look at the graph at the bottom,
notice the power output changes less than one percent
from .075 to .087 fuel to air.

Is there any benefit in going richer than
.075, 13.3 to 1, ,, other than a minor reduction in temps?

perhaps, there might be a benefit if the spark-timing
is limited by knock, if you know, please discuss,
but keep in mind that I don't subscibe to concept
that every car problem is fixed by going richer.

This graph is aircraft related,
and yes, I know that a plane is not a car.

 

No, not usually....

Every engine has a slightly different A/F ratio that results in the peak of that power curve. For a typical SBC on modern pump gas though, it's almost always somewhere in the range of 12.7 - 13.1. Going very far outside of that range is rarely if ever going to produce desirable results.

If the engine spark-knocks, and you can fix it with fuel, then you can probably also fix it with timing. Fuel is just a band-aid. Again, most typical N/A SBCs, will run their best with the "total" timing (not including vacuum advance) in the 34-37° area. And again, if you have to go very far from that, then something is wrong with the way the motor is built.

If the motor spark-knocks with best-power fuel and timing curves, then it's built out of a wrong combination of parts for the application. Sure you can maybe cover it up a bit by wacking one or both of those curves; but the real "right" answer is to fix whatever is causing the setup to be wrong in the first place.

 

Actually, that graph is surprisingly close to what I have experienced on tuning EFI cars on a dyno. I find max power somewhere between 12.8-13.0 with 13.0 being my target.

I also find that while running richer than 12.8 doesn't seem to have as much of an adverse effect as running leaner than 13.0; you really seem to notice a power loss when you hit richer than 12:1.

The only problem I do find on the "new cars", many can't tolerate too much spark at all without detonating. Small CC heads really seem to be prone to this. I find many of the stock L98 heads cannot handle more than 28* of spark without detonating. Some can't even handle 25*.