Electromotive TECgt User Manual Download Page 58

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Linear Thermodynamics

There is no RPM-dependency for the raw fuel curve derivation. The governing principle behind

this is that the pulse width requirements for an engine with a smooth (flat) torque curve will not have a very
large RPM dependence. Rather, the pulse width requirement will be mainly load dependent with only a
small RPM dependence due to volumetric efficiency variations (i.e. torque peaks at specific RPM points).

To summarize this principle, an engine at 100% load will require 100% of the pulse width value

defined by TOG. An engine at 50% load would require 50% of the TOG, and an engine at 0% load would
require 0% of the TOG (the MAP sensor determines the load percentage). Electromotive refers to this as
“Linear Thermodynamics.” Keep in mind however, that the Linear Thermodynamic principle is a
simplification that is useful for getting an engine up and running quickly. High-RPM engines that have a
weak torque curve at low RPM’s will stray from the thermodynamically linear assumption. Turbocharged
engines that do not start to create boost until high RPM’s will also stray from the thermodynamically linear
assumption. However, these engines can still be tuned quite easily by choosing appropriate values for
TOG and IOT, then manipulating the Volumetric Efficiency table and TPS/MAP Blend Parameters.
Engines in which the MAP sensor is a good indicator of engine load will typically adhere quite strongly to
Linear Thermodynamic principles. Indeed, most production engines (even modern DOHC engines) can be
made to run acceptably well with no Volumetric Efficiency Table offsets to the raw fuel curve, even when
outfitted with individual throttle-per-cylinder setups (using the TPS/MAP Blend Parameter)! However, it
is recommended that the Volumetric Efficiency Table be manipulated once the engine is running
acceptably well to attain optimum drivability and power.

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Volumetric Efficiency Corrections

To provide both RPM and Load corrections for engines that stray from thermodynamic linearity, the

TECgt

software has a Volumetric Efficiency (VE) table. This table allows corrections to the raw fuel

curve at all rpm and load points. This is quite useful for high revving and turbocharged engines, since they
often have very non-linear torque curves. Adding the VE correction to the pulse width calculation:

Pulse Width = [(MAP Voltage

TOG

(VE “Absolute” %

100)]

IOT

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TPS/MAP Blend

Engines with high-overlap camshafts or throttle-per-cylinder setups (Hilborn-style) often experience

erratic MAP sensor operation at low RPM’s; particularly around idle. The main problem is that these
engines will either produce a non-consistent or weak MAP signal at low RPM’s. To compensate for this,
the TPS/MAP Blend feature should be used. This feature allows the low, constant voltage of the throttle
position sensor to be blended with the erratic, weak MAP signal at low RPM’s. In effect, it “tricks” the

TECgt

into thinking that the engine is operating at a lower manifold pressure (higher vacuum) with a

consistent MAP sensor voltage.

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Other Corrections

The fuel pulse width is also affected by the enrichments imposed by the TPS acceleration (TPS),

coolant temperature (CLT), air temperature (MAT), oxygen sensor correction (EGO), starting enrichments
(SE) and battery voltage (BTO). With the exception of BTO, these enrichments all

add a

percentage

to the

“VE Absolute %.” Conversely, the BTO adds a

fixed amount

(not a percentage)

of injector pulse width

response to battery voltage.

Pulse Width After All Enrichments =

{

(

MAP Voltage