I understand they'd require more fuel>>>> (archive)

but this is because they force in more air into the combustion chamber. So keeping the A/F 12.7 even with a turbo, would theoretically still be the best power output.

Maybe this may change a bit, since the air coming in from a turbo isn't as dense as outside air... just a thought.

Boris

Just making sure I have this right... optimal A/F is 14.7:1, and Max Power is @ .86 multiplier? about 12.7:1 or so?

Got another question, while at it.... if 14.7 is optimal, then why is running a bit more rich (and ONLY with the .86 multiplier be the max power output?) Any engineers out there?

It all depends what you want to optimize. Modern engine control computers target an AFR of 14.7:1 at idle and part throttle because that AFR gives the best compromise on emissions (ie, the lowest emissions). 14.7:1 is not the best for mileage or power, just emissions.

As far as max power at WOT is concerned, every engine is different with respect to how much fuel they like for max power. Typically though, it's always richer than the 14.7:1 ratio. The 12.7 AFR you indicated is a good ballbark for a naturally aspirated engine. Boosted engines typically like more fuel.

Nick
'95 M3 turbo

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