Better to run lean or rich

[thexav]

Which is more favourable in a performance engine?

Running rich or running lean? What are the advantages and disadvantages of each?

 

[SLEEPER]

neither is good but i suppose if you must pick one i suppose rich is better or maybe less worse would be more accurate

some ecus can control the fuel mix to a pre set reatio so theroretically the run right all the time

 

[TCJBOLDIE]

From what I have learned over the years it is better to tune a boosted motor slightly on the rich side as protection against detonation.
As Sleeper has said the latest top of the range aftermarket ECU's can control the AFR'S automatically across the rev and load range to whatever the tuner sets it to in one fell stroke without having to do so in say 500 rpm steps/increments.

FWIW my tuner showed me the AFR'S which showed a neat almost straight line that he "fattened" = made richer at the top end. My ECU is a Haltec E6X which is a bit old hat but still does the job and it would set me back app $3000.00 to upgrade.

 

[T9 man]

Well if my Euro lottery winning line comes up tonight Rad, you can have that ECU upgrade with my blessing

 

[TCJBOLDIE]

Well if my Euro lottery winning line comes up tonight Rad, you can have that ECU upgrade with my blessing

Now that is what I call a "win win " result with big all round.

 

[RobBentley]

Excess fuel cools an engine as strange as it sounds and this in part also helps against detonation particularly on turbo as mentioned. You'll see most factory turbo maps set to run rich at high rpm and load as a result. Lean is by far a much quicker way to kill an engine. Not only will you risk lean detonation but you'll also raise exhaust gas temps which can cause damage to the turbo.