A majority of cars rolling off the factory are set to run at a "stochiometric" air-fuel balance of 14.7:1. This is not necessarily the best setting but the manufacturer's setting. What most consumers are unaware of is that cars can run quite well on leaner mixtures of 50:1 or even 100:1 with additional cost-effective (cheap) supplementary and safe fuel additives. Catalytic Converter Stolen