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EFI Tuning Fundamentals

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Brake Specific Fuel Consumption....

It has to be measure at some specific RPM? Or in the peak of the HP?


BSFC can be measured anywhere you like. The figure will vary depending on what you are aiming for, do you want to know what the efficiency is like at peak power or peak torque, or elsewhere?

As an example, Honda map it as a function of RPM on this power graph on page 5 of this document, so they can see where the best efficiency lies while still at full throttle --> http://www.k20a.org/upload/HondaRA168EEngine.pdf

There are also graphs that show BSFC as a function of intake temperature, boost pressure, equivalence ratio, fuel chemistry, fuel temp.

It's not a one size fits all measurement, and if it's presented as a single value by itself, you really need to ask the question which point on the map was it measured at?



To measure brake specific fuel, you need to know the fuel mass flow and the brake horsepower. That means you either need an engine sitting in a lab somewhere to measure it directly or you need to back calculate those two factors from other information.

BSFC = (fuel mass flow [grams/sec] / power [kW]) * 3600

If you know the airflow through the engine (mass airflow sensor if the car has one) and the air fuel ratio from a wideband o2 sensor you can calculate the fuel flow. If you know the power at the wheels from a chassis dyno you can assume some amount of drivetrain loss and calculate the brake power from that. Or you can calculate the power from the engine's ECU torque model if it has one and you have access to that parameter.

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