How much does 1 jet size affect A/F?

805moparkid said
UHH WHAT? winter air depending on the location can be dry, and if the temp isn't to low its good dense air. In the summer the air is thin, less dense, with humidity making it worse due to water content.

That is what I am saying, maybe just not saying it in the right way. We are talking about the equivalence of octane, or maybe I should say, the octane that is needed. Humidity displaces the the other air molecules and thus lowers the oxygen content, and heat makes it less dense. The two factors allow you to get by with lower octane in warm humid weather, and get away with it; with less oxygen, the mixture is 'less lean', hence lower octane is needed, and the water moderates the combustion temps, which again lowers the octane needed. Go to cool and dry, and the octane needs to go up; research in the 80's found this change to be up to 3-4 points (it's engine dependent too). I know of one turbo tuner who didn't leave a margin in for changes like this; it ran great in summer and then kablooie in the fall. I don't know of any EFI system that has a humidity sensor.....???

So if you tune A/F to the high edge in summer, you may not have any knock margin for dry, cool conditions. That is why (IMO) production cars tend to run rich for power....it takes care of all the variables inside and outside of the engine.