Tuning with Summer vs Winter blend pump gas

[aleccolin]

I know there's a difference between summer and winter fuel blends in the US, and that it's driven by Federal regulations and is also highly regional in nature, but does anybody have any practical experience tuning in different parts of the year with these different blends?

From what I've read the main difference centers around the Reid Vapor Pressure (RVP) or basically how volatile or how easily the fuel evaporates. The EPA regulations are geared toward lowering the RVP in the summer months to improve air quality, but very low RVP is not desirable in the winter because it'll cause hard starting in the low temps so they relax the RVP limits somewhat in the winter. Summer blends are more expensive due to the additive costs, but also 1-2% more energy dense than winter blends, which is the primary reason your winter mpg may be lower.

Ethanol throws a wrench in the works because it evaporates fast and raises the RVP and also lowers the energy density. Ethanol content varies +/- a couple percent so the E10 we have around here might be in the 8-12% range.

September 15th is the changeover point for summer to winter fuel blends, so we're already on the cheap stuff. It'll be another month or two before I can get my car tuned again with the blower on, so I'm curious what impact that might have on the tuning process relative to waiting until spring.

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[ahl395]

Winter fuel is generally worse, but not a night and day difference. Most likely you will just run a few less degrees of timing than usual. Knock sensors will adjust accordingly provided you are getting a reputable tune.

Pump gas is touchy even in the same season I've seen timing vary a few degrees tank to tank.

 

[aleccolin]

I'd consider putting a half can of Boostane or similar in the tank for good measure, I don't put many miles on this car so it wouldn't be an issue to do that regularly except maybe for straight highway road trips.

 

[Nuked]

You are probably best getting it tuned on the winter gas. This will give you worst case scenario for fuel quality. I would rather the knock sensors add timing than pull it.

 

[Ryan_s550]

I dont have tuning experience between the blends, but I blend gasoline for a living and see the seasonal differences. The RVP is the main difference. We add a lot more butane in the winter blends. The RON and MON values vary a bit throughout the year, but the R+M value is very consistent.

 

[Plimmer]

You shouldn’t need to have a summer and winter tune. The o2 sensors should adjust afr and timing should adjust based on intake air temp and knock sensor feedback.

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