Haltech Platinum Pro 350z - Manual (Page 36)

User Manual – Haltech 350Z
the volume of air, we are really interested in knowing the number of molecules of air that we have. In order to
determine this, we apply the Air Temperature and Manifold Pressure from the manifold to the volume of air that
managed to get inside the cylinder.
8.3 Calculating the amount of Fuel
Given that the amount of air in the cylinder is now calculated, we can now use the Air Fuel Ratio Target to
determine how much fuel is required. The density of fuel is known, so the injector can be pulsed to supply to
required amount of fuel.
To calculate how much fuel goes into the engine when we pulse an injector, we need to know the fuel injector flow
and its dead time.
If the car uses a fuel pressure regulator that keeps a constant pressure relative to the manifold pressure, then this
fuel flow for an injector is typically its size in CC/min.
The dead time of an injector is the time from the start of the electrical pulse to begin injection, until the point in
time where the injector is close to flowing its rated flow capacity. This dead time is added to the theoretical
injection pulse to account for the injector dead time.
8.4 Effects of VE
The main tuning variable for a given engine is the Volumetric Efficiency (VE). The other inputs are obtained
through calibrated sensors or from known quantities.
The VE of an engine is affected by:
1. Intake and exhaust valve geometry, size, lift and timing.
2. Intake and exhaust manifold and port design.
3. Compression Ratio.
4. Engine speed.
5. Pressure ratio across inlet and exhaust.
6. Mixture temperature.
7. Fuel type and vaporization of fuel.
The main parameters that vary and contribute most to changes in VE are points 4 and 5. The VE map is typically
a table consisting of Engine Speed down one axis and Manifold Pressure across the other.
Within this table, the VE can be changed to affect the fuel requirements of the engine. For a given Air/Fuel Ratio,
if an engine’s VE is high, then more fuel will be injected to compensate for the extra air. If an engine’s VE is low,
then less fuel will be injected to achieve this Air/Fuel Ratio.
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