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Practical Standalone Tuning: Choosing Air Fuel Ratio

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Choosing Air Fuel Ratio


00:00 The correct air/fuel ratio is a source of constant debate, and there's no firm rule about what air/fuel ratio you should run for a particular combination of RPM and load.
00:10 The correct air/fuel ratio will depend on the engine, the fuel, how much power you're making, and how the engine will be used.
00:18 This course isn't designed to give you the exact numbers to put in your map, but rather how to adjust the fuel maps to achieve your target.
00:25 It's still worth understanding how air/fuel ratio will influence the engine though so you can have a better idea of what you should aim for.
00:34 Most people understand that we need enough fuel to match the amount of air entering the engine.
00:39 As we increase the engine load, we need to add more fuel to ensure that we are properly utilizing all of the available oxygen, but also the additional fuel is used to help control combustion temperature.
00:51 Basically, the more power an engine makes the more fuel we need to add to control combustion temperature and prevent engine damage.
00:59 For a more thorough explanation of these terms and how they affect engine performance, refer back to our EFI Fundamentals course.
01:08 For our example, we're going to aim for a target lambda of 1.0 in the idle and cruise areas of the map.
01:15 At wide-open throttle, we're going to target a lambda value of 0.90.
01:20 As load increases, we're going to smoothly blend between these two targets.
01:26 I'm also going to aim a little richer at high RPM to help reduce exhaust temperature and protect the catalytic convertor.
01:33 From 5,000 RPM, we're going to smoothly reduce the lambda target from .90 to 0.87.
01:40 At the same time, I'm going to target a richer mixture of 0.95 in the low-load areas at these RPMs.
01:48 We're only going to see this area of the map when the car is being driven hard, and again the extra fuel will help control combustion temperature.
01:57 If your engine is turbocharged or supercharged, you'll need to run the engine much richer in boost.
02:03 Most boosted engines will want to see a lambda of 0.78 to 0.80 at high boost to ensure engine safety.