[Formulajones]

Originally Posted by Formulabruce

The "Rich" side of things" That is key. Fuel economy, due to less dense fuel suffers at around 30% ( any new car window sticker tells the story)
You need MORE fuel when alcohol is involved, to do the Same Work.
This " can" lead to a hotter engine if not rich enough mixtures.

Yes. I think what has happened is as more people use AFR gauges and are so fixated on 14.7:1 stoich, they miss the bigger picture. For starters 10% ethanol is no longer 14.7:1, it's 14.

Most hot rods I tune don't really run all that well at those AFR numbers anyway, whether it be due to camshaft overlap, other internal engine variables, or just the simple advent of alcohol enriched fuels.

It's a better idea to tune for best drivability, and then see what those AFR's yield. Most will likely be surprised at just how rich things are running. Typically my stuff idles around mid 13's for AFR and cruises at those AFR's too. Sometimes they'll dip into the 12's for AFR when things like PV circuits open under a light throttle loads. Perfectly normal and my plugs stay clean, no issues. In fact they still return very good fuel mileage and drivability will very closely mimic an EFI car. They are just all around happier at slightly richer air fuel ratios.

Truth be told, trying to lean these things out to the 9th degree won't yield a big gain in fuel mileage anyway. In fact it's a very minimal difference.

Trying to run E85 is a different story, with AFR's typically in the 9's for stoich, yeah that's going to be a significant difference in fuel mileage.