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VE value's not as expected when running boost

Practical Standalone Tuning

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i have a question about the VE value's

and please correct me if i'm wrong

my interpretation is that if you fill in the correct value's for injector size and engine parameters voor de VE value's you would expect

also the VE value's more in the range

for example with a NA engine full power run on let's say around 100KPA you would expect a number somewhere in the range of 85 to 100% is it

i see in some video's where the VE value in turbocars. have a VE of 100% when it is running 160KPA so 0.6 bar of boost i would expect is the engine has a VE of 90% with no boost you would have a number closer to 130% - 150 % VE

is there alos a factor of fuel pressure involved in this like when your running MAP pressure on the fuel pressure regulator

and the fuel pressure is also 0,6 bar higher it will inject a little more fuel??

Regards Johan

When using a MAP referenced fuel pressure regulator, when MAP is 1.6 bar, and the fuel pressure sensor (which is normally relative to ambient pressure) reads 0.6 bar higher, the differential fuel pressure (fuel rail pressure - manifold pressure) is still the same. So there should be the same amount of fuel injected for a given injector pulse time.

BTW - modern 4-valve engines with good intakes and exhaust systems can achieve greater than 100% VE at peak torque when normally aspirated.

oke yes

when looking then to a more modern VE the VE should be much higher then the example i'm giving is it ??

It may be higher -- depends on the engine, cam lift/timing, compression ratio, etc.

You really don't need to worry about the absolute number, when tuning, just give the engine what it needs to hit your fuel mixture targets.

hello David

i understand that you just give it what it needs but to set a good base map to start with there is alot of difference and my question is why is this

i guess it is because of higher VE then in theory is to low value for calculated injector size

i have attached to files ,

1 is a map from the course with from the NA engine with a VE like i think it should be when the REq fuel calculation is correct

100KPA or no vacuum gives around 100 VE on MBT but on the VE turbo map the VE value is also around 100% when running 200KPA so that is 1 bar positive boost pressure.. i would earlier expect around 180% or something

when i make the base map with reh right fuel req. for the engine and make the base map for the NA and later on go make the base map for running boost what value's do i use then when i fill in 100% VE at 1.6 bar this is then to low is it ?

Regards, johan

Attached Files

I would think of VE like just a correction factor where 100 percent is matching theoretical 100 percent displacement filling under normal conditions ( 0 degrees C, 0 humidity, 1 bar absolute pressure). So you need to compare how much air actually gets into the cylinder under specific conditions and divide it by theoretical 100 pecent volume filled with air under normal conditions. When doing so you will always be somewhere around 100 pecent maximum unless you are running NA engine that can exceed 100 percent value quite well. But there is one thing that is not very convinient about using VE is that you deal with voulme whilst engine operates with units if mass. When you use units of mass instead of units of volume you get engine load value which is very easy to understand - actual mass of air trapped in the cylinder divided by theoretical mass of air that can occupy this displacement ( under normal conditions) equals load. When working with units of volume you have to do it backwards and calculate ( using ideal gas low) volume via units of mass under normal conditions.


the amount of mass filling the cilinder at the same temp will have the same range as VE if the temp is going up or down this will have a correction map i think

if you have an engine that can run a VE of 100% in NA operation on 100KPA. if you run this same engine with a turbo and run 150KPA so ,5 bar boost

you will need to see at this point a VE of 150% exlcuded what the temp is doing

when running 150kpa on that point the cilinder filling is 1,5 times normal so also 1,5 times the fuel should be calculated with the afr number at that point

My point is when seeing al these VE table with different value's that are not showing the real VE number. i think this is because of the not fully correct fuel req calculations.

for example i have a car that is running on a VEMS ecu that also is useing VE fuelmap this car is adjusted on the dyno by an other tuner . this is a NA car. the highest number in my map is 215 % VE this can never be correct if the fuel REQ calculation is done correct

why i opened this topic is because in the roadtuning course there is show how to set a base map to start with this is the VE table i added to this topic above

this is around the 100 % value max. ad my opinion the correct way . but in the turbo car tuning on the dyno the numers are also 100%

i'm looking for info how to set up the base map above 100KPA when running for the first time in boost . to get close tot he AFR correction map.

You cannot exceed VE much more than 100+ percent. VE is correction factor, not measuring factor. In your case you need to measure how much air got into the cylinder with 150 kpa manifold pressure at specific temperature,then recalculate it to normal condition and figure out how much room in the cylinder it would take (using ideal gas low and other math for humidity), then divide it by 100 ( 100 percent filling under normal conditions in the same cylinder with same 150 kpa manifold pressure). That would give you the correct ve fugure. You do not need to add boost to the VE as you calculating some figure by doing that. Instead you need to calculate how effective cylinder filling is comparing to ideal 100 percent. In most cases the actual effectiveness is less than 100 percent.

I don't think this is how it should be more air means more filling % so more fuel is needed

More air means more load ( more mass). VE represents the effectiveness of engine breathing wich is actual filling vs theoretical filling by percentage... That is all there is to it.

explain this then

Attached Files

explain this then

Attached Files

Well, to me if you need 200 percent VE to get your actual lambda match comanded lambda weither the actual size of your fuel injectors is two times smaller than stated in tune file, or actual fuel pressure is twice less or it is a combination of both.

Some ECUs using the VE just like you were trying to figure it out (90+50 etc) but to me it is total misconceptions of what VE means.

The "V" in VE means volumetric. The swept volume of the cylinder doesnt change with pressure or temperature and neither does VE. Pressure and temperature is only needed later in the calculation to derive charge density and mass (mass is the final variable you are trying to calculate to be able to add the correct mass of fuel).

For the sake of argument, if you ignore the effects of compressor and turbine efficiency etc, if your engine has a VE of 100% at 1bar boost, it will still have the same VE of 100% at 2bar boost. Just when you convert that volume into mass the 2 bar example will be twice as heavy because the pressure and therefore density is. The law is PV = nRT.

Your VEM's VE table examples are obviously wrong as you have a VE of near 100% at idle, most likely an injector flow rate or fuel pressure difference.

@georg1970 yes that is the same as i thought the took smaller injector volume for the calculation

@georg1970 @Adam@link_ecu. i had a look again at the VE files let say every step of 10KPA up is 3% more VE as average up to 100KPA if i want a base map upwards to 200kpa i can just take every step up also 3% more VE so to 110kpa 3% more 120KPA 3 % more and so on to get a base map is this the right way to do it and then run with save timing and the use the AFR correction to fine tune the VE for these point's?

Sure you can use educated estimation to predict figures in VE table. Safe ignition timing always needs to be used for initial runs until ve table is correct.

As the guys have already said think of the VE table as a multiplier to a base injector pulse width which is in turn relative to the size of injector and fuel pressure (mass fuel flow). Depending on the prerequisites this VE table will bare no resemblance to the actual volumetric efficiency.

For an NA engine Volumetric Efficiency is perfectly valid given the somewhat constant pressure, with forced induction we need to consider that the increase in pressure will effect the Mass flow rate more than the volumetric flow rate given the change in density - compressor and charge cooling efficiency not withstanding.

As a basic 1st pass to calculate actual volumetric efficiency start with mass fuel flow multiplied by AFR to give mass airflow and divide by density.

have a scan at http://www.epi-eng.com/piston_engine_technology/engine_technology_contents.htm for a well informed background and John Heywoods book on engine fundamentals for further study; Stone and Heisler also wrote some good books on engine principles if you're still interested.


I Will have a look at the link and the Books

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