I intend to run 87 octane and see if there is any noticeable difference. Been running premium and have a full tank now! Darn it! Wish I felt like running some of it out, but the allergies are keeping me inside today and it is beautiful out! Drats!:banghead
It may sound funny or hard to believe, but you can and do get better gas milage with 92 octane. I don't like to use the 87 octane because it burns up so fast. I use mid-grade 89 octane. Always had good luck with it and it is not as expensive as 92 octane.
my reasoning to use premium was not to save on mpg. Just to have the car run better. Are you telling me that the car would perform the same with regular vs 93 octane? Hard to believe but I'm just an enthusiast.
From everything I've read and heard from people who are supposed to know, if you are using a higher octane than your engine requires you are just wasting money. Higher octane will not get better gas mileage or make the engine run better or perform better.
higher octane fuel burns slower, so about the only time running premium would be helpful is if you raised the compression ratio, or the engine is pinging (from heavy carbon buildup, etc.) Because it burns slower, it may actually lower performance slightly.
Even mild pinging shouldn't be a problem because the ECM senses "knocking" and retards the ignition timing - to compensate for "bad gas", altitude, heat, etc.
It does burn a little cooler - I think the rule of thumb is about 1 degree per octane point, but in a "mild" engine, ~6 degrees isn't going to make a much difference.
I've been using any brand regular. But that changed. As I was driving to the station for my weekly fillup, I noticed a number of misfires. Just crusing down the road about 35mph, yet there was definitly a series of misfires. That time I put in Premium, since then it's been midgrade. Haven't noticed any more missfires.
Running an engine with 11:1 compression, at altitude above about 4500 feet, I can get by with 89 octane. (less air for the compustion process) As I start to drop in elevation, I must increase the octane as the amount of oxygen increases. At or near seal level, it becomes a chore to keep the car running smoothly. Of course this is a non-computer controlled car, and the SSR programaticly compensates for variations in O2.
My point is, aside from a few minor implications, (burn rates, etc, which are a function of many variables other than octane rating) the higher octane simply prevents pre-detonation. If a vehicle will not pre-detonate with 87 octane, (other factors aside) the higher octane fuels do not serve a purpose, and are indeed a waste of money.
This is a subject that could be argued for days with many variables. I usually run 89 just to be a step above the 87 and to compesate for any possibility that the 87 might not quite be 87.
Mid-Grade (89) for me in all my 87 octane trucks (I don't have any "cars"! ).
Depending upon wholesaler / refiner / geographic source / additive package, etc. all 87 octane fuel is not created equal. Nor is all 89 octane fuel created equal.
As mentioned earlier, the ECM will compensate for detected detonation by the Knock Sensor by retarding timing and in some systems (not GM) delaying injector pulse. This will result in a corresponding reduction in performance (admittedly very slight) until conditions (LOTS of variables - engine temp, ambiant temp, humidity, altitude, etc.) allow for an advance in timing to more favorable perameters.
This summer, I pulled my trailer through Idaho, Wyoming and Montana areas and I was surprised that fuel was consistantly sold in 85 (regular) 87 (mid-grade) and 89 or 90 (premium) grades. I had to by "premium" many times to get my 89 octane!
I ran unleaded plus for the first 3,000 miles then when the price of gas went up I thought I would try regular unleaded. So far there is no noticable difference in performance so I will stick with the regular unleaded until gas prices go back down to a reasonable level. As far as what grade gets the most mpg I have no idea except that my Z06 Corvette on 93 octane gets a lot better mileage than the SSR.