VE Tuning Basics

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VE Tuning Basics

Postby HaltechScott » Fri Aug 13, 2010 12:54 pm

VE (Volumetric efficiency) tuning is great - The car runs better and will certainly get better economy over injection time.
How it works-
The ECU needs the following information:
Injector size
Injector dead time
Engine size
MAP sensor
Air temp sensor.

What it does:
The ECU looks at the injector size to know how much fuel can flow through the injector (in a perfect world)
It looks at the injector dead time. The injector dead time is the amount of time it takes to physically open the injector. If the ECU knows this dead time it knows the "actual injection time"
Engine size (Eg. 3000cc, 3L )
MAP sensor input - To measure manifold pressure
Air temp - the temp of the air will change its density, "allowing" it to carry more or less oxygen.

The final piece of the puzzle THAT NEEDS TO BE TUNED is the VE map (main fuel map). I will talk about a turbo car in this example.
Because we know about 4 stroke engines we know that they idle around 50% efficiency and flat out are around 90-105% efficiency. This makes it easy to make a base map. Around idle 50% (up and down the WHOLE column) flat out 100%. then linearise left to right on the screen (picture below)
Start the engine and see how it runs and revs.

Note - Our VE calculation accounts for boost pressure. 15PSI of boost will not add 100% efficiency - Simply dont think about this.
Note - This Calculation has been proven many times - Its not wrong!

The VE number can be from 0 - 200, even though not technically correct to have a VE of more than 105ish it can happen due to calibration errors - See below for help on how to get the numbers in the right area without all the hardcore tools to check (covered down the page).

Because we know the size of the injectors and how many injectors, the actual injection time, air temp, MAP and size of the engine we know how much fuel the engine is getting depending on the entered VE number (how much each cylinder fills up every engine cycle (the VE!!!))

Common Potential problems:
Injector dead time not accurate - This will give funny VE numbers.
Injector size incorrect - This will give funny VE numbers. Remember injector size is heavily dependant on fuel pressure. We typically assume a 1:1 fuel pressure reg. you can choose constant fuel pressure or 1:1 reg (IF you have a higher ratio reg the VE numbers will be funny looking).
Engine size incorrect

To avoid these issues try the following.
Set the engine size (you should know this)
Set the ADVERTISED injector size (this will certainly be out slightly)
Use the DEFAULT injector dead time map (unless you have all the correct tools and can accurately measure it - less than 2% of the population!)
Now in the fuel map you should have a number of 50% VE at idle.
Adjust the WHOLE injector dead time map up/down until the engine idles at the desired AFR. This will give a "cheat" calibration for all the small errors in injector/engine/dead time sizes.

Lets say you want to run E85 in your car.
Set the Target AFR Map to the AFR your wideband reads ( when set to 10-20afr gasoline) when running the e85.
For example. You would target 9:1 AFR at cruise and idle. You would target 7:1ish flat out.

Notice how you have a very close base map already - Feel free to let me know how you go with this bit of help.
Ve Demo.jpg
Ve Demo
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