Basic theory fuel mapping question

[andreNL]

I am trying to understand whats going on in there 
If you map the VE map, your mapping for best burning efficiency
at X rpm with Y amount of fuel at a fixed load.
So force wich the engine has to overcome is fixed so tuning can be done at that point.

Acceleration enrichment is to add fuel to fill in the gaps in the VE map.
But is this wright, because if you accelerate you need lots of more energy to get the mass accelerateted. So tuning the VE is like tuning engine power = drag force
While acceleration is engine power = drag force + acceleration force along the rpm bandwith your acceleration.
At some speed drag is 140n for a 1000kg car
but if you accelerate with 8m/s2 you need atleast 8000n to accelerate wich is alot more fuel to burn. Is this wright or do i make a mistake in the theory?
Cheers andré

[GintsK]

Acceleration enrichment is not for higher acceleration force or making mixture richer. Basically it is just for compensation of [liquid fuel->fuel film-> fulel vaporization->mixture homogenization] lag.

VE table in VEMS case is close to true volumetric efficiency table. So there is just one exact value for each cell. And it describes how much air molecules engine gets relatively to their [volume*manifold absolute pressure].

Where you have some trade-off it is lambda table: here you can tune for best fuel economy (lamda 1.05...1.08) or best torque (lambda 0.85...0.9) or improve burning safety and running richer than that.

Read this ages old document: http://www.not2fast.com/NACA/naca-report-189.pdf

Gints

[andreNL]

Ok but why is the car is accelerating alot faster with alot of enrichment while
just lower the lambda should be enough or have the same effect?
If i turn enrichment off, it accelerates slow but steady and decent.
If i turn it on its like a bomb goes of,

[gunni]

The fuel mapping only relates to airflow and nothing else, not vehicle acceleration for sure.

Your foot is a airflow control device, higher throttle = more air = more fuel required = more power made as more fuel has been burned.

[andreNL]

Ok but if i tune a certain loadpoint with a halve a throttle pedal and let the revs rise,
example 2000rpm to 3000 with 50% tps and do the same with 100% tps
The dot goes Through same table boxes but with diffrent VE values.

If i tune a VE value for power then fuel consumption is crazy under cruising conditions 

[Ignitec]

but you don't need much power for cruising conditions, and can tune low loads for fuel economy. if you tune your lambda table lean (1.08) in your typical cruising conditions (1500 - 3000 rpm, 30 - 60kPa, more or less depending on engine setup and your habits), 0.9 in your typical accelerating conditions, and a little bit richer for safety at top end, you'll get good fuel consumption and power, depending on how hard you drive. small throttle, small comsumption and vice-versa, not both at same time

[gunni]

Ok but if i tune a certain loadpoint with a halve a throttle pedal and let the revs rise,
example 2000rpm to 3000 with 50% tps and do the same with 100% tps
The dot goes Through same table boxes but with diffrent VE values.

If i tune a VE value for power then fuel consumption is crazy under cruising conditions 

Have a better look at your logs, thats not happening.

Sometimes even just 10-15kpa can be a big difference in a engine after a certain pressure.

[andreNL]

Ok will check the logs, so i need more rows and columns. thx

[GintsK]

If i tune a VE value for power then fuel consumption is crazy under cruising conditions 

Please do not make confusion. For VEMS you have just one right value for each VE table cell. VE tuning target is just to find this value. You do not tune VE table for anything else. It is descriptor of engine. That's all.

Mixture tuning is upon to Lambda table. And good thing - you can change it without retuning procedures - you will get what you want. Premise here is 1)tuned injector dead time 2) tuned VE table 3)at least default values in MAT/TPS enrichment table.

[andreNL]

Ok, but finding the real VE value is difficult,
If i use VE analyser and run around to get average values,
the values are diffrent each time, but it should always be the same value.
So i dont understand why the values are diffrent each time?
things to do:
* check rpm and kpa rows
* get a good VE table
* tune lambda for torque

[GintsK]

Results are affected from:
injector lag time calibration (very important for big injectors!). Also voltage calibration!
MAT table
Closer to steady state gives more plausible result. It is quite important.

We have no data about fuel temperature. But it can change result a lot. So take care about good ventilation of dyno room. Or if it is road tuning - cool down exhaust after each power run. Exhaust heats up fuel tank when stand still.

[boostd audi]

50%tps and 100%tps will not result in same MAP reading at same rpm you said 2-3k.. the map reading will be idffernt hence a differnt VE

[GintsK]

50%tps and 100%tps will not result in same MAP reading at same rpm you said 2-3k.. the map reading will be idffernt hence a differnt VE

At low rpms 50% and 100% throttle gives same MAP reading. For this purpose OE units use WOT enrichment or separate WOT tables.
I usually define lambda in low rpm region like this: 100Kpa 0.87 96KPa - 1.0.

[andreNL]

Thx, i am trying and testing the lambda settings and retuning the VE table
I have 460cc injectors and found openingstime is 950uS, i set bat correction at default setting.
I use idle low rpm/kpa 90
Cruise/Decelerate low kpa 105
Above 102kpa 0.86 and looking better