Winter vs. Summer Blend - HP Loss Question

[vettenuts]

I had an interesting thing happen today and wanted to get some feedback. I have had my car on the dyno several times and the results are pretty consistent. Today, the curve was down throughout the RPM range with peak power down approximately 10 hp or 2.7%. While trying to sort out if there was a mechanical issue, one difference between my last dyno and today was I am now running a winter blend of fuel (having filled a couple of days ago). Is there anyone that has technical information on the differences in blends that could account for this? My understanding in limited reading thus far is that winter blend has more butane, which in turn has a lower energy content resulting in a lower energy content in general as compared to the summer blend.

 

[umungus1122]

Winter gas does have more butane than summer blends. The higher butane blends are cheaper to produce and also increase the vapor pressure of the blend for easier starting in very cold weather. Summer blends have more of the longer hydrocarbon chain components that have more BTUs. Try the website called the Oil Drum for more reading.

 

[vettenuts]

Thanks. The interesting things is the two curves are pretty much parallel so the change affected the entire RPM range. The fuel seems to make sense as possibly being the cause.

 

[lexus114]

Just more [censored] shoved down our throats!! (that we cant seem to do any thing about)

 

[Bamaro]

Originally Posted By: lexus114
Just more [censored] shoved down our throats!! (that we cant seem to do any thing about)

I think winter blends have more to do with better cold weather performance and summer blends are to cut back on pollution.

 

[mechtech2]

Winter blend fuel is an improvment in cold weather.
It vaporizes easier. This was more important with carburetors, but still is valid for fuel injection.
Running oddities can occur in the intermediate temps - fall and spring, when switchover occurs.
But less power on a dyno because of it? I don't think so.