Doesn't it depend on the vehicle? If you have an older model that isn't computer controled then the timing can't be adjusted per the octane used and so your just wasting money. Right?
I was also under the impression that higher octane burns slower, so in a low compression engine that means carbon build up due to low flame speed, which in turn leads to less energy and lower mpg.
Don't ask me why but my father-in-law and I did a little test. On our trip to Fl. a 9 hour drive we filled up his 98 Eldorado with the NorthStar engine, which requires premium, with regular gas. When we stopped for gas after one tankfull ran through the engine we averaged 27 mpg, filled up with premium, same brand of gas, ran that tank the second leg of the trip, same speed, same driving style the works, when we filled up we lost 2mpg. Didn't make sense and to this day he will not run premium in it. I know it is not a good thing but try to tell that to a 79 year old who is set in his ways.
I run what ever my manual calls for. Don't see the need to spend the extra cash on something that I don't see a benefit using in a stock non highperformance vehicle. Now in my 65 Impala that has close to 11:1 compression then the higher octane works well and it runs better. Plus I think that back in the day with leaded gas the octane was a little higher then anyway, correct?
Now like in his vehicle you would think that running premium the mpg would go up because the computer can advance the timming as far as possible and with highway driving the higher advanced timing the better economy, at least that is my understanding. Just don't see why we got less mileage.
