VE Scaling

[SS2win]

When I setup my boost tables I scaled to 300% as desribled in the 2/3 bar tutorial. As soon as it hit boost the AFR went to 7:1 and the car bucked from spark blow out. After playing with it a few times I settled on a scalar of 25-50% before I could even *think* about hitting the cells for more than 1 or 2 frames.

Now that the VE is dialed in I'm seeing 11.5:1 AFR as commanded and the VE is only showing 85-90% in the boost tables. The engine seems happy but I was expecting to see closer to 100% VE with the boost and all. My boost controller is set to 8lbs. Does the VE sound ok? Do I have to hit 1 atmosphere of boost to make a significant increase in VE?

[GMPX]

The reason such a high number was chosen was to take into account that somebody may have something setup very wrong like the injector flow table which might cause a dangerously lean condition on the first run, in your case it was crazy rich which was easily fixed, of course you could have run 100% Methanol and you would have been just about on the money :wink:

One last thought, did you multiply the table value by 300% or did you enter in 300% as the VE percentage value?.

Cheers,
Ross

[SS2win]

I zeroed out {A0009}, pasted in 105 kPa colum from {B0101} into the 105 and 285, scaled the 285 column by 300% and did a linear scale.

[QUICKSILVER2002]

Yea, the 300% scale in the tutorial is crazy. It would make sense if it was an actual VE table, but it is not.

The thing that is so confusing about the VE table is that it is not really a VE table. It is more of a mass flow table. People have tagged it as VE and don't really understand how it works.

The % and default units are confusing as heck, if you ask me.

You can calculate the g/cyl and g/sec with the following formulas

g/cyl = ((VE% * 178.33 * 0.708 * Kpa)/(IAT+273)/5120)
g/sec = "g/cyl" / (15/RPM)

VE% - is from the table in the tool
Kpa - is from the table
IAT- is in celsius and you just have to pick one or use logged data
.708 - is the displacement in liters of one cyl on 346 ci motor
RPM - is from the table

To illustrate, Given IAT of 20c and 100%VE value and 6k RPMs.

100Kpa = 336 g/sec
155Kpa = 522 g/sec
175Kpa = 589 g/sec
200Kpa = 673 g/sec

Notice how 1 bar of boost gave you twice the airflow. This is why the % view is confusing if you are thinking in terms of pure VE. It does not require 200% VE for the PCM to calc 2x airflow.

300% VE at 300Kpa would be 3030 g/sec of air. I don't think anyone here will be running over 2000hp.

Hope this helps. I was confused for a few days until I did some research.

I was going to send in a suggestion to allow the Tuning tool to display the table in g/sec or g/cyl. You would have to enter an IAT value, but I think it would be much more intuitive. You could also use your logged MAF values to get you started.

[superls1]

The % and default units are confusing as heck, if you ask me.
...
To illustrate, Given IAT of 20c and 100%VE value and 6k RPMs.

100Kpa = 336 g/sec

I agree that the unit are confusing. How does 100% in the table (2.468 Grams*Kelvin/kPa) relate to 336g/sec? Perhaps Blacky or GMPX could chime in. Just trying to educate myself.

You can calculate the g/cyl and g/sec with the following formulas

g/cyl = ((VE% * 178.33 * 0.708 * Kpa)/(IAT+273)/5120)
g/sec = "g/cyl" / (15/RPM)

VE% - is from the table in the tool
Kpa - is from the table
IAT- is in celsius and you just have to pick one or use logged data
.708 - is the displacement in liters of one cyl on 346 ci motor
RPM - is from the table

Where/how/what is 178.33 and 5120? What do they represent, or how are they calculated? Just curious.

[Dirk Diggler]

I was going to send in a suggestion to allow the Tuning tool to display the table in g/sec or g/cyl. You would have to enter an IAT value, but I think it would be much more intuitive. You could also use your logged MAF values to get you started.

The tuning tool does display in g/cyl edit properties ----> ve calibrations

[Blacky]

The VE table is really a "mass air flow table" as quicksilver rightly pointed out. But I will continue to call it VE because that (unfortunately) is what people know it as and to try and redefine it now would cause more problems than we have time to deal with.

The reason the VE tabe's default units look weird (g*k/kPa) is so that it is trivial for the PCM to convert from the VE table's to the predicted grams of air per cylinder taking into account MAP and charge_temp , as follows:

grams/cylinder = VE*Map/charge_temp

A VE of 2 g*K/kPa at 100kPa and 25degC is:
2*100/(25+273.15) = 200/298.15 = 0.67 grams

Note: charge_temp may be a blend of IAT and ECT based on the charge temperature blending table listed under the VE table in the Tuning Tool.
And charge_temp is measured in degrees Kelvin, which is why we add 273.15 to the charge_temp in degrees C.

The percentage displayed by EFILive is the VE g/cyl value (as calculated above) divided by the maximum g/cyl for the current cylinder volume at STP (standard temperature and pressure, 21 degC and 101.3kPa).

Regards
Paul

[QUICKSILVER2002]

I was going to send in a suggestion to allow the Tuning tool to display the table in g/sec or g/cyl. You would have to enter an IAT value, but I think it would be much more intuitive. You could also use your logged MAF values to get you started.

The tuning tool does display in g/cyl edit properties ----> ve calibrations

You must have a different version than I do. It will display as a % or as default units (Grams*Kelven/kPa), not as g/cyl.

Paul did a nice job of explaining the default units above.

I still think an alternative view of g/cyl or g/sec would be useful. The other #s are just confusing in my opinion.

I find myself pulling it into a spreadsheet for sanity purposes.

[Blacky]

If we displayed a grams/cyl version it would rely on a user supplied pre-set charge_temp. Depending on how far from reality you set the charge_temp would determine how accurate the absolute grams/cylinder would be.

For example, if you set the charge_temp to 15 degC you would see a different grams/cylinder to when you test drove your car the next day and the air temp was 35 degC. That could get confusing.

Paul

[QUICKSILVER2002]

If we displayed a grams/cyl version it would rely on a user supplied pre-set charge_temp. Depending on how far from reality you set the charge_temp would determine how accurate the absolute grams/cylinder would be.

For example, if you set the charge_temp to 15 degC you would see a different grams/cylinder to when you test drove your car the next day and the air temp was 35 degC. That could get confusing.

Paul

I don’t think a g/cyl or g/sec view would be ideal for everyone, but I do think it is much closer to what the table is in reality. Although, the temp would change the value, the displayed/entered value would be relative and relate to the actual physics of the gas laws.

The default units can actually work, but it is sort of like Celsius vs Fahrenheit. It is hard to switch scales when you have trained your brain to conceptualize on one scale. I have no trouble conceptualizing what 512 g/sec of air is, but I can’t even begin to rationalize what 2.888 Grams*Kelvin/kPa is.

If you did a Poll here you would probably find that 90% of the people who did not read this thread would think the VE table displays a regular ve% or g/cyl..

In the end it does not matter all that much, because the values should be based on feedback from the motor, but I personally found it really confusing to get started with the default views. I like to look at the values and determine if they are sane and this is why I have to use a spreadsheet today.