What air/fuel ratio can do damage

[Arthur]

Related to 1999 mustang cobra with blower.

I cannot find any information on what air/fuel ratio can do damage to your engine.
I read somewhere that if you have too rich a/f ratio then you can wash oil off the cylinders and permanently damage the engine.
If you have too lean condition then you can melt the piston.

But the main question what exactly numbers range are they?

I found this table that explaining but not telling the dead end for you engine:

• 6 AFR - Rich Burn Limit (engine fully warm)
• 9 AFR - Black Smoke | Low Power
• 11.5 AFR - Best Rich Torque at Wide Open Throttle (WOT)
• 12.2 AFR - Safe Best Power at Wide Open Throttle (WOT)
• 13.3 AFR - Lean Best Torque
• 14.6 AFR - Stoichimometirc Air/Fuel Ratio Value (Stoich)
• 15.5 AFR - Lean Cruise
• 16.5 AFR - Usual Best Economy
• 18 AFR - Carbureted Lean Burn Limit
• 22+ AFR - EEC / EFI Lean Burn Limit
  
  If someone has this knowledge please share!
  Thank you

 

[smashedheadcat]

Ford set the 03-04 cobra at 12:1 (.82 stoich). I’d say the consensus is that it’s on the lean side of conservative, but fueling isn’t the only variable.

Washing the oil off of the cylinder walls: My opinion.... nothing to worry about. You’ll be hard pressed to find an engine failure on this board from that. Also note, e85 stoich is 9.85(ish):1.

After all that yapping, if you’ve got a blower on a stock block 99 cobra, keep the power in the 400rwhp range if you want it to stay together. You can get that with a fat fuel table, low timing and low boost. If you want to cook it, run pump gas, 12.2 afr and MBT timing on 15psi.

 

[biminiLX]

For your question I’d actually look at a/f as lambda so that you understand the goals and limits of the ratio no matter the fuel used.
I usually try to keep WOT lambda at 0.80 for my combo at higher boost/timing.
-J