When does this area switch over to winter gas? And I'm assuming cars at stage 1 will need to modify the maps?

 

You can't modify a map if the gas is inconsistent, it's just the way it is.

 

I think chevron is already pumping the winter blend. My mileage took a dump this most recent tank... Car drives fine though (haven't hammered on it though)

 

switching has started over the last few weeks

"California usually converts to the gas on Oct. 31"

 

Chevon indeed has been pumping out the winter blend.. Close to 2 weeks now. My mileage dropped a bit.. but the performance is still there.

 

What is the difference in the two ?

 

Lower RVP in the summer (burns cleaner and produces less smog and releases less toxic air pollutants) and higher RVP in winter. Winter gas is also cheaper for the refinery to make so it should be a little cheaper at the pump...

Actually Chevron hasn't been pumping out winter blend just yet at least in the Bay Area, Sacramento, San Joaquin areas unless the stations are getting their fuel from 3rd party loading facilities like Kinder Morgan who usually switch formulations sooner.