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Old 04-28-2014, 11:47 PM   #9 (permalink)
In Lean Burn Mode
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Originally Posted by RobertISaar View Post
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.
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