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Understanding AFR: What is AFR?

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What is AFR?


00:00 Air fuel ratio or AFR is the way we as tuners most often refer to the fuel mixture the engine is running at.
00:08 As it’s name implies, AFR describes the ratio of air to fuel.
00:13 This is one of the primary indicators we are watching and adjusting when we tune an engine.
00:18 Since the airflow through the engine is a function of engine capacity, RPM, and volumetric efficiency, with the exception of aspects like continuously variable cam control, we can’t influence the airflow from the laptop key board.
00:33 We can however adjust the fuel delivery and this is how we can adjust the mixture the engine is running at.
00:40 One important aspect to understand here is that when we talk about AFR, what we are interested in is air mass, not volume.
00:49 This is because air fuel ratio describes the ratio between molecules of oxygen and molecules of fuel.
00:56 Mass can be effected by both temperature and pressure.
01:00 This is why it is critical for the ECU be able to accurately measure or calculate the mass of air entering the engine.

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