Hi, does anyone have and safe optimal AFR numbers for a blown engine.

Just running in an engine with a AMR300 on it, starts and runs fine, but when I bring the AFR down to the 9's she is choking herself! Seems happier around the 12's

Any information would be well received.

I seem to remember seeing something on Tomorrow's World a long time ago when Ford were developing their "Lean-Burn" technology, which burnt unleaded fuel at 14 AFR so 12 to 12.5 sounds about right. Figure appears to be borne out by surfing tuner's sites regarding forced induction set ups.

Googling it 12,8 peak TQ 13.2 peak HP on a supercharged motor on Offsure only.com
I thought lean burn ratios were around 17:1 ?

Location: Midlothian

Thanks for the replies, I'm using a wide band sensor fitted in the four branch manifold going to a dedicated digital output. I ask the question as I was advised that old sidevaves run rich when happy, I also run a 440bhp turbo race car so appreciate the importance of a knowledgeable AFR, The engine seems happy around the 12's as you have all kinda stated, I am racing the engine in 6 weeks so I don't want to run her lean and pick up a ring or piston. The afr for Turbo and Supercharger does not seem to far apart even though the technology used is planets apart on my applications.