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Best AFR for light boost

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G4+ / VG30ET / GTX3067R / wide open throttle

I have set my AFR target for 1400rpm @ 1psi (14.1) to 2250rpm 5psi (12.4:1). I was recently told by a local tuner that it is common for them to tune engines 1 - 5psi boost (1000 - 3500rpm) at or very near 14.7:1 AFR to improve mileage and torque. What is your advise on this matter?

I look forward to your reply.

David

I have heard / read that leaner AFR during low boost assists in turbo spool. Any validity to this?

Under low boost conditions as the turbo is spooling up it's not necessary to run as rich as 12.4:1. I'd suggest aiming for somewhere around 13.5:1-14.0:1 at 100 kPa/0 psi and then gradually taper towards your full boost target.

A leaner mixture in the spool area will result in a higher EGT and this can in theory aid boost response. My own testing suggests any difference is marginal but even aside from spool, there is no need to be so rich at such low load and you're just burning unnecessary fuel.

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