Originally Posted by The Forgotten On

.... The only ones that can get away with normal gas are 80-84 L-jet cars.

Originally Posted by dr bob

Less than a year into 928 ownership in the late 1990's, I was driving back to SoCal from a Devek event, hot August day. I stopped for fuel and accidentally put regular into my S4. Even with all the spark-retard and knock-sensing systems intact, it still complained with a few audible pings and continuing poor performance. I drove it gently for the rest of the ride home (maybe 50 miles), and ended up transferring most of the remaining fuel to my other less picky car's tank.

Fast-forward to today. Fuel quality here in Oregon is much better than what is available in southern California. Mileage is much better here, some because of lack of traffic I'm sure, but mostly because the fuel blend is much better. I've only passed a couple tanks of fuel into the 928 since arriving here, still enough to see 22-25 MPG average results. The Honda has done much better too, with mid- to high-twenties mileage here vs. high teens in SoCal. I have an OBD onterface set up on the Honda to datalog to my tablet. One of the available parameters is the sensor that reads the amount of ethanol in the fuel. In California it showed around 12% most of the time, but sometimes showed as high as 20%. Mileage was affected almost directly by this number. Local fuel here shows no ethanol at that sensor, and mileage has improved by some 20-25%. Again, driving patterns have changed too, so I can't attribute it all to the fuel.

On other past "regular gas " cars with knock and exhaust oxygen sensing, premium fuel would often more than pay for itself in improved fuel mileage. I'm pretty religious about tracking miles and costs, and with the increase in gas costs over $3/gal even the "just needs regular" cars would improve enough percentage-wise to justify the extra twenty cents fer gallon for premium. The cars also saw mileage and performance improvements with new oxy sensors, easily enough to justify replacement every 40-50k miles.

Originally Posted by Jetdriver69

Back in 87, I put half premium leaded and half 110 octane aviation gasoline into a gray marketed 79. I ran like a scalded cat, but avgas was and still is very expensive.

Originally Posted by SteveG

How many people don't have an Owner's Manual or haven't read it? Amazing.
Like the New Visitor thread, it has a lot of information in it very useful to the, ah, O w n e r.

Originally Posted by The Forgotten On

Winter blend gas gives you less mpg's. That is also why it is cheaper than other seasons.

Originally Posted by safulop

Here in the Central Valley I find the winter mileage is really up and down. I often find the mileage improves in winter, probably due to the ideal operating air temp and not running A/C, but then at some point the gas blend does change or something and the mileage suddenly drops by about 1 mpg at some point during the winter months. The best mileage is during late Fall when temps are ideal, A/C is not running, and most stations are still pumping "summer gas."

But then, due to my fabulous *Autothority* chips my city mileage is horrible no matter how you skin the cat.

Ordering the Porken chips any minute now. . .