Can someone explain the overall shape of the VE table? Why does it peak at around 5300 rpm then fall back? I have only tuned this table up to about 4000 rpm, the rest is stock. I understand that as the MAP increases, the motor will become more efficient thus the higher %.


I just want to get some discussion going on the reasoning behind some of the trends in the plot.

Jeremy

 

Top end fade is the flow restriction posed by all of the stacked
up resistances - intake and head runners, the inerta of the air
column vs the cam-open chop time, the spent gas residual
pressure in the cylinder.

The over-100% peak in the middle can be resonant intake runner
effects building out the cylinder fill (or, just a cheat to make it
fit mixture-wise).

My opinion is that the motor is a fairly regular, continuous pump
at the heart of it all and the response surface should be smooth
and continuous. I don't like the look of that "pocket" at the lower
MAP, 2800RPM or so. Unless this has EGR or something to depress
the air, that looks like a lean divot.

Also the area above peak, where it drops a little and then plateaus
on out to 7200? Not too realistic, even though you probably don't
go there. More like "drop and keep on dropping", this is where the
big cam will carry you on out but a little cam will starve the motor
for air (open time).

I don't have a good idea of why MAP would increase VE (MAP already
being in the SD equation, RPM*MAP*VE(). Maybe it's about more MAP
overcoming the residual pressure, or MAP making the air column scoot
better at the beginning of intake cycle. Something has to fit up the
air column start/stop/resonant effects.

 

good reply. I am still waiting on my EIO before I get to into the VE tuning, but this was done only with fuel trims. The "puddle" as I like to call it, is the result of about 10 tunning sessions. I smooth it out, and it comes right back the next time out. I have a decent sized cam (230/238 .591/.605 114), should I extend the peak a little higher in the rpms? Like I said, I have only tuned to about 4000 rpm. I was just messing around waiting on the EIO.

Thanks,
Jeremy

 

From what I understand, the shape and rpm range of the VE table mirrors the TORQUE curve from a chassis/engine dyno run. IE, if you make peak torque at 4900, the VE table should rise to 4900, then fall after that. I do not think that it mirrors the hp curve. If it did, you would see VE tables rising to 6000-6500, then falling off.

 

YES! I think so too. The VE determines the amount of fuel put in. The amount of fuel put in determines the amount of power. You could in theory take the grams of air going into the engine, multiply it by the AFR to get the amount of fuel, look up in a thermodynamics table how much energy that fuel is worth, convert it, slap a 20% efficiency on it and that should be somewhat close to your horsepower!

Also, couldn't you take a dyno run and back-figure it to a VE table?? You should be able to!

 

How come that graph shows percent? What number is it based off? It is not in grams or any tangible, measureable unit. The area where it would idle at looks kind of low, right?

 

I'll have to go get a pic, but my wideband tuned car mirrors EXACTLY my torque curve. Peaks right at 4800, drops off after that.

 

Air mass = VE = power = torque...

 

how do i get mine to "roll"? ive tuned and tuned and still cant get my ve to do it.

 

Here's my VE graph:



And the table that goes along with it:



My car is bolt-on only, tuned open loop speed density. If you need the mod list, just ask. Pretty much just full intake/exhaust.

 

heres what mine looks like.

 

I think ninobrn99's VE table can not accurate. At lower engine speeds, VE will be reduced due to heating of the incoming air.

 

hey gary, what timing tables are you running? stock or zo6? ive turned off dfco so it shouldnt richen up. i think. i just threw the ls6 timing tables and put it back in SD, so im gonna see how that works out.

 

How are you suppsed to build a VE table if you dont have a MAF (i.e. no reference for airflow)????

In SD mode you only have MAP and RPM... no airflow...

 

ltrims or with a WB

 

Aren't you supposed to tune the VE table for all the same air temperature and then you use the Fuel-Air Multiplier to correct for incoming air temp situations?

 

You just have to rely on a wideband O2 sensor to tell you what's coming out the other end. IMO, it is the ONLY way to tune a car. Narrowbands are only accurate at stoich, and then really only if you have stock exhaust manifolds, as they just don't work as well with headers.

I don't even use narrow band O2 sensors anymore...the bungs are plugged from now on on my car.

 

If you think about it, you really can't tune to just one air temperature, as the IATs are gonna fluctuate during normal driving conditions. Now, with SD tunes, you do need to make sure your operating ECT is fairly constant, as your commanded AFR in the OLFA table doesn't exactly correlate at other ECTs.

Basically, you just gotta tune it like you drive it.

 

I believe IAT is in there as a correction factor for density->mass
but the IAT is only going to be right, at steady state (and maybe
not -that- right, at low flows if heat is transferred after the IAT
location).

Regardless, it's pretty unlikely that VE would kick up at the high
RPM end of the table.

Here's a table I fitted for a TRex cam (over the email) by using
open loop NBO2 voltages....

 

Speed density doesn't necessarily mean open loop, although it sounds like you're running sd and open loop.

If you see your closed loop tune acting up when the temperature changes it's not cause the sd tune can't compensate for temperature. I would look for a fix in the charge temp bias vs airflow table.