Big Cube VE tables

[superls1]

Are the VE #'s really meant to represent actual efficiency or are they just a number that I increase to add fuel and decrease to remove fuel?

Anybody want to post up some tuned VE table values for larger displacement motors? Cam specs would be nice too. Thanks.

[Dirk Diggler]

Make sure your ifr table is represented correctly or you will get crazy looking ve values (too high or too low)

[Blacky]

Are the VE #'s really meant to represent actual efficiency or are they just a number that I increase to add fuel and decrease to remove fuel?

Anybody want to post up some tuned VE table values for larger displacement motors? Cam specs would be nice too. Thanks.

Yes the VE is the actual efficiency of the engine's ability to fill the cylinders with air.
i.e. 100% means the cylinder is full of air
80% means the cylinder is 80% full of air
etc

Based on the cylinder volume, manifold pressure and air temperature, the theoretical maximum mass of air that will fit into a cylinder can be calculated. What the VE table does is tell the PCM how close to 100% of that theoretical mass of air is "predicted" to fill the cylinder at any given MAP/RPM point.

Regards
Paul

[daveb]

I am planning to stroke my engine to 383ci, if I change the displacement in the vehicle info section will it scale the VE table accordingly or will they always remain for a 350ci, meaning I will have larger numbers in the VE?

[Dirk Diggler]

I am planning to stroke my engine to 383ci, if I change the displacement in the vehicle info section will it scale the VE table accordingly or will they always remain for a 350ci, meaning I will have larger numbers in the VE?

You need to scale (B0104} that also since it is used in a few calculations like dynamic_airflow

[joecar]

Paul,

Can I calculate VE as follows...?

1. For various RPMs use the formulas to calculate theoretical volume sucked in by engine in 1 rev; convert volume to mass using density of air.

2. At the same RPMs, take MAF readings; calculate how much time 1 rev takes, and multiply MAF readings by this to get mass.

3. Divide mass from step by mass from step 1; this is VE.

(...assuming the MAF table is correct and the MAF is working correctly...)
(...implies you first have to get your MAF calibration measured...)

Is there a simpler way to do this...?

[Dirk Diggler]

Tune it in SD first and then use the dynamic_cylinder_air values converted to gm/sec and rebuild the maf table...

[Blacky]

I am planning to stroke my engine to 383ci, if I change the displacement in the vehicle info section will it scale the VE table accordingly or will they always remain for a 350ci, meaning I will have larger numbers in the VE?

If you change the displacement, say from 346 to 383, then that's a percentage change of ((383-346)/346)*100=10.7%. So you need to add 10.7% to all cells in the VE tables - after you change the cylinder volume.

Follow these steps:
1. Open your *.tun file.
2. Change {B0104} to 47.875 CI
3. Save the file.
4. Close the file.
5. Reopen the file (notice the VE cells* are now 10.7% lower)
6. Select all cells in the VE table(s)
7. Enter 10.7 in the Adjust box on the toolbar
8. Click the [%] toolbar button.

* if the VE table is displayed as a % you will see lower values. If the VE table is displaed as the "standard" PCM units of Grams*Kelvin/kPa then the values will not be different (because those units do not include any cylinder volume information). Regardless of the display units, you must always add in the % change that you made to the engine displacement.

You will probably need to retune the VE table anyway because the VE characteristics will most likely change with the new crank. But the % change will get you back close to where it should be.

Paul

[Blacky]

Paul,

Can I calculate VE as follows...?

1. For various RPMs use the formulas to calculate theoretical volume sucked in by engine in 1 rev; convert volume to mass using density of air.

2. At the same RPMs, take MAF readings; calculate how much time 1 rev takes, and multiply MAF readings by this to get mass.

3. Divide mass from step by mass from step 1; this is VE.

(...assuming the MAF table is correct and the MAF is working correctly...)
(...implies you first have to get your MAF calibration measured...)

Is there a simpler way to do this...?

Step 1 - I presume you mean theoretical maximum mass of air at a given temp/pressure. If I recall correctly, it's about 0.8 grams of air per cylinder at STP for a 5.7 LS1.

Might as well calculate it out using PV=nRT (or n=PV/RT)
where:
n = m/M (m=mass of air in grams,M=molar mass of air=28.96)
mass of air = PVM/RT
P = pressure 101.3kPa
V = 0.70874 liters per cylinder (5.669 liter engine)
R = 8.314 (gas constant)
T = 294.15Kelvin (21 degrees C = room temperature)
so
m = (101.3*0.70874*28.96)/(8.314*294.15)
m = 2079.19/2445.56
m = 0.85 grams of air per cylinder. But remember that is only accurate at 21DegC and 101.3kPa. It will be different at different temps/pressures.

Step 2 - is already done for you by EFILive - the PID you want to use is grams/cylinder = {SAE.MAF.gps}*15/{SAE.RPM}

Step 3 - I proposed this same method, taking into account the different temps/pressures (back before we did the VE tuning using the BEN factor) and got shot down in flames - but I can't remember why.
It may have been simply that the MAF wouldn't flow high enough values to allow us to use that method to tune 2 and 3 bar VE tables.

There is another way, just use a wideband and EFILive's BEN factor/auto-VE tuning, the combustion process does not lie - unless there is an air leak somehwhere

Regards
Paul

[superls1]

Great info guys.

However, I would still like to see some VE tables for larger cubed motors.

If you change the displacement, say from 346 to 383, then that's a percentage change of ((383-346)/346)*100=10.7%. So you need to add 10.7% to all cells in the VE tables - after you change the cylinder volume.
Paul

I thought the VE changed automatically after changing cylinder volume?
From the VE table info:

EFILive uses the cylinder volume to calculate the VE as a percentage.
Changing the cylinder volume will change the VE percentages displayed in this table.

I am sure that I just need to play more, but I am a newbie and learning so please forgive. Are you saying that if cell says 50 when CI=346, when changing cylinder volume to equate to 383CI it will then read ~45. Therefore, I must increase it by 10.7% to get it back to 50? Would this then be my base for starting my VE tune?