I keep hearing that if you change the spark curve you have to change the fuel and Volumetric Efficiency tables too. I understand what VE is. It is the amount of air that fills a cylinder compared to the amount that will fit.(at 1 bar) But what I really don't understand is why the ECM even cares about VE. What does it do when you change the tables? can someone please explain the purpoe of VE tables nd what happens when you modify them a cetain way. And if you modify the spark or fuel curves why do you need to moify the VE table? I know this is a long question but an help will be greatly appreciated!!

thanks,
Lars

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'92 RS 305 TBI
K&N Open Element
Ultimate TBI mod's (thanks Pablo)
Cam[.442"/.465"] x 218*/224* @ .050", 10:1 Hypereutectic Pistons
Performer Manifold
Shift Kit, Corvette servo,
and 2800 Stall Trans Specialties Converter,
Gutted Cat, IAT Resistor
MSD Blaster Coil, Accel Cap and Rotor

 

The VE tables ultimately affect the pulse width of the injectors at a given RPM and MAP reading (in Kpa). MAP, as you probably know is the absolute pressure...the opposite of vacuum. 29.5" Hg = 100 Kpa = 0" Hg Vaccum.

With the VE tables as you increase the efficiency, the ecm adds more fuel by increasing the PW. If you determine that more fuel is needed at a certain RPM/MAP reading, then you would increase the VE at that point. Conversely, if you felt that you needed less fuel at a certain RPM/MAP, you would decrease the VE at that point.

So that's the basic mechanics. As for tuning, I start with a spark table that gives me minimal knocks. Then I adjust my VE table to the point where I am running 128/128 on my BLM/INT. Then I go back to the spark table and see if I need to remove any spark (due to increased knocks) or if I can add more spark (until I encounter knock).

Then I recheck my BLM/INT values again, and see if I need to further adjust it ... and so forth. Eventually you get to the point of diminishing returns where you cannot add anymore spark without encountering knocks (at the particular grade of fuel you wish to run) and your BLM/INT are steady at 128/128.

I also look at my plugs to see if they have a nice golden tan, listen to the sound of my engine, "feel" the car and give it the ultimate acid test...time it to see if I actually got better performance.

That's just my method...there are other methods which I am sure others will mention to you.

 

BTTT,,,,Anyone else?