Originally Posted by Euromedic

So I made a few adjustments based on discussions here, after purchasing the Fit new. Tire pressure to 45 psi, fuel usedswitched from 87 to 89 octace, matching shifts and revs. 5300 miles later, my average calculated MPG jumped from 34 to 37. Sure is nice to see the avg MPG counter increase instead of decrease, as was the case in my previous car (23 mpg average). Btw, based on 60/40 percent highway/city driving.

Have a few more ideas to complete, goal is to break 40 mpg mark on constinent basis.

Originally Posted by SilverBullet

Also if your mpg drops from the heat you will have to step up the octane too.

Originally Posted by Steve244

Let the wild rumpus begin.

Paying for higher octane in an economy Honda is not why we bought the cars. Even when it heats up. Other than anecdotes and feelings posted here there is no literature to suggest any car that doesn't require higher octane actually benefits from it in terms of increased MPG. There are an equal number of anecdotes claiming no difference, even from those that initially drank the kool-aid.

There is a valid argument that it might increase top end power a tad, but this has not been documented, and wouldn't be part of any argument to save fuel.

When my Fit was new, I averaged 32 mpg. It increased over the first 15K miles to 34mpg. At 30K I changed the tires to Michelin Energy, had it aligned, and switched to 0w20 synthetic (current models come from the factory with this). At this point it increased to 36mpg (6.53L/100KM). My drive patterns have remained unchanged over this period.

This is over a 50 mile per day commute 75% freeway stop-and-go and 25% suburban street driving in Metro Atlanta. 87octane with lots of ethanol.

Originally Posted by Road and Track

The simplest answer of which fuel to use is to follow automaker advice contained in your car’s owners manual. This might be given as a requirement or merely as a recommendation. The latter might be qualified by a statement along the lines of “lower octane may yield reduced performance or inferior mpg.”

The reason for this has nothing to do with energy content. In fact, depending on its blending, a premium fuel may actually contain less energy per unit volume than regular. However, its potential for producing more power and enhanced mpg goes back to MBT and that knock sensor. If premium is recommended, this is the engine’s optimal fuel. It’ll run on regular—albeit with the sensor invoking ignition timing that’s less than that associated with MBT. And with less than Best Torque, there’ll be less performance and an mpg hit.

If the engine is tuned for regular but fueled with something of higher octane, things are a tad more complex. Most modern knock-sensed ignitions seek MBT timing and thus, at least in theory, profit from the added octane. Some, though, have preset ceilings beyond which they won’t advance.

And, in all cases, the differences depend on engine families, their octane sensitivities and intended performance levels. Without a stopwatch or dyno—and apart from your pocketbook—you may not even notice any detriment or benefit.