I run 87 in my 3.5, just returned from Florida and I had 18mpg highway. This was 70mph w/aircon on 32's. During my 1hr mixed commute I get 16mpg.

My high mpg was around 21mpg with the factory 265/70-15's

Is there a difference with the SOHC engines VS the DOHC? I know mine is the DOHC and 92 octane is recommended.

Compression maybe? The dohc was in the range of 9.5:1, maybe as high as 10.5:1. Some one kick me for not remembering the exact number. <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/shiner.gif" alt="" />

The last tankful that I checked the mileage on was 15.2 mpg. That's my wife driving back & forth to work and miscellaneous trips around town. That's running mid-grade (89 octane) and no a/c usage.

Higher octane does have to do with MPG. Reason being is it does not burn as fast as a lower rated octane gasoline. There are plenty of people who use premium in there low octane vehicles to obtain not only better gas mileage but a better quality fuel. I also have seen the difference in my dd saturn. And i actually hammered on it to see if it was the placebo effect. Numbers speak for them self. just my
.02 <img src="/forums/images/graemlins/cheers.gif" alt="" />

Where are these "numbers" you speak off. I've never heard of high octane giving better MPG. Premium is not better quality fuel.

"The fact is that the overwhelming majority of cars on the road today do not need a high octane gasoline to run properly and efficiently. Octane ratings are a measure of a gasoline's ability to resist engine knock. "Knocking" or "pinging" in an engine results from an uneven burning of the fuel-air mixture. If your car is not "knocking," using a higher octane fuel will do absolutely nothing for you but waste your money. The fact is that regular unleaded gasoline, 87 octane, is the recommended fuel for most vehicles. You can determine what fuel is recommended for your vehicle by checking your owner's manual.

If you are using gasoline with an octane rating greater than 87 and your engine is not "knocking," drop down to a lower octane gasoline. If your engine begins to "knock," go back up to the next octane level. Remember, octane is nothing more than a measure of anti-knock quality...use the lowest octane fuel which provides you with knock-free operation.

Another myth is that use of a high octane fuel will improve fuel economy. The fact is that fuel economy is determined by a number of variables, including the energy content of the fuel and the condition of your vehicle, neither one of which have anything to do with the octane level of the fuel. In fact, two fuels of identical octane could have different energy content due to a difference in composition.

One last myth is that the name of the grade of fuel is an indicator of the quality or octane level of that fuel. These names should not be relied upon when you are choosing which fuel to use. The fact is that you should always choose your gasoline by checking the octane rating on the yellow sticker on the gas pump. By so doing, you will be assured that you are buying the gasoline that you want and, by using the lowest octane that still provides you with knock-free operation, you can save a significant amount of money on your gasoline purchases."

http://www.co.suffolk.ny.us/webtemp3.cfm?dept=3&id=2049

Well, I have a little different opinion.

1. In general higher octane will not affect the efficiency of your engine or give you better mileage, but...
2. If you have a newer car that calls for high octane gasoline, and you put in low octane instead, the following will happen. The computer will detect knocking with its knock sensor and retard the timing. Retarding the timing will reduce your max availible hp/torque and will reduce the efficiency of your engine. Thus, your mpg may go down if you use lower octane gas.
3. Some econobox cars have engines with knock sensors. While most economy cars specify that only low octane gas is necessary, the cars computer may adjust if you put high octane in. It will advance the timing, thus giving you more hp/torque and efficiency under some circumstances. I believe the GM ECOTEC engine used in Saturns and Cobalts, etc has a knock sensor in all versions.

Typical blog huh? Everyone has a different opinion.

02

I also disagree. My dd is a 93 Nissan 240sx, which I autocross in the SCCA occasionally. The engine is completely stock except for Iridium plugs & Magnecor wires. The factory recommendation is for regular unleaded gas, but "premium unleaded is recommended for maximum performance". I've used a friends G-tech to do some experimentation with different octane fuels, and found that with typical 87 octane fuel the car will do 0-60 in 7.4 seconds. When I filled with 91 octane premium, that time was reduced to 7.2 seconds. When I used 101 octane race gas, the 0-60 time was 7.1 seconds. These times are averages of multiple runs, all done with approximately 1/4 tank of gas. The engine management system is apparently capable of adjusting the ignition timing to compensate for the added or reduced octane of the fuel, but only to a certain point. I thought that I'd get more of an improvement with the race gas than I actually did.
Anyway, the point is that added octane can make a performance difference in some engines.

this is the exact mileage I get on 87 also. I know everywhere in the manual and the gas lid it says to run high octane. i have run 87 for the past 4 years with no knocking unless I get cheap gas. Will it get better with high octane? I don't know cant afford it.

i get 4.5k/liter on my 3.5gdi swb, all ciy driving... using 97ron fuel. bad ratio =(