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Discussion Starter #1
I was wondering what is the basic information that a computer needs form an engine to flow a proper amount of fuel at any giver time? Im thinking its just Air Flow and RPM's. Anything I left out? Oh, by the way, what "mechanical" info does a Carb use to meter fuel?
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Well, i think that the most basic info an EFI needs is RPM and Airflow/AirPressure ...

then they usualy mesure the outside air pressure to compensate for altitude changes
and air Temp, to compensate for that.
and water Temp .. to add more fuel until the engine is hot enugh
 

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Alpha/N operation is Throttle Position, which is the least info you can get away with for EFI, but you might as well run a carb.

The most common sensors are Manifold Absolute Pressure/Manifold Air Density, Coolant Temp, Air Intake Temp, Exhaust O2 and Throttle Position.
 

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Discussion Starter #4
Ok now I have a few more questions. Whats the difference between Speed Density and Mass Air EFI setups? What does the O2 sensor used for and is it necessary?
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Speed Density is a system whereby manifold vacuum and air temp is measured to determine total airflow into the engine.

Mass Air uses a heated wire to determine the actual amount of airflow into the engine.

Common magazine groupthink on the subject is that "SD bad, MA good" based on the fact that MA allows you to make modifications to your engine without having to recalibrate your controller - it will adjust automatically to the increased airflow to a certain point. This is fine if you're modifying a stock engine slightly. Anything more and you have to recalibrate.

Mass Air is more complex than Speed Density in terms of the sensors required, plus the restrictions on airflow it has. If you're going to be playing with the VE tables in the computer anyway, SD is the simpler way to go in terms of setup and maintenance.
 

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Oh, the O2 sensor is used to adjust the A:F ratio during engine operation, or can be used for initial tuning. It's recommended but not needed.
 
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