Intro to the Speed Density algorithm and the Translator Pro approach to tuning and control.
The Translator Pro is a high-tech engine tuning device intended to fill the "technology gap" between the popular but simple piggyback tuning devices and the full-blown, expensive standalone engine management systems. The Translator Pro uses sophisticated computations to determine engine airflow, thus relieving the user of the daunting task of completely mapping the engine's operation. Once the initial setup is complete, there is usually little tuning required to attain smooth operation and driveability.
The Engine Control Module (ECM) or Engine Control Unit (ECU) in a vehicle is a small computer unit responsible for calculating how much fuel is injected into the engine. The fuel is injected to match the air flowing into the engine. The Translator Pro, like all "piggyback" controllers allows the user to adjust the airflow measurement, thus changing how much fuel the ECM/ECU injects into the engine. This is how the user "tunes" the engine. The Translator Pro is unique in that it allows the user to remove air measurement devices (MAS, MAF, VAF, etc) from the engine and use a speed density calculated signal to replace it. In high performance engine applications this has many advantages and added flexibility.
The Translator Pro, in its standard Speed-Density configuration, calculates engine airflow using the laws of physics, which makes the tuning adjustments much simpler than many competing units that require a large amount of data be entered just to get the engine to run.
Speed Density calculates engine airflow as follows. Consider a theoretical " 4 Liter" engine for the following explanation. The engine can be thought of as a pump that, at 100% efficiency, will move 4 liters of material from its inlet to its outlet every 2 revolutions or the crankshaft. At idle the efficiency is mainly controlled by the throttle blade and somewhat by the camshaft/valve timing. At heavier throttle the efficiency is mainly affected by the camshaft and valve timing and mechanical efficiencies of its construction. The material that is being moved by this pump is air of varying pressure and temperature. Since we can measure the pressure and temperature of the air entering this engine, we can calculate the air being pumped through if we know the efficiency. This efficiency is known as the "Volumetric Efficiency" and is the main tuning element of the Translator Pro's Speed Density algorithm. The Translator Pro then uses the calculated airflow number to generate an airflow signal to send to the ECM/ECU. The ECM/ECM is unaware that the air measurement is coming from the Translator Pro instead of the original measurement device, and will deliver fuel based on the new airflow signal.
Volumetric Efficiency (VE) is the main "tuning" element in the Speed Density system. VE is generally around 55 to 66 percent at idle. At mid and heavy throttle the VE is highest (85 to 95 %) at peak torque RPM. VE tends to fall at high boost and RPM on turbocharged vehicles due to turbo backpressure. On the Translator Pro, the VE table is preprogrammed, but can be easily changed using the PC interface program. The default VE table is close enough for most applications, and the keypad tuning methods can be used to fine-tune the system.
With 3 load levels 14 rpm bands and = or - 60% tuning in 1/2% increments. The MAF Translator Pro stands alone in aftermarket tuning devices.