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AFR calculation for fuel

Understanding AFR

Discussion and questions related to the course Understand AFR

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Hi all

Is there any way that I can calculate how much fuel I need for reaching my target afr ?


You can calculate how much % of fuel to add or remove by dividing your ACTUAL AFR with your TARGET AFR.

eg. ACTUAL AFR is 14.1 but you want 14.7

14.1 / 14.7 = 0.959

As its nearly 0.96 removing 4% fuel should see you really really close to the target.

Don't know if there is a webinar but in the Practical Standalone course Andre explains how to estimate fueling as he creates a map to get close before fine tuning a site. To do this you need have a site tuned first, then tune the next site and follow the trend you seen to help speed up the tuning of the remainder sites.

If you want to calculate the actual fuel mass required for a specific air fuel ratio then you will also need an accurate measurement of the air mass entering the engine. The air fuel ratio is simply a ratio between air mass and fuel mass. So for example if you were targeting an air fuel ratio of 13.0:1 and you had 1 gram of air in the cylinder then you'd need to supply 0.077 grams of fuel. (1 / 13).

This isn't a very relevant way of tuning for us in the aftermarket though. We don't usually talk in fuel mass flow but rather injector pulse widths or injector volume flow (cc/min for example).