Volumetric Efficiency Load Scale Question

[Noodleman]

When i make changes to the load fuel/ign scales, do you have to do this to the volumetric efficiency load scale as well? What is volumetric efficiency used for?

[Matt]

The VE scale is used to trim against the fuel map

You will notice the scales of the VE on RPM/TP axis are smaller than on the fuel map. You will also notice the fuel map has a majority of its AFRs about the target of 14.7:1 with ECUs that have a VE map

The fuel map seems to have the traditional O2 flag always on also. I'm not sure yet why this is done, but thinking perhaps O2 feedback is used over the entire fuel maps where VE is used

Try to keep the VE scales as a subset of the fuel scales like how they are from stock

Modifying either VE tables or fuel tables will adjust the injection pulsewidth

However the idea is that you set your fuel table for the desired AFRs that you want, and then alter the VE tables to trim the output AFRs until they match your fuel map

For the high load/rpm areas not on your VE map adjust these areas directly on your fuel map

[Legionnaire]

Matt, while we are on topic, I'd like to ask.
If fuel maps have O2 feedback always on, how can I produce airfuel ratios leaner than stoichiometric? And what do values in VE map cells really represent? I guess 128 raw is 100% VE, where real world AFR is the nearest to fuel map AFR, larger value means VE above 100% hence more fuel required, smaller means less consumed air, so less fuel. Is this true? So, to generate leaner than stoic mixtures I set target AFRs to 14.7 then reduce VE.
Does VE map work this way or am i mistaken here?

[Matt]

You will need to adjust the VE map cells to make it leaner less than stoichiometric

128 = 100% as you mentioned. greater than increases the injection pulsewidth from memory last time I checked this. If you monitor your injection pulsewidth whilst adjusting this table you will soon notice

[Noodleman]

interesting, ill probably leave it alone for now till i get a shop to tune my car.

[Legionnaire]

interesting, ill probably leave it alone for now till i get a shop to tune my car.

I think if you are going to be tuned anyway you should possibly set all values in VE map to 128 to avoid tricky effects on AFRs and save yourself and your tuner some time

[Noodleman]

how would changing all the values to 128 have an effect on the afrs? Currently im experiencing lean mixtures on boost could that be because the VE tables are not set correctly?

[Legionnaire]

Lean under full load can be because of 100000 reasons
The idea to set all values in VE table to 128 before tuning process is that you will not wonder why in one cell you see mixtures richer then in target afr table and in another cell it is leaner. 128 in all cells is to even out relation between afrs as set in target afr map and real afrs across entire map.

[Noodleman]

Ohh i get it, so is it ideal to just set the ve table values to 128 and leave it there permanetly or temporarily until the tuning process is done? Im taking it to a shop to fine tune so they would probably adjust the VE values accordingly.

[Legionnaire]

IDK how this works on KA24, but on my RB25 I'm unable to set mixtures leaner then stoich using target AFR map only. It can be done though if I set target afr valuse to 14.7 - leanest possible on this map - and decrease VE value from 128 in corresponding cell on VE map.
So the idea, as I see it, is to start with all VE table values set to 128, all target afr map values set.. well, to target afrs . Then you adjust target afr table for high load/high revs and adjust VE map on light load/cruise conditions using its higher resolution in that area, where you may want leaner then stoich mixtures for economy.
Generally, I think adjusting VE cell for any particular load/rev condition has less impact on AFR than adjusting target AFR cell for that condition.

[UNISA JECS]

Hey Matt you notice how the VE RPM scale only goes up to a certain point? I was looking at some dyno's and I dont know if its a coincidence but it looks like the VE RPM scale goes up to the peak torque RPM? Is there any relationship here?

[Matt]

I think it goes upto the point where the 14.7:1 on the fuel map finishes to only is used for about 3/4 of the fuel map

[UNISA JECS]

Some good information

[UNISA JECS]

I actually think the VE load scale is fouled up, heres why I say this, because when throttling the engine the VE load scales maxes out at 128 which equals roughly 2.0v from the TPS sensor.

Below is a short video I uploaded from my cell phone showing how the VE load scale works once re-scaled up to 255.

If you leave the VE load scale at 128 you max out always at half throttle and at idle its already accessing like the 5th row also.

VE load scaled is scaled to 255 in the video below (video quality was much better on my phone)
http://youtu.be/63Jje7lDvvA

[UNISA JECS]

Anyone with an OBDII or ECU that has the VE load scale test it out for yourself you'll see how quickly the load scale flys off the map I just don't think that's correct, you can also see this with just the ignition on the car doesn't have to be started.