Fuel Trim & VE
09-21-2003, 10:52 PM
#81
Re: Fuel Trim & VE
The formula I posted should correspond to NoGo's with the included addition of temperature as a factor. That is the one that seemed to me also to best fit the ls1's stock curve. If you want to check it out vs. barometric pressure just replace the MAP term with barometric pressure (in kPa)
The point you are missing I think is that the table works (and is the most noticeable) at part throttle also - and here you have a huge restriction due to the throttle blade itself. Basically when you use manifold pressure as the reference for VE you are measuring puping losses from the pressure sensor to the cylinder - if you use atmospheric as the reference you are measuring pumping losses from the atmosphere to the cylinders.
Re: needing the VE tables - if you use a formula you effectively have an infinitely granular table - you don't have to interpolate for points that are inbetween your lookup points as the formula gives you the exact answer - so the formula based approach in that sense would definitely be superior.
I honestly don't know, but I don't think it's to prevent problems with bad sensors, etc. - the MAF is going to be the primary factor in the VE formulae as well as in stock fueling - if either goes dead then the car is going to run like ****. Now if you have a separate VE lookup table you can reference that if the MAF dies - which is an advantage. I think any harmonics introduced by the continues sensor inputs would be resolved by "tweaking" the model itself. Just add a dampening factor if you need it.
The other question still remains though - what exactly do we need the VE table for - the MAF tells us exactly how much air is inducted - so we now how much air is in each cylinder (the basis for the top of the VE equation) - if you know the mass of the air in the cylinder, your desired fuel ratio, and injector flow rate you know exactly how long to pulse the injector to get that fuel in there.
So what exactly "real world" phenomenon is the VE table compensating/modifying for? Definitely not VE in a classical sense, as the MAF makes that uneccecary. Again, the only thing I can come up with is charge quality - as we are shooting for a perfectly atomized yyy A/F ratio, but due to this being the real world that doesn't always happen.
For this to work though the VE would have to be proportional to charge quality in some sense - well, in a way that required reduced fueling as VE goes down, and increased as VE goes up (as a bpw modifier).
Or it could be some other factor I am totally missing - I am just trying to figure out now the reason for inclusion of the VE factor in MAF based fueling?
The point you are missing I think is that the table works (and is the most noticeable) at part throttle also - and here you have a huge restriction due to the throttle blade itself. Basically when you use manifold pressure as the reference for VE you are measuring puping losses from the pressure sensor to the cylinder - if you use atmospheric as the reference you are measuring pumping losses from the atmosphere to the cylinders.
Re: needing the VE tables - if you use a formula you effectively have an infinitely granular table - you don't have to interpolate for points that are inbetween your lookup points as the formula gives you the exact answer - so the formula based approach in that sense would definitely be superior.
I honestly don't know, but I don't think it's to prevent problems with bad sensors, etc. - the MAF is going to be the primary factor in the VE formulae as well as in stock fueling - if either goes dead then the car is going to run like ****. Now if you have a separate VE lookup table you can reference that if the MAF dies - which is an advantage. I think any harmonics introduced by the continues sensor inputs would be resolved by "tweaking" the model itself. Just add a dampening factor if you need it.
The other question still remains though - what exactly do we need the VE table for - the MAF tells us exactly how much air is inducted - so we now how much air is in each cylinder (the basis for the top of the VE equation) - if you know the mass of the air in the cylinder, your desired fuel ratio, and injector flow rate you know exactly how long to pulse the injector to get that fuel in there.
So what exactly "real world" phenomenon is the VE table compensating/modifying for? Definitely not VE in a classical sense, as the MAF makes that uneccecary. Again, the only thing I can come up with is charge quality - as we are shooting for a perfectly atomized yyy A/F ratio, but due to this being the real world that doesn't always happen.
For this to work though the VE would have to be proportional to charge quality in some sense - well, in a way that required reduced fueling as VE goes down, and increased as VE goes up (as a bpw modifier).
Or it could be some other factor I am totally missing - I am just trying to figure out now the reason for inclusion of the VE factor in MAF based fueling?
For this to work though the VE would have to be proportional to charge quality in some sense - well, in a way that required reduced fueling as VE goes down, and increased as VE goes up (as a bpw modifier).
* This is what I've read was the purpose of the VE table - "VE is used in the Base Injector Pulsewidth Equation".
* I have only learned LS1 tuning- no LT1 Tuning, so I'm not confusing the Two.( Camaroholic's excellent advice since I don't have an interest in LT1s).I thought I read this in the Fuel Injection Book by Probst but I'm unable to find the quote!
* Anyway, used as you describe, it's a Ve table whether used for the entire engine or unit cylinder filling - Right??? So that must be it's purpose - because this sure as hell isn't a perfect world. Now I get it!!
joel
09-21-2003, 10:55 PM
#82
Re: Fuel Trim & VE Actually I tried to make the formula simpler - the displacement here should be for that of the entire engine.
Try
{SAE.MAF.gps} * (SAE.IAT.C + 273.15) / (347 * {SAE.RPM} * {SAE.MAP.kPa}) * 212544
all you need is that one set of parentheses
joel
09-21-2003, 11:20 PM
#83
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Re: Fuel Trim & VE The 212544 value there includes the constant, "R" with in^3 as a unit. I don't think it ever should have been in terms of cubic ft (not sure where that came from).
Re: the VE table - even if we know it is a multiplier we still don't know the rational behind it - e.g., what part of the IC engine is it modeling (since I still don't see the rational for needing VE information when you have MAF information - which if you look at SD algorithms all the VE is used for is to give us the information that the MAF measures directly). Not that this prevents us from using it, I am just curious as to what it is actually doing there
Re: the VE table - even if we know it is a multiplier we still don't know the rational behind it - e.g., what part of the IC engine is it modeling (since I still don't see the rational for needing VE information when you have MAF information - which if you look at SD algorithms all the VE is used for is to give us the information that the MAF measures directly). Not that this prevents us from using it, I am just curious as to what it is actually doing there
09-22-2003, 09:11 AM
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Re: Fuel Trim & VE The lag idea is definitely a good possibility - if that is the case though I would think we would need an attack and decay rate that applies to the VE multiplier and is scaled vs deltaTPS or something like that.
I tried to look at some of the log files I had to determine if there was a correlation between the two, but didn't have enough data points really.
If it is to correct for lag then changing the position of the MAF would have a big difference on operation - are any of the FI kits setting up the MAF to run on the intake side?
VT2: I belive NoGo wrote about that a bit earlier - essentially you would use the formula's posted above to determine your VE, then enter that into the table. I would still be a bit dubious as to the benefit of that, unless you have a pcm with multi-bar capability or packaging demands it.
I tried to look at some of the log files I had to determine if there was a correlation between the two, but didn't have enough data points really.
If it is to correct for lag then changing the position of the MAF would have a big difference on operation - are any of the FI kits setting up the MAF to run on the intake side?
VT2: I belive NoGo wrote about that a bit earlier - essentially you would use the formula's posted above to determine your VE, then enter that into the table. I would still be a bit dubious as to the benefit of that, unless you have a pcm with multi-bar capability or packaging demands it.
09-22-2003, 01:24 PM
#87
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Re: Fuel Trim & VE I read a while back in the ls1edit mailing list that someone posted a quote from a gm manual that said the maf is inaccurate at large throttle changes, and the pcm uses alternate fueling. But as to why the ve is used at cruising, I don't know.
09-23-2003, 12:29 PM
#88
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Re: Fuel Trim & VE Try this out. Our cars are sold and driven in every weather climate. The tunes are the same regardless. Most of the functions in the VE formula are effected by weather. Perhaps there is a weather related function for VE. If so, shouldn't we only change the VE table if we have changed something like the MAF or added a blower, etc?
09-24-2003, 07:30 PM
#89
Re: Fuel Trim & VE
Try this out. Our cars are sold and driven in every weather climate. The tunes are the same regardless. Most of the functions in the VE formula are effected by weather. Perhaps there is a weather related function for VE. If so, shouldn't we only change the VE table if we have changed something like the MAF or added a blower, etc?
Weather only changes density and temp - which correlates with density ( I think it's from Boyle's gas laws, PV=nRT....it's been 30 years since I was in school!) MAF and MAP pretty much take care of this. In theory shouldn't VE be a constant at a given RPM and MAP? VE is independent of Temp and Pressure ...we're just using them to experimentally determine the actual values(constants).
I think the VE table is for Volumetric Efficiency. What I mean is if we could go by the MAF then VE equals 1 and we don't need a table. It's common knowledge that all engines have varying efficiencies at different RPMs and MAPs- especially due to cam profiles (overlap) etc.
*
For example-I'm still trying to tune my cam currently. Now, it has a lot of overlap. At around 2000 RPM and MAP=45-55 it was running PIG (10.8) RICH. It then would detonate ->KR and fall on it's face. Funny thing was the Inj.PW was NOT real high so I assumed it must be due to inefficiencies in the system. By this I mean too much fuel at that RPM and Map- which was accurate and efficient when the motor was stock-but now it's too much fuel. So I went to the VE table and slightly reduced it in this area. The Inj PW narrowed and the AFR went to around 12.3. Still too rich but I'm not getting Knock Retard. I reduced the VE table to reflect the reduced VE of my motor at the above RPM and MAP.
*
My point is the 106 lsa of my cam is very inefficient at lower RPMs and the MAF shows
reasonable gm/cyl values at the stated MAP and RPM. But not all the Mass of air is going to combustion - some is lost due to reversion, some is blowby etc. If all I had was MAF what would I adjust??
I think I would have to adjust Fueling at a given RPM and MAP.......that's a VE table.
Sorry, for the mini book . Does this make sense to you guys??
09-24-2003, 11:38 PM
#90
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Re: Fuel Trim & VE I was thinking about Chris B's question regarding the reason for having VE. Your likely right that the values need to be adjusted for the "new" engine. Just look at the LS6 and LS1 VE tables. They're different because there are differences in the engines. So I think your right, the table has use for adjusting to many changes. I was thinking more in terms of what it might doing for a stock engine, which was not meant to be modified. Since Map is a function in VE and temps do change the density of the air injested, it just seems like it is a factor in adjusting for weather.
Team ZR1 posted on Edit that his Ltrims did not change with changes in the VE tables. I'm not argueing the point, but mine did change when I put the ZO6 values in mine. Maybe something else was involved. I also had to richen my AFR. This seems more clear, since those values were under 1 at high RPMs and all the values have been raised by .04 to maintain 13.1.
I also wonder about the effect of having installed the Z06 VE values while keeping the LS1 MAF values?
Team ZR1 posted on Edit that his Ltrims did not change with changes in the VE tables. I'm not argueing the point, but mine did change when I put the ZO6 values in mine. Maybe something else was involved. I also had to richen my AFR. This seems more clear, since those values were under 1 at high RPMs and all the values have been raised by .04 to maintain 13.1.
I also wonder about the effect of having installed the Z06 VE values while keeping the LS1 MAF values?
09-25-2003, 01:22 PM
#91
Re: Fuel Trim & VE
I was thinking about Chris B's question regarding the reason for having VE. Your likely right that the values need to be adjusted for the "new" engine. Just look at the LS6 and LS1 VE tables. They're different because there are differences in the engines. So I think your right, the table has use for adjusting to many changes. I was thinking more in terms of what it might doing for a stock engine, which was not meant to be modified.
>>>>>Since Map is a function in VE and temps do change the density of the air injested, it just seems like it is a factor in adjusting for weather.
Our cars adjust for Barometric pressure ( I believe at start up) and MAP is an Absolute value.
>>>>>Team ZR1 posted on Edit that his Ltrims did not change with changes in the VE tables. I guess he didn't make enough of a change or didn't drive long enough? I'm not argueing the point, but mine did change when I put the ZO6 values in mine. Maybe something else was involved. I also had to richen my AFR. This seems more clear, since those values were under 1 at high RPMs and all the values have been raised by .04 to maintain 13.1.
>>>>>>I also wonder about the effect of having installed the Z06 VE values while keeping the LS1 MAF values?Interesting question.Since it's properly scaled I would think you're ok maybe one of the Gurus can Answer this. joel
>>>>>Since Map is a function in VE and temps do change the density of the air injested, it just seems like it is a factor in adjusting for weather.
Our cars adjust for Barometric pressure ( I believe at start up) and MAP is an Absolute value.
>>>>>Team ZR1 posted on Edit that his Ltrims did not change with changes in the VE tables. I guess he didn't make enough of a change or didn't drive long enough? I'm not argueing the point, but mine did change when I put the ZO6 values in mine. Maybe something else was involved. I also had to richen my AFR. This seems more clear, since those values were under 1 at high RPMs and all the values have been raised by .04 to maintain 13.1.
>>>>>>I also wonder about the effect of having installed the Z06 VE values while keeping the LS1 MAF values?Interesting question.Since it's properly scaled I would think you're ok maybe one of the Gurus can Answer this. joel
09-28-2003, 07:18 AM
#92
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Re: Fuel Trim & VE speed density tables and VE tables are in there in case of the maf fails. they are not tuned well as they are.
big cams effect maf input, it is necessary to delete the maf and spend a lot of time to tune the speed density tables. big cams will then run as smooth as a maf car with a stock or very small cam (although with a higher idle speed). SD will be more susceptible to changes in VE than a maf tune will be.
big cams effect maf input, it is necessary to delete the maf and spend a lot of time to tune the speed density tables. big cams will then run as smooth as a maf car with a stock or very small cam (although with a higher idle speed). SD will be more susceptible to changes in VE than a maf tune will be.
10-03-2003, 11:47 AM
#93
Re: Fuel Trim & VE
speed density tables and VE tables are in there in case of the maf fails. they are not tuned well as they are.
big cams effect maf input, it is necessary to delete the maf and spend a lot of time to tune the speed density tables. big cams will then run as smooth as a maf car with a stock or very small cam (although with a higher idle speed). SD will be more susceptible to changes in VE than a maf tune will be.
big cams effect maf input, it is necessary to delete the maf and spend a lot of time to tune the speed density tables. big cams will then run as smooth as a maf car with a stock or very small cam (although with a higher idle speed). SD will be more susceptible to changes in VE than a maf tune will be.
joel
10-05-2003, 08:41 PM
#94
Re: Fuel Trim & VE
speed density tables and VE tables are in there in case of the maf fails. they are not tuned well as they are.
big cams effect maf input, it is necessary to delete the maf and spend a lot of time to tune the speed density tables. big cams will then run as smooth as a maf car with a stock or very small cam (although with a higher idle speed). SD will be more susceptible to changes in VE than a maf tune will be.
big cams effect maf input, it is necessary to delete the maf and spend a lot of time to tune the speed density tables. big cams will then run as smooth as a maf car with a stock or very small cam (although with a higher idle speed). SD will be more susceptible to changes in VE than a maf tune will be.
joel
11-13-2003, 09:04 PM
#97
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Originally Posted by vt2vx
speed density tables and VE tables are in there in case of the maf fails. they are not tuned well as they are....
11-17-2003, 12:42 PM
#98
Originally Posted by TooManyIDs
I did a quick scan on a 2000 Vette Coupe (LS1), and two 2002 Z06's. All cold & warm starts were in open loop mode. My understanding is that the VE tables will be used in that case.
joel
