Quote:
Originally posted by Brando
I notice a bit of gas mileage difference with 87 and 91. If I run some over-the-counter octane booster I notice a little better mileage. But then again I've got a later 944 that has a knock sensor.
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A bottle of over the counter octane booster will raise the octane of the 944's 21 gallon tank from 91 to 91.2. Not enough to make a difference.
Now, most over the counter octane boosters will also include a very strong detergent package and this cleaning is what yields the improved mileage.
In terms of energy content, higher octane fuel actually has slightly less energy per unit volume (not enough to be significant though). If you are seeing differences in mileage from higher octane fuels, you need to have your engine tuned up because something is mal-adjusted somewhere.