A Comparison of Fuel Mangement Schemes

A Comparison of Fuel management Schemes.
Fuel Injection Summary	Pressure Sensing/Speed Density	Mass Flow	Flapper Door	Throttle Position Sensing/Alpha-n
Primary Input	Manifold Pressure	Mass of Air	Volume of Air or CFM	Throttle Position
Other inputs required for calculation of mass flow to find injector flow rates	Temperature Volume	None	Temperature Barometric Pressure	Temperature Barometric Pressure
Best Use	High output engines Turbocharged / Supercharged engines Engines with alternate manifold designs	Low hp Normally aspirated applications Engines with Plenum style manifolds	Low hp Normally aspirated applications Engines with Plenum style manifolds Engines with very docile camshafts	Racing applications where very high lift/duration camshafts are used Single stack type manifolds where a proper pressure reading is difficult to obtain
Errors encountered in Calculation	Transients during fast changes of throttle due to lag of pressure change behind flow, easily corrected with throttle position sensor acceleration tables. Volume changes due to volumetric efficiency of engine, easily corrected with mapping.	Very difficult to calculate pressure when calibrating turbocharged engines	Pressure is rarely measured, a barometric pressure switch is used and is merely a gross calculation. Tendency to over swing on throttle changes, causing excessive acceleration enrichment	Acceleration enrichment needs compensation Small changes in engine efficiency greatly affect calibration Any change in engine, either mechanical or calibration, alter all other parameters making it very difficult to tune accurately
Key Benefits	Lowest restriction due to lack of air flow measuring device. Manifold design is open without limits of porting to single air flow measuring device. Calibration for turbo engines enables optimized tuning at all boost pressures with ability to safely manage over boost properly.	Long term mass flow accuracy, good for emissions equipped vehicles with low horsepower ranges. Lower restriction than Flapper Door Type air flow sensors	Better accuracy than carburetors	No limitations on camshaft design No limitations on manifold design
Disadvantages	Changes in Engine efficiency over time are not compensated for in calibration. Oxygen sensors can remedy this with closed loop for street engines.	Poor low speed resolution on high output engines. Resolution is sacrificed due to high flow capability of mass flow device and poor air flow at low engine speeds where drivability is critical. Flow measurement in both directions creates problems on turbocharged engines due to large volume of air returning on throttle closure.	High restriction due to spring loaded door. Very limited flow range Unreliable for long term durability due to moving parts and resistor element wear	Poor low rpm/light throttle resolution for calibrating Recalibration in short intervals necessary Does not compensate for any mechanical changes in engine
Primary mapping method used for calibration	Single large table of pressure vs. rpm enabling a wide variety of conditions to be considered	Idle Map Part Throttle Map Makes mapping difficult with transition from part to full throttle especially dealing with a fictitious load # vs. rpm map. Full Throttle Map Utilized for worse case scenario, ok for NA, but for turbo engines makes lower than the highest boost setting non-ideal.	Idle Map Part Throttle Map Makes mapping difficult with transition from part to full throttle especially dealing with a fictitious load # vs. rpm map. Full Throttle Map Utilized for worse case scenario, ok for NA, but for turbo engines makes lower than the highest boost setting non-ideal.	Single large table of throttle position vs. rpm with compensation of barometric or boost pressure trim.

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