Now, on top of this, O2s will be different in a Texas summer versus a Canadian winter. Because of the much colder winter air, I can get away with running a much leaner (lower O2 readings) in the winter than the summer. Taking my car as an example (Supercharged (or turbocharged) cars with an aftermarket cam) I say that 920-935 O2s are good. In the winter, on the same car, I could easily go down to approximately 915-925 without any increase in KR. If you live in a hotter climate, you may need to add 10% to the O2 numbers that I suggest. These are approximate O2 numbers and nothing is set in concrete... your car, tune and KR numbers will ultimately dictate what A/F ratio your car runs best at.
