Haltech Platinum Pro 350z - Manual (Page 35)

User Manual – Haltech 350Z
Appendix
8. S
PEED
– D
ENSITY
F
UEL
C
ALCULATION
& VE T
UNING
The Speed-Density algorithm is a method of calculating fuel injection pulse width for a given engine speed and
load. The VE table is a table that describes the volumetric efficiency of an engine.
If you wish just learn how to tune the VE table, then jump ahead to the Tuning a Car by VE and the Speed-
Density Calculation section. The following section covers the concepts involved in how Speed-Density works
which may help in understanding the implications of tuning certain tables and parameters.
8.1 Inputs to the calculations
The Speed-Density calculation uses the following inputs to determine injector pulse width:
o Engine speed in RPM
o Manifold Pressure (MAP, or air Density)
o Air Temperature
o Engine displacement
o Injector flow & dead time
o Air Fuel Ratio Target
o Volumetric Efficiency of the given engine
8.2 Calculating the amount of Air
To determine the amount of air that is consumed by an engine at any instant in time, we use the following
measurements:
1. Manifold pressure from a MAP sensor measuring the pressure of air in the manifold, which is also the
pressure behind the intake valve.
2. The Air Temperature entering the engine from an Air Temp sensor.
3. The RPM from a crank angle sensor.
8.2.1 Calculating Air Volume
By combining the Engine speed, with the known volume of the engine (Engine Displacement), the amount of
swept volume per second can be calculated.
8.2.2 Volumetric Efficiency
An engine is not a perfect air pump however, so even though an engine’s pistons might sweep through a
theoretical volume every revolution, the cylinder is not always filled 100% with an amount of air that is available
from the other side of the intake valve. Similarly, it may not exhaust the full amount through the exhaust valve.
The fraction of air that is effectively moved through the engine, compared to the air that is available in the intake
manifold, is called the Relative* Volumetric Efficiency of the engine.
* - It is called ‘Relative’ because it is compared to the air available in the intake manifold.
8.2.3 Calculating Air Density
When we combine fuel with air, we are combining molecules of fuel with molecules of air. So even if we know
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