Octane level

Messages
36
Location
Brewster, NY
I own a 2001 Audi TT 180 Quattro and the owners manual says the car requires 91 octane or higher. Since gas prices are getting very high I was wondering if I will damage my engine in any way by using 89 or even 87? Since I use this car to commute on the highway 50 miles each way I'm ok with a slight loss of power if I will save money at the pump. The car in 100% stock. Any thoughts will be appreciated! Thanks!
 
Messages
699
Location
Texas
Your mileage/gallon will probably drop by running a lower octane since the ECU will adjust. You may want to experiment, but I've found it is just a wash.
 
Messages
783
Location
Austin Texas
Every new car sold in this country has to be able to run on 89 (or is it 87) octane and not self destruct. The ECU will pull timing and may richen up the mixture to compensate. But afte 50 miles or so, the ECU will 'learn' this new gasoline and run happily if not so peppy.
 
Messages
74
Location
MD
I know of a few cars where people have reported pinging with 87 octane where 91 was recommended. If you want to give it a shot, you might want to start out with only a few gallons of 87 or 89 just to make sure you don't have any problems. If the car starts pinging, you can always add some octane booster and fill the tank the rest of the way with 91.
 
Read that owners manual carefully. If it says "recommended for best performance" or something alonf that line, then you can safely step down to 89. If you are running high compression 13:1 or higher and that manual says MINIMUM 91, then follow it !!
 
Messages
3,094
Location
Metro Detroit
^^^^^What he said. You have to read between the lines in your manual. Some cars can get away with lower octane than recommended, some can't. Go by the book.
 
Messages
3,558
Location
SE Pa
Miles per gallon and the minimum design octane are only parts of the equation. Depending on the ECU and engine design, switching to 87 in a premium fuel engine at today's pump prices may not yield the best miles-per-dollar value. In most markets, the price spread between regular and premium grades remains just 20 cents. When regular was $1, that was a large price difference. But at $2.50, it's under 10%. As the price of regular moves closer to $3 this summer, the price difference will dip below 7%. Your ECU is going to compensate for the lower octane by retarding timing. Fuel efficiency will drop. If the mileage drop is more than 7-10%, then you should stick with premium fuel. You'll get more miles per dollar spent. So monitor the MPG drop very carefully if you're switching to save money. Of course, this doesn't even factor in the loss of fun factor with some engines that are optimized for premium fuel.
 
Messages
1,420
Location
Balto.
Your engine should adjust to a lower octane rating but I think the only effect should be a slight drop in performance but your mpg shouldn't be negatively effected. And unless you normally use WOT, a little performance will not really be noticed that much.
 
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