On a supercharged car what is the propper air/fuel ratio to have? And what are the dangers of having one that is too high?

 

The chemically correct air/fuel (A/F) ratio for gasoline is approximately 14.7:1 but best power is achieved at richer A/F ratios around 12.0:1.

This is partly because of the charge cooling effect of the extra fuel and also because the presence of slight excess fuel means all the air in the charge will be burnt.

running a high AF Ratio means you're running lean, which is a fatal problem for forced induction, potentially causing knocking/detonation which in turn can damage your engine.

 

Would an A/F ratio of 11.7 or 11.8 be too high for a supercharged car?

 

nope.. that's just about right IMO.
as a matter of fact, anything a bit lower than 12.0:1 (i.e rich) is a bit on the safer side

 

if i am running just a little rich does that cause the black buildup on my tailpipes?

 

Are you reading that from a bung before the cats (or if no cats close to the headers)?

If you're reading that from the tailpipe sniffer it's going to be slightly different reading .1-.3.


To answer your question, though... running just a little bit rich isn't going to cause carbon buildup on your tailpipe. It will, but over time. Running a good bit rich will do it much quicker.

CR
Tillman Speed
610-497-3711