VE Tables???
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VE Tables???
Im going to give speed density a try because i wanna bypass the MAF and have some more versality on tuning...
Im wondering WHY the VE Tables go soo high, like RPM wise since I would think that if I were higher than say 4k rpms more than likely my tps % would be within the values for PE Mode so why would having #'s in the VE Tables that high necessary?
Im wondering WHY the VE Tables go soo high, like RPM wise since I would think that if I were higher than say 4k rpms more than likely my tps % would be within the values for PE Mode so why would having #'s in the VE Tables that high necessary?
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Joined: Nov 1998
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From: Hell was full so they sent me to NJ
Your mixing up the air flow measurements with the A/F ratio control.
Speed-density is simply a method that uses a formula to calculate MASS air flow into the engine, rather than using a MAF sensor, which can measure MASS air flow directly. This has nothing to do with whether the PCM control is in open loop, closed loop, PE mode, etc. That is what the PCM does with the MASS air measurement AFTER it has it.
To calculate mass air flow, you multiply displacement/2 X rpm. If you started with cubic feet displacement, that gives you cubic feet of air per minute. But, the cylinder does not necessarily fill completely with air. In a stock setup, it might fill only to the 80% level, because of breathing limitations. That would represent a volumetric effciency (VE) of 80%.
So now we multiply:
displacement/2 X RPM X VE = CFM of air flowing into the engine.
But, we need to know the weight (MASS) of the air, or pounds or air, so that we can add the correct mass of fuel. To convert CFM to pound/minute, we need to know the density of the air.... expressed in pounds/cubic feet. We can calculate the density of air if we know its pressure (MAP) and its temperature (IAT). So, now we have:
displacement/2 X RPM X VE X density = pounds/minute of air
And, only then does the PCM pick a "target" A/F ratio.... 14.7:1 on closed loop, a variable number in PE mode.... and multiply the air mass flow times the A/F ratio to get the pounds/minute of fuel. It then uses the injector constant to set the pulse width.
displacement/2 X RPM X VE X density X A/Fratio = pounds/minute of fuel
Speed-density is simply a method that uses a formula to calculate MASS air flow into the engine, rather than using a MAF sensor, which can measure MASS air flow directly. This has nothing to do with whether the PCM control is in open loop, closed loop, PE mode, etc. That is what the PCM does with the MASS air measurement AFTER it has it.
To calculate mass air flow, you multiply displacement/2 X rpm. If you started with cubic feet displacement, that gives you cubic feet of air per minute. But, the cylinder does not necessarily fill completely with air. In a stock setup, it might fill only to the 80% level, because of breathing limitations. That would represent a volumetric effciency (VE) of 80%.
So now we multiply:
displacement/2 X RPM X VE = CFM of air flowing into the engine.
But, we need to know the weight (MASS) of the air, or pounds or air, so that we can add the correct mass of fuel. To convert CFM to pound/minute, we need to know the density of the air.... expressed in pounds/cubic feet. We can calculate the density of air if we know its pressure (MAP) and its temperature (IAT). So, now we have:
displacement/2 X RPM X VE X density = pounds/minute of air
And, only then does the PCM pick a "target" A/F ratio.... 14.7:1 on closed loop, a variable number in PE mode.... and multiply the air mass flow times the A/F ratio to get the pounds/minute of fuel. It then uses the injector constant to set the pulse width.
displacement/2 X RPM X VE X density X A/Fratio = pounds/minute of fuel
Thread Starter
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What? No Im aware of how speed density works. Speed Density DOES NOT utilize the MAF Sensor. So basically all of the part throttle tuning is done through the VE Tables and then all the WOT tuning is done through the PE Tables... Considering you still have the car running in CLOSED LOOP.
So my question was "WHY do the Ve Tables go so high" because if you think about it, if I were at 5k RPMS and at a map of 80, then I obviously have the car floored, OR at least within a values that is in the TPS % for WOT Table to be considered PE Mode, so then the computer would be using the PE Tables for the WOT fueling and NOT the VE Tables... So WHY are they that high then?
So my question was "WHY do the Ve Tables go so high" because if you think about it, if I were at 5k RPMS and at a map of 80, then I obviously have the car floored, OR at least within a values that is in the TPS % for WOT Table to be considered PE Mode, so then the computer would be using the PE Tables for the WOT fueling and NOT the VE Tables... So WHY are they that high then?
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THE VE tables are still used in PE mode when at WOT. The only thing the PE tables do is add X amount of fuel ONTOP of what the VE tables are at. In speed density mode your VE TABLE is your CORE fueling table, and the 02's do corrections.
If you are not running an extreme combination and the MAF is not hurting flow, deleting your MAF is probably not a good idea. Your taking another tool away from your PCM for fueling calculations.
If you are not running an extreme combination and the MAF is not hurting flow, deleting your MAF is probably not a good idea. Your taking another tool away from your PCM for fueling calculations.
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Originally posted by TriPinTaZ
THE VE tables are still used in PE mode when at WOT. The only thing the PE tables do is add X amount of fuel ONTOP of what the VE tables are at. In speed density mode your VE TABLE is your CORE fueling table, and the 02's do corrections.
If you are not running an extreme combination and the MAF is not hurting flow, deleting your MAF is probably not a good idea. Your taking another tool away from your PCM for fueling calculations.
THE VE tables are still used in PE mode when at WOT. The only thing the PE tables do is add X amount of fuel ONTOP of what the VE tables are at. In speed density mode your VE TABLE is your CORE fueling table, and the 02's do corrections.
If you are not running an extreme combination and the MAF is not hurting flow, deleting your MAF is probably not a good idea. Your taking another tool away from your PCM for fueling calculations.
So you tell me
ANyways so your saying that the VE Tables ARE Still used but they are used WITH the PE Tables also at WOT??
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YES, at WOT the VE tables AND the PE tables are both used.
if your MAF is disabled then your cars PCM relies directly on your VE TABLES for fuel. When the car enters PE mode at WOT the number in the PE table is the % fuel increase/decrease from what the VE table says.
Example your VE tables reads 94.3 @ 6000 RPMs @ 100 KPA, we will call this amount of fuel "X"
Now in your PE table, lets say at 6000 RPMs it reads 13.5. This means that at WOT when engine is at 6000 RPMs the PCM will give it X fuel PLUS 13.5 % increase. ( unless you ahve a negative # in the PE tables, in that case it will subtract fuel based on the VE table map)
In speed density mode the PCM will not ignore VE tables at WOT, it just adds/subtracts the % of fuel that is in the PE table FROM the VE table.
The only issue with Speed Density is tuning it for part throttle driving, it takes alot of time and effort to get it right and when the weather changes ( humidity/temp ) the PCM will not compensate like a car with a MAF would. So you might find you need to make a few different tunes when you go to the track based on the weather to get the most out of your car.
if your MAF is disabled then your cars PCM relies directly on your VE TABLES for fuel. When the car enters PE mode at WOT the number in the PE table is the % fuel increase/decrease from what the VE table says.
Example your VE tables reads 94.3 @ 6000 RPMs @ 100 KPA, we will call this amount of fuel "X"
Now in your PE table, lets say at 6000 RPMs it reads 13.5. This means that at WOT when engine is at 6000 RPMs the PCM will give it X fuel PLUS 13.5 % increase. ( unless you ahve a negative # in the PE tables, in that case it will subtract fuel based on the VE table map)
In speed density mode the PCM will not ignore VE tables at WOT, it just adds/subtracts the % of fuel that is in the PE table FROM the VE table.
The only issue with Speed Density is tuning it for part throttle driving, it takes alot of time and effort to get it right and when the weather changes ( humidity/temp ) the PCM will not compensate like a car with a MAF would. So you might find you need to make a few different tunes when you go to the track based on the weather to get the most out of your car.
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Originally posted by TriPinTaZ
YES, at WOT the VE tables AND the PE tables are both used.
if your MAF is disabled then your cars PCM relies directly on your VE TABLES for fuel. When the car enters PE mode at WOT the number in the PE table is the % fuel increase/decrease from what the VE table says.
Example your VE tables reads 94.3 @ 6000 RPMs @ 100 KPA, we will call this amount of fuel "X"
Now in your PE table, lets say at 6000 RPMs it reads 13.5. This means that at WOT when engine is at 6000 RPMs the PCM will give it X fuel PLUS 13.5 % increase. ( unless you ahve a negative # in the PE tables, in that case it will subtract fuel based on the VE table map)
In speed density mode the PCM will not ignore VE tables at WOT, it just adds/subtracts the % of fuel that is in the PE table FROM the VE table.
The only issue with Speed Density is tuning it for part throttle driving, it takes alot of time and effort to get it right and when the weather changes ( humidity/temp ) the PCM will not compensate like a car with a MAF would. So you might find you need to make a few different tunes when you go to the track based on the weather to get the most out of your car.
YES, at WOT the VE tables AND the PE tables are both used.
if your MAF is disabled then your cars PCM relies directly on your VE TABLES for fuel. When the car enters PE mode at WOT the number in the PE table is the % fuel increase/decrease from what the VE table says.
Example your VE tables reads 94.3 @ 6000 RPMs @ 100 KPA, we will call this amount of fuel "X"
Now in your PE table, lets say at 6000 RPMs it reads 13.5. This means that at WOT when engine is at 6000 RPMs the PCM will give it X fuel PLUS 13.5 % increase. ( unless you ahve a negative # in the PE tables, in that case it will subtract fuel based on the VE table map)
In speed density mode the PCM will not ignore VE tables at WOT, it just adds/subtracts the % of fuel that is in the PE table FROM the VE table.
The only issue with Speed Density is tuning it for part throttle driving, it takes alot of time and effort to get it right and when the weather changes ( humidity/temp ) the PCM will not compensate like a car with a MAF would. So you might find you need to make a few different tunes when you go to the track based on the weather to get the most out of your car.
thanks
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From: Hell was full so they sent me to NJ
Originally posted by Dan K
I think that Fred's explanation was a little more than what the author was looking for, that's all.
I think that Fred's explanation was a little more than what the author was looking for, that's all.
Sometimes I'm really not sure why I waste my time on some of these questions.... seems people have to complain about everything.
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Joined: Dec 2002
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YES VE tables refer to the efficiency of air the engine is using for combustion. so a higher value would mean the PCM adds more fuel because its efficiency is higher. Sorry to mislead, but it was the simplest way to expalin it.
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Joined: Nov 1998
Posts: 71,110
From: Hell was full so they sent me to NJ
You can use the "perfect gas law" and calculate it from scratch, but the easiest way is to calculate it from a know density.
The density of air is 0.0808 pounds/cubic foot at 32degF (492degR) and 29.98"Hg. To calculate the density, in pounds/cubic foot at some other temperature (IAT) and pressure (MAP), you need to use ratios.
First, both the temperature and pressure must be in "absolute" units. Manifold absolute pressure is already in absolute units. Temperature in degrees-F is not. To get an absolute temperature, you add 460 to the degrees-F, and that gives you degrees-R (Rankine, a reference to absolute zero).
To get the density at 60degF (460 + 60 = 520degR)and 28.0"Hg, for example:
0.0808 X (492/IAT) X (MAP/29.98) =
0.0808 X (492/520) X (28.0/29.98) =
0.0808 X 0.9462) X (0.9340) = 0.0714 pounds/cubic foot
If all this seems like a lot of work, I have an Excel spreadsheet that will give you actual air flow, in pounds/minute or grams/second, based on inputs for displacement, rpm, VE, IAT and MAP. I can send a copy to anyone who wants it. I understand from someone who tried to open it with MS Works rather than an actual copy of Excel that the password protection seems to prevent it from opening.
The density of air is 0.0808 pounds/cubic foot at 32degF (492degR) and 29.98"Hg. To calculate the density, in pounds/cubic foot at some other temperature (IAT) and pressure (MAP), you need to use ratios.
First, both the temperature and pressure must be in "absolute" units. Manifold absolute pressure is already in absolute units. Temperature in degrees-F is not. To get an absolute temperature, you add 460 to the degrees-F, and that gives you degrees-R (Rankine, a reference to absolute zero).
To get the density at 60degF (460 + 60 = 520degR)and 28.0"Hg, for example:
0.0808 X (492/IAT) X (MAP/29.98) =
0.0808 X (492/520) X (28.0/29.98) =
0.0808 X 0.9462) X (0.9340) = 0.0714 pounds/cubic foot
If all this seems like a lot of work, I have an Excel spreadsheet that will give you actual air flow, in pounds/minute or grams/second, based on inputs for displacement, rpm, VE, IAT and MAP. I can send a copy to anyone who wants it. I understand from someone who tried to open it with MS Works rather than an actual copy of Excel that the password protection seems to prevent it from opening.
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Joined: Jul 2001
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From: so close I can taste it...
Originally posted by Injuneer
Sometimes I'm really not sure why I waste my time on some of these questions.... seems people have to complain about everything.
Sometimes I'm really not sure why I waste my time on some of these questions.... seems people have to complain about everything.
InjectedSS was under the assumption that once in pe mode the only values that were used to determine fueling were the pe tables...but TriPinTaZ fixed him.
Don't take everything to heart...without you some of us would be lost. We always have your knowledge to fall back on.
