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?

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

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?

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.

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.

Well I dunno what you call extreme... My last time at the track was 10.14 @ 136mph...

So you tell me :D

ANyways so your saying that the VE Tables ARE Still used but they are used WITH the PE Tables also at WOT??

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.

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.

WERD, yea I figured it would be more of a challenge but that's all good. I figure with VE Master and my wideband I will be fine...... Hopefully :D

thanks

You guys totally missed what fred was talking about. The VE tables are not fuel values. They're air values.

I think that Fred's explanation was a little more than what the author was looking for, that's all.

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.

But I think its pretty clear that he didn't have the correct idea of the difference between flow measurment and A/F ratio control. I was simply trying to lead him step by step to a clearer understanding.

Sometimes I'm really not sure why I waste my time on some of these questions.... seems people have to complain about everything. :rolleyes:

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.

We can calculate the density of air if we know its pressure (MAP) and its temperature (IAT).

Whats the formula for density?

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.

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. :rolleyes:

Jeez Fred, I don't think anyone complained. All I said was that I think he was looking for a dumbed-down answer and not a full on explanation on how the PCM uses the values in the ve tables to come up with an injector pulsewidth.
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. :)

If all this seems like a lot of work, I have an Excel spreadsheet

That's exactly what I had in mind

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.

Thats me you talking about :)

MS Works comes with a spreadsheet that works just like MS Excell tough. So I am going to do my own from chicken scratch.


** I tried everything and MS wont open the Excell sheet you sent me. Thank you anyways. That was nice of you.

Marvin

Injected SS,
You are unbelievable, Fred, who has forgetten more about LT1's than you'll ever know advises you, and you bad mouth him.

Originally posted by anaik
Injected SS,
You are unbelievable, Fred, who has forgetten more about LT1's than you'll ever know advises you, and you bad mouth him.

WTF? You little a$$hole I never bad mouthed him :mad: He just didn't answer my question like I needed it answered like TriPinTaZ and DanK answered it! Nothing wrong with that.. Fred's answer was fine. We all respect his knowledge, sometimes he just get's carried away that's all.. Not like we hate him or bad mouth him for it...

Your obviously just trying to nut swing :rolleyes: I respect Fred and what he has to say.. He and only a handful of other people are the only people that I will even consider taking advice from on here...

As far as "knows more about LT1's than I will ever know" :rolleyes: What an ignorant statment. You don't know me. When you start pulling times like MINE (http://members.aol.com/injektedss/timeslip/timeslip.html) then maybe I will take your words into consideration... Cause I obviously must know SOMETHING :)

Until then keep being the little bitch a$$ nutswinging troll that you are :cool:

It seems to me that insults don't contribute to a useful discussion. Can't we all get along?

Rich Krause

Originally posted by rskrause
It seems to me that insults don't contribute to a useful discussion. Can't we all get along?

Rich Krause

I agree Rich but hey he had no reason to go off like that :mad: Im not gonna sit and listen to some little nut swinger try to talk crap to me like that. Always some little troll that's gotta say something ignorant :rolleyes:

This whole thread is just another example of the reason I'm about to leave this board, and limit my posts to Advanced Tech. As a minimum, there are people whose posts I totally ignore, because it seems like no matter how hard you try to help them, they find fault with it.

Injuneer.....I have a question! :)

I'm trying to follow your first reply to this post... one out of the only two or three that was useful too, BTW...

You said to divide the displacement (in ft^3) of the engine by 2, and multiply that by the RPM, and this will give you CFM.

Writing this out on paper, I have

ft^3 x rev = ft^3 x rev
2........min..........2 x min

(Excuse all those "....."'s ... I needed that so the fractions would line up.)
What am I missing here?


I figured it out.... i forgot another part, theres 1 intake stroke for every 2 rev's of the crank. So, you multiply the above equation by 1/2, which equals the formula already stated... I did it again, I answered my own question... shoulda thought it out more sorry for thinking out loud.

I would like to see that spread sheet if you get a chance.

Thanks,
Dustin
dkeers@iupui.edu

because it seems like no matter how hard you try to help them, they find fault with it.

I know exactly what you mean Fred. Picture this... Me Red Camaro z28 black top driving way out there in the sticks..... way way in the South. I spot a white Silverado stranded on the side of the road... I pull up to help... is being driven by a White Man with shaven Head and has the confederate flag wraped on his cabin seat...I notice his bumper sticker "the south will rise". Me hispanic with spanish accent and light brown complexion. I asked him if he needs a ride to the nearest town. He looks at me Like I am out of my freaggin mind and then He replys "why dont you mind your F&%$ng bussiness! wet back!" with a deep, corn-fed overgrown Alabama Accent. Being the mentally disturbed person that I am I look at him in the eye (at a safe distance) and then while I rub my crotch I say "Boy do I like your women soo much better" with the nasties Mexican accent I could imitate... Man the dude ran to pull something out of his truck, I flew out to my car and I was out of there faster than hungry Hick bites on a boiled racoon for dinner... (oops I shoulndt have said that). But honest I was so sore for gettin insulted while all I wanted was to help a fellow human being in distress.

I am serious, I know what Fred is saying.

Marvin

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.

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.

Does this apply to OBD I LT1, as well as OBD II LT1 and LS1?

i know it works on OBD2 LT1, cant say for any other