I recently got a 2012 Ford Fiesta (2 year lease) and it has a 1.6L 4cyl engine with a quite high compression ratio, 11:1. A few months ago I got a repair manual for my old car that I'm selling, 97 Chrysler Sebring Convertible. It has a 2.5L V6 with a compression ratio of 9.4:1. There is a side note in the manual that CR a little above 9:1 usually requires premium gas to operate correctly, the Sebring gets away with 87 octane due to timing adjustment and other stuff.
In the owner's manual for my new Fiesta there are 2 sections about gas, 1 says 87 octane is the
minimum, while the other says it's the recommmended gas. Since it has such a high CR, I was wondering if there would be any benefit to using higher octane gas. I know higher octane would have anywhere from absolutely none to no benefit in my Sebring, but considering the Fiesta has such a high CR, maybe the timing and other stuff would be adjusted by the car's computer to use the higher octane.
I calculated the benefit and with gas at about $4.34/gal the 91 octane would have be about 5% more efficient that 87, with a 20 cent difference in price and originally getting either 30 or 33mpg.
Unfortunately my Ultraguage was stolen
so I can't use it to see the actual timing advance with the different octanes, will just have to use avg mpg.
I'm just curious that if one works should the reverse:
hi CR - hi octane needed - low octane used = less power/efficiency
hi CR - low octane needed - hi octane used = ?
The dealer gave me a full tank of gas when I got my car and got 30 mpg on that. I'm going to use 2 tanks of Shell 87 octane (almost done with the 1st) then try 1 on 91, see if there is a noticeable difference with similar driving styles.