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Boost formula

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Hello everyone,

Is there a way to calculate the AFR needed as boost increases for example, if u need 11 AFR for 1 bar boost how much will i need for 1.5, 1.8 etc..

You pretty much never need 11afr... Except possibly endurance racing a Subaru ej257 on pump gas:)

Considering what you asked and how - you really should watch the courses and webinars. I found that it's explained rather well.

Have a look through the webinar archives as find the effects of AFR on engine torque and also the effects of AFR or EGT, both will explain what adding too much fuel can do to your engine.

There's also this on on planning your AFR for forced induction:


The air fuel ratio doesn't continue to move richer indefinitely as we increase the boost. There is a practical limit beyond which you're likely to struggle to achieve consistent combustion. Very seldom will I end up tuning a turbocharged piston engine richer than approximately 11.5:1. You'll also typically see the power begin to drop off as you move richer than this.

As Toxin has mentioned, in some unique situations such as land speed racing you may need to focus on thermal management in favour of outright power and tune richer to keep the engine alive, but this would be a fairly unlikely scenario for most tuners.

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