DAN K

- when you chage the VE table lower you are telling the PCM that the engine is less efficient in complete/efficiant combustion.

@ 75 KPA @ 3000 RPMs the VE table reads 87.5 on my tune. This simply means, at that given operating parameters 87.5% of the air entering the engine is being efficiently combusted. Therefor the PC adds X amount of fuel. If you lower this number the PCM will say there is less air being efficiently combusted, so the PCM adds less fuel. Then in closed loop the PCM use the numbers in teh VE tables as a base reference and uses the MAF and O2s to correct A/F.

So changing the MAF sensor tables changes the way the MAF compensates for correct A/F with the 02s. Basically this will work fine. But becomes very innacurate when the engine becomes heavily modified like mine. And inhibits the PCMs ability to compensate for proper A/F acroos the ENTIRE operating parameters of the engine and not just WOT.


As far as wideband O2, You tune the PE for WOT, from this point you need to work the table smoothly down through the operating range at part throttle and decal. Then it takes time and driving and data logging to tune out any tweaks, such as idle too rich or stumbling. ( timing tables help greatly here too)

Like I stated it takes time , but when done correctly the car runs great. I ahve tuned my cars VE tables atleast 20 times from the Dyno tune. You just keep the 95-100 KPA tables from the dyno and use that as a basis for your tune.

 

TriPinTaz, I'm interested in whole VE table concept and what it does for the engine at part throttle. I've seen a lot of people go back and forth over whether or not they do anything or if they do nothing at all (In my opinion they have to do something, otherwise GM wouldn't have the things in there). Do you have any more information or documents that could help to explain these tables and their effects based on mods better? I've not yet had to use them, but I'd like to be able to utilize every aspect of tuning rather than just the majority of them.

 

I know how the ve tables work and what the values mean. I've done a couple of 93's and they work off of the ve tables, so that's not the issue.
I guess I still don't understand what you're shooting for when tuning the ve tables for anything other than wot? Are you just tuning by what the car feels like or trying to get a certain blm? Part throttle doesn't really need much fueling work as the PCM adjusts via O2 sensor feedback. As long as you're within range, you're fine. Just seems to me that some folks worry a little too much about part throttle fueling and trying to get a 128 blm because they think that any value under this means you're rich and over it means you're lean.
I just don't understand what the advantage of tuning the ve tables is when part throttle fueling is all done by the PCM and when wot can be done through pe tables.
But I'd love to learn.

 

well quite frankly, until you have more experience in the area of VE tuning I dont expect you to understand.

Basically if you get the VE tables right, there is LESS for the PCM to correct. and the cars performance is more consistant during part throttle driving.

 

OUCH That is out of line

TriPinTaZ we are all on here to learn how to tune your cars and help others, tell us help us under stand how the ve tables work and work with the PE tables and the coolant tables, for driving and wot, i would like to know this too.

hey winter is coming i have allot of time to read

 

i didnt mean for it to be so harsh. I thought I explained the VE tables already. VE = Volumetric Efficiency, which in other words is how efficient your engine is at complete combustion of all incoming air. In your PE tables you have the idle cells in the 70's in your VE table. This means that the PCM will refer to these numbers for is base fueling at idle and then use the MAF and O2 feedback to make any compensations for fueling ( If in OPEN LOOP mode it will not use the O2s). the 70's number you have in the VE tables is telling the PCM that at idle the car is approx. using 70% of the incoming air measured by the MAF for efficient/complete cumbustion. So the PCM only adds enough fuel to maintain the A/F ratio based on the info that only 70% of the air will be used for combustion. If you were t change the VE to 100 at idle, the PCM would add more fuel because it thinks 100% of the air going thru the MAF is being efficiently combusted. In this case you would certainly be too rich.

My car has a huge 260/260 @.50 solid roller and my idle VE tables are around 50-60. Because of the large overlap only 50% or so of hte air entering thru my MAF sensor is being combusted at idle.

I do not know how to better expalin this.

Schurters LT1 - After looking at your Tune your VE tables have been modified greatly from a stock tune. You would probably gain better gas mileage abd part throttle driving by enabling closed loop mode and using the WOT table trick i expalined to you in Email. This way the PCM will ignore the O2s at idle. However you may have to lower your idle VE tables a little. But as I also said your Timing tables are way off for 400-4000 RPMs. I cant imagine how your car runs at part throttle.

I sent you a copy of my tune, mine is a closed loop enabled tune sothe VE tables will be a little different then yours.

 

TriPinTaZ i never sent you my tune file i just went back down to the dyno and Spraytheway helped me well tuned my car , i made power but i did it a$$ backwards he fixed it all up i just would like to know how to do all this

 

Sorry wise one.
You can explain what a ve table is all that you want and that you modified the hell out of them because you're car is highly modified, but until you tell us what kind of data you're looking at in order to know what kinds of changes to make to the tables then you aren't helping anyone. Tha'ts all I've been trying to get out of you.
But it doesn't seem like you've answered any of the questions I've asked you...so I'm not going to worry about it anymore.
The pcm can calculate part throttle fueling for me and I'll use my "tricks" of playing with the maf tables and injector constant in order to get the long term fuel trims to an area where the pcm is able to adjust by itself. Then if I can't tune wot with the pe tables I guess I'll just be screwed.

 

I was looking for information as well, not condescending comment about how I don't understand it. I already stated that I don't fully understand it and that I'm looking for information relative to how it works. Like information that involves the modifications themselves and how they make and effect on the engine's VE. Other things such as timing and how it relates would be nice. Since your not interested in helping, I'll look elsewhere. Thanks for being an ***.

 

sorry it was blk95ta who sent me his file, not you.

As far as the rest of you calling me an *** and that you dont understand the effects MODs have on the VE of an engine......Well Like I said, I dont expect you to understand and Im not going to write a book about it. Go learn like I did, hands on, research, and HANDS ON in the dyno room.....and a very knowlegable Engine Builder.

I wasnt trying to be an ***, but since you want me to be one I will.

Buzz Off and keep paying people to make you half assed tunes for your cars

 

The problem Taz is that we appear to be dealing with two different definitions of Volumetric Efficiency (VE)..... the "classical" definition, and yours. Not saying you are wrong, but your definition is not what engine builders traditionally mean when they say VE.

VE is in effect the efficieny of the engine's breathing (not necessarily its combustion)... what is the mass of air actually contained in the cylinder, for purposes of combustion, compared to the theoretical volume of the cylinder. If you rotate a stock LT1 crank 2 times, it "displaces" 350 cubic inches of internal cylinder volume. Theoretically, if you filled the cylinders with 100% of the air mass, calculated at MAP and IAT, that would occupy that volume, your VE would be 100%.

But it doesn't necessarily happen that way. The dynamics of the pulsating air flow, including the results of the cam profile will either limit or enhance air flow. In your typical mass produced stock engine, you might only see 80% of the mass of the air actually filling the cylinders. With a well designed high performance engine, you might see 90-95% VE. With an engine that runs in a narrow range of RPM (e.g. NASCAR), with the ability to "tune" intake and exhaust runner frequencies, you can exceed 100% VE. The pressure in the cylinder is actually above atmospheric pressure because of the wave pulses.

Speed-density relies heavilly on VE. It is very easy to calculate the displaced volume as the engine rotates.... basically displacement X rpm/2 (with appropriate "units", of course). And it is very easy to calculate the density of the air available to fill the cylinders, by using the perfect gas law and the absolute pressure (MAP) in the intake, and the absolute temperature (IAT + 460 in the english system) in the intake.

Now you have displaced volume x density = mass air flow.

But that's at 100% VE. The engine doesn't operate at 100% VE, so the designers put it on an engine dyno, and measure the VE under various operating conditions. Now your equeation, for determining mass flow becomes:

displaced volume X density X VE = actual mass air flow.

The fuel sytem now needs to deliver the correct mass of fuel to match the actual mass air flow.

So.... that explains why you need to know VE, in order to properly tune a speed-density setup. And that's the traditional meaning of VE... the ratio of the actual air flow the the displaced volume.

In theory, a "mass air" setup eliminates all of the above..... it directly measures the mass flow of air at any point in time.... doesn't need to know displacement, rpm, MAP, IAT or VE.

But, if the mass-air system is required to default to speed-density when the mass air measurement is lost, it needs to have the VE table available.

You are apparently bringin up a different concept, which someohow relates to "combustion efficiency". And in all honesty, I can't follow what you are saying.... not to say you are wrong.... only that I can not understand your explanation of VE as it relates to mass air. And I think that is why people are having a hard time understanding you.

Look at what you are saying.... the mass-air sensor makes an air flow measurment at idle, and you call that 100%. Then, when that air goes through the engine, only 70% of it is actually "burned", so you are proposing that the PCM needs to know that 70% figure, in order to determine the fuel mass rate. But..... if 100# is entering the intake, and only 70# of it is being burned, where is the other 30# going? You could say, well, that goes out the exhaust, due to overlap, or incomplete combustion. But, the fallecy of that approach is that, unless you have added 100% of the fuel mass to match 100% of the air mass, you don't have enough fuel, because if you aren't burning the entire mixture, and some of the mixture goes out the exhaust, that mixture is not just air... it is an air/fuel mix.

The only exception to this would be the air lost due to overlap. At low load/low rpm, it is possible that only air enters the cylinder volume during the initial stages of the intake stroke, the injector is not firing, so only air is escaping out the open (overlap) exhaust valve, not fuel. In that respect, the concept of VE and mass air would work.

But at higher RPM/higher load, once you drive the injector above 50% duty cycle, you are losing both air and fuel, because the injector is firing well in advance of the intake event.

It is entirely possible GM has some concept of VE and how it relates to mass-air systems. But that would not be the traditional concept of VE. All we are trying to do here is understand what this seemingly new concept of VE is, and how the PCM programming handles it.

I really don't know the answer.... I have no need to know, since I don't even use the stock PCM. But I would like to learn the answer.

 

I was trying to explain what the NUMERICAL input in the VE tables themselves meant to the PCM. Not what the VE reading on the MAP means.

 

OK.
Thanks for answering the questions I asked you. Much appreciated.