1968 Shelby GT500

Engine Load

Before you can start planning a fuel injection system you need to know your engines needs, and what kind of driving you’ll be doing. The big engine notes to be made are displacement and cam profile. You should always match displacement in the program, and cam profile always effects inlet airflow properties.

Load is the a measurement of how hard an engine is working which is measured in percent. Coasting down hill is considered very low engine load. Pulling a weighted trailer uphill is considered high engine load. Engine load is usually measured by taking a reading off the inlet air flow The main factor that chooses which EFI system to use is AIR FLOW. Air flow is the biggest unknown factor when calculating fuel ratios and timing curves. Air flow is so unpredictable that people get grant money to study wind tunnels. So to decide which fuel management system to use depends on how unpredictable the air flow into your engine is.

As you read over the table below you’ll notice that Speed Density is not an underachiever and Mass Air is not the superhero most people want. It’s all in the programming. You can not take a stock automobile computer, build a super engine for it, and expect it to be a drag strip killer. Programming rules the land of fuel injection. Speed Density can be programmed to handle more power than Mass Air. Mass Air can be programmed to be more exact that Speed Density. This exactness is what makes Mass Air more desirable.

There are four styles of fuel injection programming that I know of; here is a side by side comparison of them:

 

Mass-Air-Flow Speed-Density Vain-Air-Flow Alpha-N

Dominant
Sensor

MAF
Sensor
MAP
Sensor
VAF Sensor TPS Sensor

Reference
Sensors

  • Temperature

  • Temperature
  • RPM

  • Temperature
  • Barometric Pressure

  • RPM

Primary
Uses

  • Mild performance engines
  • Engines with mild inlet airflow
    characteristics
  • Engines With high emmisions and economy
    demands

  • Low power docile engines
  • High performance engines with harsh
    inlet airflow
    characteristics
  • Engines that need boost sensing
    incorporated
    into program
    calculations

  • Low power docile engines
  • Museum exhibits?

  • Race engines with poor vacuum
    characteristics
  • Race engines where inlet airflow is
    unpredictable
  • Engines that other EFI systems can’t
    handle

How
it works

  • Air mass vs engine
    temp in main table.
  • Knowing the Mass Air entering engine
    makes calculations more
    exact.

  • Manifold vacuum vs engine temp in main
    table.
  • Can be somewhat stable if oxygen sensors
    are perfect

  • CFM vs engine RPM in table with many
    additional functions still
    not very accurate
    compared to today’s
    technology
  • using CFM for calculations is more like
    guessing than math

  • Throttle position vs engine RPM in
    table with no additional
    input allowing massive
    amounts of boost and nitrous
    to be considered
    by the user

Highlights

  • Can compensate for altercations to engineand properly meter fuel
  • Can compensate for aging engines with
    diminished performance
  • Does not rely upon other sensors to
    make general fuel ratio
    calculations

  • No inlet sensor restriction
  • Calculations required by boosted
    applications
    can be made

  • Part of EFI history?

  • Quickest reaction to throttle change
  • Works on race engines with hostile
    airflow
    characteristics

Down
Faults

  • MAF sensor can impede maximum inlet
    airflow
  • Pulsating inlet airflow characteristics
    trick MAF sensor
  • Program calculations required by boosted
    applications will not be
    sensed
  • Does not react to throttle change as
    quickly as SD or AN

  • Can not compensate for changes to
    engine
  • Aged engine loosing efficiency
    over time is not sensed nor
    compensated
    for in calibration
  • Oxygen sensors can fix fuel rations
    in closed loop, but not
    ideal to rely upon
    them
  • Does not react to throttle change as
    quickly as AN

  • Sensor is a large restriction to inlet
    airflow
  • No tolerance for unstable inlet
    airflow
  • Technology using CFM sensor is
    outdated
  • Oxygen sensors can fix fuel rations
    in closed loop, but not
    ideal to rely upon
    them

  • User must take complete responsibility
    for all program
    calculations
  • Fuel management control very
    inaccurate
  • NO environmental changes used in program
    calculations

There are 2 different modes fuel management systems can operation in:

Open-Loop

Open loop defines the engine operation when the fuel ratio is calculated with consideration to only input signals from the main sensors in the program style (MAF / SD / VAF / AN)
Programmable fuel management systems can be operated in 100% open loop very effectively.

Closed-Loop

Closed loop defines the engine operation when the fuel ratio is calculated with consideration taken from the main sensors and feed back sensors like the exhaust oxygen sensor (HEGO). Closed loop operation is devoted to emissions, economy, and a Stoichmetric fuel ratio of 14.7:1
Programmable fuel management systems can not dominantly rely upon closed loop operation without severe engine damage, performance loss, or other problems

There are 2 different modes of opening fuel injectors that are used by fuel injection computer programs:

Bank Firing Injectors
Bank fire means that the injectors are divided into 2 groups. On V8 engines cylinders 1 4 5 and 8 open together and cylinders 2 3 6 and 7 open together. This creates an equal distribution of fuel atomization inside the intake manifold.
This usually works just fine on engines, in fact you can buy an after market programmable fuel injection management systems that is bank fire and can support 1000+ horsepower engines.
Bank Fire program is not dependant to the firing order of the engine. The injectors do not match the spark order of an the engine equal distribution of fuel atomization inside the intake manifold still exists Idle quality and fuel economy can not be as greatly tuned as Sequential can.

Sequential Firing Injectors
Sequential fire means one injector is fire a while the intake valve is open. This creates an equal distribution of fuel atomization inside the one intake manifold runner during the intake stroke of that cylinder..
The programmed time of when to open a injector is matched to the camshaft grind profile. People get into trouble here because camshaft swaps that do not match the program can affect low RPM stability of the engine.
Sequential Fire program is also matched to the firing order of the engine. If the injector order does not match the spark order of an engine low RPM stability of the engine will be lost. High RPM will still create an equal distribution of fuel atomization inside the intake manifold. But idle will suffer poorly.
Sequential Fire program gives greater ability to program better idle quality and fuel economy, but it must be all matched in the program for these gains. There is NO performance gains to be had from sequential firing injectors.

This page does not reflect Ford programming or computers in general, but applies to ALL EFI systems

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