Originally Posted by RobertISaar
i'm..... curious, what kind of advance are you having to run with AFRs that thin? even with excellent mixing/air-fuel charge control, seems like flame speed would be super slow running twice as much air as stoich?
Very good question.
I'm running around 30* ignition advance at 30:1 A/F.
It's a major balancing act trying to keep the A/F ratio lean enough to help with pumping losses, and not slow down the flame speed to where the power drops off and kills efficiency. This is where I found out after a couple try's that I need to introduce flow to the top of the heads intake runner to create a tumble air flow effect. This help a ton with flame speed. I was running around 38* advance before I made this adjustment.
The other thing I found out is the extra back pressure from the turbo help the blow-down and improved efficiency. As flame speed slow down from lean burn the extra exhaust pressure pulled more power out of the later part of the piston power stroke.