorscale.xls
and John Skiba @ Pace had a nice one out also - both will arrive at correct values
)
You really shouldn't have to change the shape of the MAF transfer function to much - I would try and see if you can scale by a single factor so your l-trims are from -2 to -6 or so.
To cure your WOT worries use the PE vs RPM
Chris
(I have on at http://www.speeddemonmotorsports.com...ectorscale.xls
and John Skiba @ Pace had a nice one out also - both will arrive at correct values
)
You really shouldn't have to change the shape of the MAF transfer function to much - I would try and see if you can scale by a single factor so your l-trims are from -2 to -6 or so.
To cure your WOT worries use the PE vs RPM
Chris
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Re: Explain the Volumetric Efficency Table </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ChrisB:
<strong>Use one of the various injector spreadsheet's to set the proper injector constants
(I have on at http://www.speeddemonmotorsports.com...ectorscale.xls
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">That's what I used. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> Look at the math for SVO 30s using FP = 39 assumption. 1.37 - 1.39 adjustment. I went with 1.39 since I was rich accross the board.
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
You really shouldn't have to change the shape of the MAF transfer function to much - I would try and see if you can scale by a single factor so your l-trims are from -2 to -6 or so.
To cure your WOT worries use the PE vs RPM
Chris </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You're right, I could do that but I doubt the MAF is off that much, especially since it is descreened which if anything would lean it out just a tad. To me, the question remains, why is part throttle off so much? Somewhere the computer has to account for the fact that my compression, cam timing, and exhaust flow are different from stock.
<strong>Use one of the various injector spreadsheet's to set the proper injector constants
(I have on at http://www.speeddemonmotorsports.com...ectorscale.xls
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">That's what I used. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> Look at the math for SVO 30s using FP = 39 assumption. 1.37 - 1.39 adjustment. I went with 1.39 since I was rich accross the board.
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">
You really shouldn't have to change the shape of the MAF transfer function to much - I would try and see if you can scale by a single factor so your l-trims are from -2 to -6 or so.
To cure your WOT worries use the PE vs RPM
Chris </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You're right, I could do that but I doubt the MAF is off that much, especially since it is descreened which if anything would lean it out just a tad. To me, the question remains, why is part throttle off so much? Somewhere the computer has to account for the fact that my compression, cam timing, and exhaust flow are different from stock.
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Re: Explain the Volumetric Efficency Table Right now the injector rate is fairly linear with a slight upward slope (using graph view). If I were to eliminate the slope by raising the lower MAP values that would probably reduce my LTRIMs and not mess up WOT.
Interesting to observe that the maximum MAP for injector scaling was 80, yet I've seen 105 or 110 in other tables (VE & FA Multiplier) and my ATAP values have approached 100 at WOT. Any thoughts on what the difference is?
Interesting to observe that the maximum MAP for injector scaling was 80, yet I've seen 105 or 110 in other tables (VE & FA Multiplier) and my ATAP values have approached 100 at WOT. Any thoughts on what the difference is?
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Re: Explain the Volumetric Efficency Table The injector table isn't scaled vs. MAP, it is scaled vs. Manifold vacuum, which is Baro - MAP.
(on average around 100 - MAP).
edit: as for not tweaking the MAF tables - once you change anything from stock the MAF tables becomes wrong - lid, K&N, etc. - the entire intake path effects that MAF calibration. I have seen nothing but lid's require a 4% increase in airflow to keep l-trims in line. Same with de-screening it, etc. This doesn't mean you are flowing 4% more air - rather the MAF calibration is now off. (though you are flowing more air - to what extent I don't know).
I wouldn't be afraid to alter the MAF table - if you find yourself deviating more than 10-12% from stock (without a ported MAF) then I might worry.
Chris
<small>[ April 15, 2002, 02:29 PM: Message edited by: ChrisB ]</small>
(on average around 100 - MAP).
edit: as for not tweaking the MAF tables - once you change anything from stock the MAF tables becomes wrong - lid, K&N, etc. - the entire intake path effects that MAF calibration. I have seen nothing but lid's require a 4% increase in airflow to keep l-trims in line. Same with de-screening it, etc. This doesn't mean you are flowing 4% more air - rather the MAF calibration is now off. (though you are flowing more air - to what extent I don't know).
I wouldn't be afraid to alter the MAF table - if you find yourself deviating more than 10-12% from stock (without a ported MAF) then I might worry.
Chris
<small>[ April 15, 2002, 02:29 PM: Message edited by: ChrisB ]</small>
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Re: Explain the Volumetric Efficency Table </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Ragtop 99:
<strong>You're right, I could do that but I doubt the MAF is off that much, especially since it is descreened which if anything would lean it out just a tad. To me, the question remains, why is part throttle off so much? Somewhere the computer has to account for the fact that my compression, cam timing, and exhaust flow are different from stock.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I agree there should be a way to account for these changes, and VE looks like it should be the place, but why are we assuming that an appropriate tuneable parameter (set) exists? It would be great if GM gave us that but I'm not so sure they did. It could just as easily be in the code segment.
My preference is to leave the MAF table alone and handle this via injector scaling. I think of that as two-part cal thing, one a coarse grain cal that characterizes the injector (e.g. scaled for 30# SVOs) and another a fine grain cal for matching the injector to the rest of the system (i.e. adjusting LTFT.) It's kind of a kludge but at least it's a global way to address fuel delivery issues and only fuel delivery issues, something not true with MAF table tinkering.
<strong>You're right, I could do that but I doubt the MAF is off that much, especially since it is descreened which if anything would lean it out just a tad. To me, the question remains, why is part throttle off so much? Somewhere the computer has to account for the fact that my compression, cam timing, and exhaust flow are different from stock.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I agree there should be a way to account for these changes, and VE looks like it should be the place, but why are we assuming that an appropriate tuneable parameter (set) exists? It would be great if GM gave us that but I'm not so sure they did. It could just as easily be in the code segment.
My preference is to leave the MAF table alone and handle this via injector scaling. I think of that as two-part cal thing, one a coarse grain cal that characterizes the injector (e.g. scaled for 30# SVOs) and another a fine grain cal for matching the injector to the rest of the system (i.e. adjusting LTFT.) It's kind of a kludge but at least it's a global way to address fuel delivery issues and only fuel delivery issues, something not true with MAF table tinkering.
Re: Explain the Volumetric Efficency Table Just and FYI, Steve Cole messes with the VE table in his editing. I have a copy of a .ls1 flashfile for a C5 MN6 he worked on.
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Re: Explain the Volumetric Efficency Table I still do not believe it has any effect in MAF mode - I have scaled tables as mentioned above and after days not noticed any difference in stft/ltft (130% increase).
Now if your MAF dies/fues blows, etc. then the VE tables will become operational - and in that instance it might be worthwile to have them scaled.
The formula Ragtop99 posted above is from my LT1 Edit FAQ - you can use that formula to work backwards - values are not specific to the LT1. You will just have to assume a value for Water Vapor pressure, but the rest can be logged. If you want to profile your VE table that is the best way to do it.
Chris
Now if your MAF dies/fues blows, etc. then the VE tables will become operational - and in that instance it might be worthwile to have them scaled.
The formula Ragtop99 posted above is from my LT1 Edit FAQ - you can use that formula to work backwards - values are not specific to the LT1. You will just have to assume a value for Water Vapor pressure, but the rest can be logged. If you want to profile your VE table that is the best way to do it.
Chris
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Re: Explain the Volumetric Efficency Table </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by ChrisB:
<strong>I still do not believe it has any effect in MAF mode - I have scaled tables as mentioned above and after days not noticed any difference in stft/ltft (130% increase).
Chris</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Chris: Was this experiment on an LS1 or LT1?
<strong>I still do not believe it has any effect in MAF mode - I have scaled tables as mentioned above and after days not noticed any difference in stft/ltft (130% increase).
Chris</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Chris: Was this experiment on an LS1 or LT1?
Re: Explain the Volumetric Efficency Table I was saying VE is useful or not just stating that a certain tuner messes with it. But I again concur with ChrisB's data. I was just throwing in different views <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
