Question on Volumetric Efficiency

[Teeeman]

Alvin,

I saw in the last version of my tune you had dramatically altered the volumetric efficiency table.

I think I understand the base definition (how much air the engine is actually moving ratioed to the max displacement... i.e. if it moves in 300cid on a 350cid engine, that is 85.7% volumetric efficiency... ?).

But with regards to tuning and drivability, how does it work? When you change a value in the table, what effect does it have on the engine and its operation?

I know by reducing the lower RPM vol eff settings on my car, it seemed to lean out quite a bit... is this the right direction of thought?

Is it an iterative loop (lower vol eff would be telling the computer there is less air... so it would squirt less fuel... thus the actual net effect is you lean out the mix... is this right?)


I thought the vol eff tables were primarily how you compensated for head/cam differences...


Thanks!


Terry

[Fastbird]

Your understanding of the VE tables is a lot like my understanding of them also, if that helps. For what I know:

The VE tables are the main fueling tables on our tunes and as such: Lower number = less fuel and Higher numbers = more fuel.

[pcmforless]

Yep you got it right.

VE is where the action happens. All cars can stand to use a VE tuned out. Cars like yours are critical to VE tuning.


For whatever reason on your last tune I thought I would give you my VE tables as the cars are pretty simular. it didn't work out because my car is at 9:1 compression and is severly less effecient at lower RPMs.


As soon as we get good o2 sensor feedback I'll resume tuning your VE tables in with the calculators I built. Somethings up right now, as you are with in 7% correction on VE yet you have a few driveablity problems that can be associated with VE. My thoguhts are we probally fouled them out or something at one time.


For whatever reason my stock O2's are severely screwed. I tried tuning the car on them just a week or two ago and the tune went to all hell!! Went back and tuned it with my on board wideband and the car straigtend right out.

Soo.. I guess what i'm saying is tuning is only as good as the feedback you use.

[brandboZ28]

A thread like this tells me two things...

1. I still have a lot of learn about these cars

and

2. We got some smart m'fers up in here. :D


Sorry to hijack but I just thought Id share that tidbit of info. :dunce: Theres good info in this thread though. I learned something new. :thumb:

[Teeeman]

Alvin is the king of brains around here, IMHO, when it comes to the PCMs.

Nobody else has plowed the SD fields like he has... some of his products are unique to SD cars... but I know of NO ONE offering a hack to achieve 2-step performance from a stock PCM... that is just, in a word, WOW!


Fastbird and Knightfire are extremely knowledgeable as well.

I cheat, I shot Alvin an e-mail BEFORE I posted this question :D



-T

[Teeeman]

I am very interested in possibly going to real-time wideband Alvin.


What is required?


If I have to replace my O2s anyway, it just makes sense...



Terry

[pcmforless]

Wide band is very simple.. I have a .ads file that works with tunerpro RT that displays AFR as long as your widebands output is a particular formula (Voltage vs AFR)

the hardest thing I got working was the 2 bar.. that crap was tough

[Teeeman]

To replace the factory O2s with wideband, do I need 2 wideband sensors?

I have the wideband info you sent me at home (some time ago)... have you changed your sensor preference in the last year?




Terry

[pcmforless]

No you only need one Wideband o2.

[harvickgm]

wouldnt it just be easier to buy the commander system and keep an eye on it at all times and you can even datalog it to a laptop. im going to leave the stock O2's and add the wideband in the header and run from there....
hey alvin, explain the 2 bar map sensor. and i have heard of a 3 bar, do you use these when applying boost, kinda like the difference in readings between a narrow and wideband O2???? i have been wondering this one.....
and another question, this has been on my mind for awhile just never asked... in the VE tables is this where the major changes are made when you do a cam change?? you just play with it until you get the right fueling for the cam and maximum power out of it??? and is it true that these cars from the factory were tuned alittle rich and the best thing to do with the tune is to lean them out first??
sorry about all the questions but these have been on my mind for awhile. thanks man

[Teeeman]

I had some free-time on my hands and someone hit my favorite topic...

forced induction mods :)

http://www.speeddensity.org/showthread.php?t=385


Think it will cover the 2bar thingy pretty well.


Lot to read... just be patient, it is there.


Terry

[harvickgm]

so basically the 2bar has a wider range of sensing ability like the wideband O2.... is that right
its needed because the stock wont pickup the amount of boost. so you need a better wider band sensor for the computer to work correctly...right???

[Teeeman]

A stock O2 at least has a chance to read the range of even heavily modified engines if the tune is close... key words, IF the TUNE is CLOSE...

with a wideband, you can see just WTF the engine did, no matter what, and fix it.


With a 1bar MAP, if you run boost, you are BLIND AS A BAT when you enter the boosted regime of engine operation.


-T

[harvickgm]

hey alvin, what all is needed to convert my whole car/computer to wideband. and what do i need from you to do it. do i need the Real Time tuner???
im interested in to what i need to do this

[pcmforless]

You dont' convert it all over.. You simply tie it into a sensor that way you can read what the car did at home.

Its just a datalogging tool

[harvickgm]

so you just add it to the bin file and remove one O2 and replace it with a wide band and wire it in and you can read it when you data log??

[pcmforless]

No, look what I just wrote..

You get a hand held wideband unit. Most come with a 0-5v out. You take that output and tie it into a sensor that you dont' care about anyway.. like fuel pump voltage, ac pressure high, etc.. then you come home and observe the data to see what the car did.. it has no affect on the way the car ran. it jsut records wideband along with other sensor data

[harvickgm]

oh, ok, i thought you meant that you found a way to convert the PCM into a wideband system. ok sorry, read that wrong. so i guess im still stuck with the commander system

[Teeeman]

My understanding thus far (Alvin jump in if I'm wrong) is you add the wideband sensor IN ADDITION TO the stock O2s.


The wideband comes with a bung that must be welded to the exhaust... and a plug for sealing it off when you are not using the wideband.


Just as Alvin said, for data-logging ... you add the wideband and use the DATA to tune the car.

The car will still be running off the stock O2s.

I think some a-market systems (FAST?) use the wideband full-time for operating the car, not just for tuning.



Terry

[harvickgm]

my wideband is going to be permanent, i dont know if you have heard of the commander. is a widband with a in car gauge that gives you instant AFR readings at eye level at all times. it runs about 450 just saving up and waiting to do it

[Fastbird]

my wideband is going to be permanent, i dont know if you have heard of the commander. is a widband with a in car gauge that gives you instant AFR readings at eye level at all times. it runs about 450 just saving up and waiting to do it

I'm semi-familiar with the kit. What it DOES NOT DO is take the place of your stock O2's. You still need those to help the car keep everything in check. The only computers that work with wide bands (that I know of) are the aftermarket DFI systems.

[harvickgm]

yea, i knew that already. i have already setup the header for the wideband O2, just waiting to install it thats all

[rkinney]

I am interested in this also. I have tunerpro rt, but do not have the .ads file to datalog. I also have the lm-1, so I am assuming that I can output the afr to tunerpro rt with the correct .ads file and the (voltage vs. afr) formula. How do I go about getting this .ads file. I would really be grateful for some more info on this file and formula. I cannot get my rpm converter to log rpm correctly so I cannot plot rpm with afr and map on the same graph to analyze.